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Introduction

Various optical systems, including lenses, mirrors, and spherical mirrors, reflect or diverge light to create various kinds of images. Rules of reflection and laws of refraction are the two fundamental laws that govern picture generation. In the creation of images, these laws are crucial. Different-sized pictures are created at various positions when light is reflected by lenses or mirrors. It can vary in size from very little to extremely large to the same size as the thing, and it can also become blurry at times. Consequently, the creation of the hazy image is referred to as an abbreviation. A hazy image is created when light rays diverge after passing through a lens in a particular spot. This is known as an aberration of the lens. 

Lenses and curved mirrors are two objects that can induce optical aberration. This phenomenon causes a deviation in the light rays. Not all of the light’s beams concentrate on the focal point. By virtue of optical aberration, images are essentially blurry.

Types of Aberration

For a single wavelength light, there are five types of aberration.

1. Spherical aberration
2. Coma
3. Astigmatism
4. Curvature of field
5. Distortion

Let our expert guru Mr. Mayur be your guide toward improving your understanding of this chapter better. Watch the related video of this chapter in Class 7th Science lesson no-15

1. Spherical aberration

It is a defect of the lens due to which the light beam does not concentrate at a single point, as a result, the exterior part of the image gets blurred. This aberration is caused in lenses or mirrors when light beams fall on the exterior part and concentrate at different points.

Correction of the spherical aberration

• Spherical aberration can be corrected by using a mirror of different non-spherical shapes. A parabolic mirror or an ellipsoidal mirror can replace a spherical mirror.
• Spherical aberration can be removed by blocking the marginal rays. A circular annular mask on a lens can remove the marginal rays.
• By using suitable radii of curvature of the two surfaces of a lens the spherical aberration can be minimised.
• A combination of concave and convex lenses can also reduce the spherical aberration.

2. Coma

The coma is a type of spherical aberration. It occurs due to the variation in the magnification of the image. The rays that are coming from an off-axial object and the rays pass through different circular zones of the lens. Due to this the image will appear in a comet-like shape. So, this aberration of the lens is known as a coma.

Types of coma

The coma varies due to the magnification of different zones of the lens. There are two types of coma

1. Positive coma

When the lateral magnification of the outer zone is greater than the central zone, then the coma is said to be a positive coma.

2. Negative coma

When the lateral magnification of the outer zone is smaller than the central zone, then the coma is said to be a positive coma.

Correction of coma aberration:

• By bending the lens the coma can be corrected but not completely processed will only work in the case of a single lens.
• The coma can be corrected by the combination of lenses that are symmetrical and in the application of curvature type of lenses surface

3. Astigmatism

It is the most common defect that occurs in the eyes. In this defect, the front part of the lens or cornea has an irregular curve. So, when the light refracts by the retina it forms a blurry image. Astigmatism is caused when eyelids put pressure on the cornea. mostly these defects passed over generations from their parents.

Types of Astigmatism

There are two types of astigmatism. 

1. Positive astigmatism: This is an abbreviation for which a person suffered from a farsightedness defect of the eye. For convergent lenses, the transverse focal is greater than the meridional focal length. This type of astigmatism is known as positive astigmatism.

2. Negative astigmatism: This is an abbreviation for which a person suffered from a near sightedness defect of the eye. For divergent lenses, the sagittal focal is smaller than the meridional focal length. This type of astigmatism is known as negative astigmatism.

Correction for astigmatism aberration:

• The combination of concave and convex lenses can also reduce astigmatism.
• Using lenses with different radii of curvature helps to reduce astigmatism.

4. Curvature of Field

When the central part of the image is flat but the exterior part of the image is curved concerning the object then this type of aberration in the image is called curvature of field. The curvature of the field arises when the paraxial focal length is greater than the marginal focal length.

Correction for the curvature of field:

• The condition for no curvature is known as the Petal condition. When the image of the plane object projects on the Petal surface the aberration gets reduced.

5. Distortion

The type of aberration in which the shape of the image gets distorted in the transverse plane as a whole is known as distortion. It arises due to the variation in the lateral magnification with the lateral distance of an object from the lens distance. 

Types of distortion:

There are two types of distortion

1. Barrel distortion: If magnification decreases with axial distance then the image of a square takes the form resembling a barrel. This type of distortion is known as barrel distortion.

2. Pincushion distortion: If the magnification increases with lateral distance, then a square’s image takes a shape like a pin-cushion. This type of distortion is known as pin-cushion distortion.

Correction of the distortion:

• A combination of two lenses can help us to avoid distortion.
• Using both barrel distortion and pincushion distortion combination to cancel out each other’s effect.

6. Chromatic aberration

When the images are formed by the refraction of white light, As a result, the image becomes colored. This type of defect in the image is known as chromatic aberration. This phenomenon occurs due to the dispersion of the white light.

Types of chromatic aberration:

There are two types of chromatic aberration

1. Lateral chromatic aberration: In this aberration, all the light rays concentrate at the same plane but different points.

2. Longitudinal chromatic aberration: In this aberration, the light rays of different wavelengths concentrate at different points along the principal axis (horizontal line) of the lens. 

 Correction of the chromatic aberration:

• Lateral chromatic aberration gets reduced when the object is placed at infinity.
• The combination of two lenses also reduces chromatic aberration.
• Achromatic lenses can be used to reduce chromatic aberration.

Axial color

Axial color is a phenomenon of aberration in which the position of the image shifts as the light wavelengths differ. Color fringing occurs due to color aberration. This aberration is caused by the light rays having different wavelengths to focus at various points.

Summary 

For non-paraxial rays, the actual image differs from the result of the paraxial approximation. This defect of the image is known as an aberration. For monochromatic light or single-wavelength light, there are five types of aberration. It is impossible to eliminate all kinds of aberrations by using a single lens. We can use different lens combinations to eliminate them.

Frequently Asked Questions

Q1. What is a spherical aberration?

Ans: The spherical aberration is the defect of the image in which central and peripheral incident rays from images at different points on the axis, are known as spherical aberration.

Q2. How to correct the coma aberration?

Ans: Coma can be corrected by bending the lens. This process will only work in the case of a single lens.

Q3. What is the one difference between chromatic aberration and spherical aberration?

Ans: Chromatic aberration is shown by white-colored light but the spherical aberration is shown by monochromatic lights.

Q4. What is the principal axis?

Ans: The principal axis is the axis that passes through the focus and center of curvature of the lens.

Q5. What is a positive coma?

Ans: When the lateral magnification of the outer zone is greater than the central zone, then the coma is said to be a positive coma.

Q6: White light is the polychromatic source of light. Explain why?

Ans: white light is the polychromatic source of light because it constitutes seven colors and each of them has a different wavelength.

Introduction

Let’s start with a fascinating experiment that you may have witnessed in your daily life. Insert a pencil or pen into a beaker of water. When you look at the pencil from outside the beaker, what do you notice? It will show up where it shouldn’t be, as you’ll discover. As a result of light refraction, this has happened.

It’s interesting to note that this occurrence is not just in water. You would see something similar if you were to use oil or any other liquid. A light ray changes direction whenever it crosses the boundary between two materials with different refractive indices. Remember that a material’s refractive index measures how quickly light passes through it in comparison.

It’s also fascinating to notice that refraction can occur even in a single medium. This is due to the fact that a substance’s refractive index alters with its density. The refractive index of a material increases with the proximity of its constituent parts. As a result, for instance, air density varies with altitude, causing light to bend as it travels through the atmosphere, a process known as atmospheric refraction.

Definition of Refraction

Refraction is the shift in a wave’s direction of propagation brought on by an inhomogeneous material. Refraction is most frequently seen in light waves. This indicates that refraction occurs anytime it comes into contact with an inhomogeneity along the way. Light can therefore “bend” when passing through the interface of two different media or when propagating across a non-uniform medium.

You can see in the accompanying diagram that the light, which would have normally followed the blue line, became distorted and ended up following the red line. The initial light ray, shown in grey, is referred to as the incident ray, while the light ray in red is referred to as the refracted ray. Which way does light bend next? is a question that might come to mind. The solution is a generalisation: light bends toward the surface normal if the second material’s refractive index is higher. If not, it refracts differently from the norm. The difference in the media’s refractive indices determines the degree of bending.

Definition of Atmospheric Refraction

The phenomenon of atmospheric refraction occurs when light from space that enters the atmosphere travels in a curved path rather than a straight line. This intriguing finding has a simple explanation for its origin. It is well known that air does not have a constant density. It alters with height instead. As a result, the refractive index is lower near the top of the atmosphere, where air molecules are further apart. The refractive index rises when density falls, and vice versa.

Atmospheric Refraction

Light continuously bends while propagating through our atmosphere as a result of this gradient-like characteristic, leading to a curved path rather than the expected straight line. You can see in the image above how the blue light rays take a curved course as they move through the various layers of air.

The explanation for Advanced Sunrise

Not all of the sunlight that strikes the earth’s atmosphere is absorbed by it. It is somewhat reflected in space. Think of viewing Earth from the international space station. You’ll notice that it seems brilliant and sparkling as a result of the earth’s atmosphere reflecting sunlight. Atmospheric reflection is the term for this phenomenon. Let’s talk about two typical consequences of atmospheric refraction: an earlier sunrise and a later sunset.

In the summer, sunrise in New Delhi, the capital of India, happens about 05:30 AM. On the other hand, if you were to stand on a rooftop and face east, you would notice that the sun rises roughly two minutes earlier. Why does that happen? Spend a moment trying to guess the solution.

The explanation is quite straightforward. The sun must be at a certain height above the horizon for light beams from it to reach your eyes, which can only happen when the sun is visible. because air’s refractive index varies, which causes the light to travel in a curved path.

Since sunlight falling on the atmosphere continuously bends as it reaches the earth, you may see the sun even when it is just below the horizon. The sun is not actually in the position it appears to be in when you view a sunrise. Simply put, it just appears a little higher due to the curve in the path of the sun.

The explanation for Delayed Sunset

The sun has set, which means that you can no longer see it. It has descended so low on the horizon, in other words, that light cannot enter your eyes anymore. However, even after the sun has passed the horizon due to atmospheric refraction, sunlight is still visible for a few minutes. We refer to this as a delayed sunset. As with advanced sunrises, the curved path of sunlight in the atmosphere is the cause of delayed sunsets as well.

Summary

Refraction is defined as the change in direction of propagation of light when it encounters a change in refractive index. It is observed whenever there is some sort of inhomogeneity in the medium or the path of light. When light moves in the direction of an area with a higher refractive index, it bends in the direction of the normal. Our atmosphere’s refractive index is higher close to the earth’s surface than it is farther away because it also contains a density gradient. Thus, as light travels to the earth’s surface, it continuously curves into a path. The term for this is atmospheric refraction. The sunrise appears to happen a few minutes earlier than usual due to atmospheric refraction. Similar to this, the sun is still visible after it has actually crossed the horizon, delaying sunset. Both of these events take place because atmospheric refraction makes the sun appear to be a little bit higher in the sky than it actually is.

Frequently Asked Questions

1. State the laws of refraction.

Ans. When light passes from one medium to another medium with different refractive indices, two laws of refraction are followed:

1. The incident ray, the refracted ray, and the surface normal all together lie in the same plane.

2. The ratio of the sines of angles of incidence and refraction is equal to the ratio of refractive indices of the materials.

2. By what amount does light bend due to refraction?

Ans. According to the second law of refraction also named as Snell’s law, we can write a relation between the incidence and the refraction angles, such that,

$$
\frac{\sin \theta_i}{\sin \theta_r}=\frac{n_2}{n_1}
$$

Therefore, if we know the angle of incidence and refraction, and refractive indices of the two different mediums, we can calculate the angle of refraction. 

3. What other phenomena occur due to atmospheric refraction?

Ans. The phenomenon of mirage and twinkling of stars are the two very common natural examples of the effects of atmospheric refraction. 

4. Does the amount of refraction depend upon the colour of light?

Ans. Yes, the refraction of light depends upon the wavelength, and the colour of light depends upon the frequency. The refractive index that a beam of light “sees”, or “experiences” depends upon its wavelength. 

5. Which colour of light bends the most?

Ans. The Cauchy’s equation, refractive index $$
n=A+\frac{B}{\lambda^2}+\frac{C}{\lambda^4}+\ldots,
$$

where λ is the wavelength of light, and A, B, and C are constants. Thus, from the above formula we can speculate that the light of smaller wavelength, or higher frequency will bend more. This corresponds to violet light in the visible region, which bends the most.

Introduction

An accelerometer is a tool used to measure the acceleration of a body. We are able to monitor and analyse both linear and angular acceleration using the accelerometer’s sensor. This function is used by us in many aspects of daily life and is a requirement for many fundamental systems and gadgets. An accelerometer, which measures numbers in one, two, or three planes, can be used to measure the acceleration force, or “g.” When the threshold is reached, a routine may start. Capacitive accelerometers, piezoelectric accelerometers, and piezoresistance accelerometers are the three basic types of accelerometers. Both inertial navigation and guidance systems make extensive use of them.

What is an Accelerometer?

An accelerometer is a sensor that allows us to track both linear and angular acceleration. This function is used by us in many aspects of daily life and is a requirement for many fundamental systems and gadgets. Static forces and dynamic forces are the two categories into which acceleration forces are divided. Static forces are those that can be constantly applied to an object, such as friction or gravity. Dynamic forces are those that can be described as “moving” and are applied to the object at various rates (for instance, vibration).

How does an Accelerometer work?

• The accelerometer operates on a very straightforward principle. An accelerometer, which measures numbers in one, two, or three planes, can be used to measure the acceleration force, or “g.”
• If the threshold is exceeded, it can trigger a routine. 
• The three-axis accelerometer, which features a system made up of three different accelerometers, is the most often used type of accelerometer. Each one calculates the acceleration in the X, Y, and Z planes in a separate direction.
• One of the popular models of a 3 axis accelerometer is the OKYSTAR OKY3230 type. The accelerometer will only estimate the force of gravity as the standard when it is in a stable position, which is when there is no external acceleration experienced by the accelerometer.
• Now, if we take a look at a three axes accelerometer and put it in a position where the sensor on the X axis points in the left direction, the Y axis points down, and the Z axis points forward, then the accelerometer will present the reading that is as follows:

$X=0 g, Y=1 g, Z=0 g$

Purpose of accelerometer

An accelerometer is a device used in vehicles to measure the acceleration motion brought on by either motion or gravity. The accelerometer’s primary function is to transform mechanical motion into electrical impulses.

Capacitive accelerometer

A capacitive accelerometer measures an object’s acceleration by monitoring changes in electrical capacitance. The most popular accelerometer is this one.

• Comparing the capacitive accelerometers to the other two types of accelerometers, they are the smallest and least expensive.
• Its name implies that it is a micro-electro mechanical system, and its parts range in size from 1 to 100 micrometres.
• The primary mechanism by which the capacitive accelerometer operates relies on the movement of a known mass suspended on springs. The mass is attached to one end of the spring, and the capacitor is attached to the other.
• When the sensor is subjected to a force, the mass moves, changing the capacitance of the capacitors and, in turn, the distance between their plates.
• However, for a variety of high amplitude signals and frequencies, this accelerometer’s accuracy is lower than that of other types of accelerometers.

Piezoelectric accelerometer

Using the piezoelectric effect, piezoelectric accelerometers can identify changes in acceleration.

• The working principle is similar to the piezoresistive one.
• When a material, often PZT, is subjected to acceleration, a deformation occurs that results in a change. But in this instance, it’s electric charge rather than resistance.
• Piezoelectric accelerometers have a very high sensitivity and accuracy, making them suitable for widespread application.
• They can be used for crash and impact tests in challenging conditions as well as for obtaining particularly sophisticated and accurate seismic estimation.

Piezoresistance accelerometers

As the pressure exerted on the piezoresistance accelerators increases, so does their resistance.

• As compared to piezoelectric accelerometers, these are far less sensitive.
• These accelerometers make use of the piezoresistive effect, a phenomenon that occurs when mechanical stress is applied and causes a change in a semiconductor or metal’s electrical resistance. An electrical signal is then produced by the accelerometer from the change.

Applications of accelerometer

An accelerometer is a piece of equipment used to measure a body’s acceleration. Both inertial navigation and guidance systems make extensive use of it. Other typical applications for accelerometers include:

• It plays a crucial role in the airbag deployment system of contemporary cars.
• It can be used to gauge seismic activity, vehicle velocity, or even inclination.
• It can be used to gauge how deeply to compress the chest during CPR.
• It can also be used to rotate the screen of a digital camera or a smartphone while displaying the images on the screen in an upright position.
• In a variety of modern electronics, accelerometers are crucial and active components.

Summary

An accelerometer is a sensor that allows us to track both linear and angular acceleration. The accelerometer operates on a pretty straightforward principle. An accelerometer, which measures numbers in one, two, or three planes, can be used to measure the acceleration force, or “g.” Capacitive accelerometers, piezoelectric accelerometers, and piezoresistance accelerometers are the three basic types of accelerometers. Accelerometers are used in a wide variety of scientific applications. The inertial navigation systems are most frequently used for aircraft or missiles.

Frequently Asked Questions

1. What is a gravimeter?

Ans: An accelerometer is known as a gravimeter when it has been expressly designed to be used in gravimetry, or to measure gravity.

2. What is the most common use of accelerometers?

Ans: Accelerometers are used in a wide variety of scientific applications. The inertial navigation systems are most frequently used for aircraft or missiles.

3. What are MEMS accelerometers?

Ans: Micro-electromechanical systems, or MEMS, are able to sense vibrations even at extremely small scales. To track changes in these electrical devices’ positions, they are mostly employed in a variety of portable gadgets.

4. How can an accelerometer be used for hard drive protection?

Ans: When a device experiences excessive acceleration or vibration, an accelerometer can identify it. It safeguards the hard disc in this case by emptying the reading heads to prevent contact with the pattern.

5. What are the key characteristics we need to keep in mind while selecting an accelerometer?

Ans: The sensor bandwidth, sensitivity, frequency response, and dynamic range of an accelerometer are some of the important properties we must take into account for a particular application.

Introduction

A conductor’s ability to resist the flow of electric current through it is known as resistance. Resistors are parts that are used to stop the flow of electrons. Due to the attraction between positive particles and negative electrons, the positive conductor particles obstruct the passage of electrons. The flow of electricity is resistant as a result of this obstruction. Ohms are the units used to measure resistance. There are two categories of electrical resistance: static resistance and dynamic resistance. The length of the conductor, cross-section area, temperature, material, etc. are the parameters that affect or depend on resistance.

Resistance of Conductor

Resistance is defined as a conductor’s ability to obstruct the passage of current. The conductor’s resistance is expressed mathematically as the relationship between the current flowing through it and the potential difference along its length.  The movement of electrons across a conductor is known as electric current. Because of their attraction to one another, positive conductor particles obstruct the flow of electrons, which results in resistance to the movement of electricity. Resistance can be used to disperse voltage in a current as well as control the flow of electrons.

The resistivity of the conductor depends on

The ability of a material to resist electrical conduction is known as its resistivity. Resistivity is utilised to offset the effects of size on resistance. It is a non-size dependent material attribute. The resistivity of a conductor is influenced by elements such as temperature, alloying, cold work, age hardening, and mechanical stress. For most materials, resistance rises with temperature. Semiconductors are an exception, as their resistance increases with temperature.

Resistance also depends on the temperature of the conductor. As the temperature increases the resistivity increases.

\[R{\rm{_T}} = {\rm{ }}R{\rm{_0}}(1{\rm{ }} + \alpha \Delta T)\]

R = final resistance, \(R_0\) = initial resistance, and α = temperature coefficient 

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Resistance depends on temperature

The thermal energy of electrons rises with the temperature of metal conductors, which also raises the frequency of collisions between free electrons. As a result, they begin to move randomly, making it challenging to drift for conduction in a specific direction. The conductor’s resistance increases as a result. As a result, resistance rises as temperature rises for a metal conductor. Increasing current frequently results in temperature rise.

Conductor resistance formula

The resistance of a conductor is directly proportional to the length of the conductor (l). Thus, on doubling its length, resistance will be double, while on halving its length, resistance will be half. Also, the resistance of a conductor is inversely proportional to its cross-section area (A).

Since, \[R\propto L\]

And, \[R\propto \frac{1}{A}\]

Hence, \[R\propto \frac{L}{A}\]

Or, \[R = \rho \frac{L}{A}\]

Where R is resistance in ohm, L is length or conductor in meter, A is cross-section area in square meter and ρ is the resistivity constant in ohm per meter.

The bigger the value of resistance, the more it opposes the current flow. The value of resistance is given in Ω.

Temperature effect on resistance

A material’s resistivity changes with temperature. Resistance varies depending on the conductor, semiconductor, and insulator’s temperature. Resistance is influenced by temperature in two different ways: for metal conductors, it rises as the temperature rises, and for insulators, it falls as the temperature rises. At high temperatures, semiconductors have great conductivity.

Problem 1: What is the resistance of the circuit having length 10 cm and area 100 cm$^2$ having resistivity of 1.8 Ω.m?

Solution:

Length of circuit = 10 cm

Area of circuit = 100 cm$^2$

Resistivity = 1.8 Ω.m

The Formula used,

\(R = \rho \frac{L}{A}\)

\(\Rightarrow R = 1.8~\Omega.cm \frac{10~cm}{100~cm^2}\)

\(\Rightarrow R = 0.18~\Omega\)

Problem 2: What is the cell constant of the circuit when the conductivity is 20 Siemens/m having resistance 100 Ω?

Solution:

Resistance = 100 Ω

Conductivity = 20 Siemens/m

Cell constant =?

The Formula used,

\(R = \frac{Cell Constant}{Conductivity}\)

\(\Rightarrow Cell~Constant = Conductivity \times R\)

\(\Rightarrow Cell~Constant = 20~Siemens/m \times 100~Ω\)

\(Cell~Constant = 2000~m^{-1}\)

Frequently asked questions

1.What is the importance of resistance in electricity?

Ans: Resistance is a crucial component of electrical circuits; as resistance increases, current flow becomes more challenging, and as resistance decreases, current flow becomes easier. The resistance is a crucial component in conduction. Conduction greatly benefits from electron flow. The conductor turns into a semiconductor and an insulator as a result of an increase in resistance.

2. Do conductors have high or low resistance?

Ans: Insulators have a very high resistance to electrical current, compared to conductors’ extremely low resistance. Resistance turns become an insulator as it rises. Since there is no interruption to the high flow of electrons, the conductor’s resistance is very low. Conduction and resistance are inversely correlated.

3. Is it a light bulb resistor?

Ans: Despite not actually being resistors, light bulbs exhibit resistive behaviour. Electrons cannot pass through resistors, which also transform energy into another form. The process by which electricity passes through a light bulb to produce light and heat is the same. The light bulb’s filament serves as a resistor. The law of conservation of energy states that as energy cannot be created or destroyed, it can only be transformed from one form to another.

Introduction

Natural fibres are fibres derived from plants and animals that have a wide range of applications in the production of composite materials. Most natural fibres are thought to be effective sweat and moisture absorbers, and different natural fibres can provide a wide range of textures.

What are Fibres?

Fibres are materials used in the production of textiles such as clothing and cables. All textiles contain natural or synthetic fibres. Natural fibres are made from natural sources such as animals and plants. Synthetic fibres are created through chemical synthesis.

Types of Fibres

1. Synthetic Fibres

Synthetic fibres, also known as man-made or artificial fibres, are manufactured through chemical synthesis and were first developed in the nineteenth century.

2. Natural Fibres

Natural fibres are derived from animals and plants, and they are frequently treated and spun into yarn before being turned into a product.

Examples of Natural Fibres

1. Cotton is derived from cotton seeds and is widely used in textiles. It is extremely lightweight, making it an ideal fibre for garment fabrics, and this has increased consumer demand.
2. Silk is derived from an insect and is the material used to make a cocoon.
3. Jute is a stronger fibre than cotton and jute, derived from plants, and it is used to make sacks and other packing materials.
4. Wool is derived from sheep and other hairy animals and is used to make fabrics due to its ability to retain heat. Wool is also a popular clothing fibre because it is preferred by people who live in cold climates.

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Advantages of Natural Fibres

1. Natural fibre clothing is significantly more pleasant to wear than synthetic clothing, especially during the summer, when people sweat more and just need clothing made of breathable materials that can soak the extra water.
2. Natural fibres are excellent insulators because they can trap air between them, preventing them from escaping into the atmosphere. This air, which is captured in the fabric’s microscopic holes, provides warmth and helps keep a person’s body temperature constant even in cold weather, which is why many skiers, hikers, and other people who live in cooler environments prefer to wear silk or wool.

The disadvantages of Natural Fibres

1. Natural fibres are generally more expensive than synthetic fibres due to their qualities as a wonderful insulator, being much more sustainable, and much more comfortable to wear, and because they are retrieved directly from the environment, the cost of producing them is often higher than the price of producing synthetic fibres.
2. Natural fibre production is not always completely under human control, and nature is autonomous and does not work by human requirements and aspirations. Natural disasters and tragedies have a significant impact on availability, causing significant variations in supply and price.

Summary

Natural fibres can be derived from both plants and animals and are used in a wide range of composite material production processes. Wearing natural fibre clothing is more comfortable than wearing synthetic fibre clothing. Synthetic fibres, which are produced through chemical synthesis, are also referred to as artificial fibres. 

Frequently Asked Questions

1. Why are natural fibres such good insulators?

Ans. Natural fibres can trap air between them, preventing them from escaping into the atmosphere. Even in extreme cold, the trapped air keeps a person warm and regulates their body temperature. Because of this, natural fibres are said to be excellent insulators.

2. Why are synthetic fibres so simple to make?

Ans. Synthetic fibres can be produced in greater quantities and at a lower cost than natural fibres, as well as faster in a factory.

3. What advantages do cotton fabrics have over synthetic fabrics?

Ans. Synthetic fibres are not suitable for hot and humid conditions because they do not absorb sweat as well as cotton garments, but cotton garments do. The cotton cloth absorbs water quickly and burns at a low temperature.

Introduction

Fossil fuels are hydrocarbon (compounds of carbon and hydrogen)-containing substances that form naturally (in nature) on the earth’s surface (earth’s crust). They are made up of the remains of dead (not alive) plants (flora) and animals (fauna) that are extracted (absorbed) and buried under the soil before being burned as fuel. Coal, petroleum, and natural gas are examples of well-known and widely used fossil fuels (or fuels). Coal seams are rock strata (stone) that form coal (charcoal) seams. When dead (not alive) plant matter (flora) decays (decomposes) into peat (an accumulation of partially decayed organisms), it is converted (transformed) into coal (charcoal) by heat (H) and pressure (P).

There are four stages involved in coal generation or formation: 

1. Peat 
2. Lignite 
3. Bituminous 
4. Anthracite

These stages (steps) are determined by the conditions in which they were buried. Coal has many applications in our lives, including home and commercial heating, the production of medicines and tars, and so on. Petroleum (also known as crude oil) is formed or produced from the decomposing remains of ancient marine organisms like bacteria, plants, and algae. Petroleum is used to produce heat and electricity, as well as a lubricant.

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What exactly are fossil fuels?

Fossil fuel is a type of hydrocarbon-containing substance that occurs or is produced naturally on the earth’s surface from the dead remains of plants and animals, which are extracted and burned as fuel. Coal, petroleum, and natural gas are three of the most common and widely used fossil fuels. Fossil fuels are sometimes burned to provide heat for direct use in cooking and heating. Additionally, fossil fuels are used to power engines and generate electricity.

The anaerobic decomposition of buried dead organisms containing organic-type molecules generated by photosynthesis is the origin of fossil fuels. And the conversion of these substances to fossil fuels necessitates or is the result of a geological process that takes millions of years. Fossil fuels are extremely important for humanity and development because they can be easily burned in the open atmosphere to produce heat. However, the excessive use or exploitation of fossil fuels by humans is also very harmful to the environment.

How Is Coal Made?

Coal is a black, solid, combustible fossil fuel. Coal contains a significant amount of carbon. Coal formation is a slow and gradual process that takes millions of years. And coal formation begins or begins in muddy wetlands where groundwater is near or slightly above the topsoil. Because of this condition, the flora presents there produces organic matter at a faster rate. The layers of organic materials are then accumulated and buried. These layers combine to form coal. The energy in coal is derived from sunlight, which is harvested by dead plants.

Although there are two major stages in the formation of coal, they are peatification and coalification. Peat (accumulation of partially decayed organisms) formation occurs as a result of bacterial activities, and the main factors in coalification are exceeding temperature and pressure from burial.

Coal Formation Stages

There are four stages in the coal formation and, they are peat, lignite, bituminous, and anthracite. These stages are determined by the conditions to which the remains (plant) are subjected (forced) after being placed inside or buried. The higher the ranking of coals, the greater the amount of heat and pressure applied.

1. Peat is the first stage in the formation of coal. In general, plant matter is oxidized to carbon dioxide (CO2) and water (H2O). However, if plant materials accumulate underwater (inside the water), oxygen (O2) is not available or present, and only partial (slight) decomposition occurs. This incomplete (partial) destruction (decomposition) results in the accumulation of peat, an organic (natural) substance (material).
2. The lignite-The second stage of coal formation, in which peat (first step) is subjected (forced) to increase vertical pressure (p) from collecting sediments. It is widely available, but it is only used as coal when a more (higher) efficient fuel (fossil) is unavailable.
3. Bituminous-The third stage in the formation of coal. Adding pressure, compacting (small area), and virtually (mostly) all traces of flora (plant life) have vanished or vanished. This type of coal can be found in Cape Breton and is also present in our most abundant fuel.
4. Anthracite-This is the fourth and final stage in the formation of coal. This is also known as ‘hard coal,’ because it is hard (strong) and has a high luster. The combination of high pressure and temperature causes this to form.

Coal Applications

1. Coal is used for a variety of purposes, including domestic and industrial fuel.
2. Electricity is generated or produced using this device.
3. It is also used as a fuel in automobiles.
4. It is used in the manufacture or preparation of cement, carbon fibers, medicines, and other products.
5. Furthermore, it’s also used in the steel industry to make steel and other metals.

Summary

Fossil fuel is a type of hydrocarbon-containing substance that occurred or is produced naturally on the earth’s surface from the dead remains of plants and animals, which are extracted and burned as fuel. Coal, petroleum, and natural gas are three of the most common and widely used fossil fuels. Fossil fuels are sometimes burned to provide heat for direct use in cooking and heating. Additionally, fossil fuels are used to power engines and generate electricity.

Frequently Asked Questions (FAQs)

1. What exactly do you mean by “fossil fuels”?

Ans. Fossil fuels are hydrocarbon-containing substances (materials) that formed naturally (in nature) on the earth’s surface (earth’s crust). They are made up of the remains (leftovers) of dead plants and animals that are extracted, buried, and burned as fuel.

2. What causes the production of fossil fuels?

Ans. The anaerobic (in the absence of oxygen) decomposition of buried dead organisms is the origin (point of generation) of fossil fuels (plants or animals).

3. Name the stages of coal formation.

Ans. The four stages of coal formation are peat, lignite, bituminous, and anthracite.

Introduction

There is matter in our universe. The matter is anything that maintains a quantity and a space. These things have a fundamental unit that cannot be divided into other parts with various chemical and physical properties. An atom is this fundamental component. An element is a substance that only contains one type of atom. Therefore, the species made up of a specific atom are the elements. For instance, there is only one type of atom in pure platinum metal. The atom was once thought of as an indivisible unit, but now it can be divided, releasing a huge amount of energy in the process.

Define an Atom and Molecule

An atom is the tiniest component of matter. The physical and chemical characteristics of the atoms that make up an element are all the same type. An atom is mono-nuclear, meaning that it has just one nucleus, which is surrounded by electrons and houses protons inside the central mass of the atom, the nucleus.

Chemical bonds bind the minimum required number of atoms in a molecule together. It is the joining of various atoms with the assistance of a chemical bond. The molecule oxygen\(\;({O_2})\) is a diatomic homo nuclear structure made up of two oxygen atoms bound together by a covalent bond.

What is the size of an Atom?

Only an estimation of an atom’s size can be made because it is impossible to measure it precisely. However, an atom’s atomic radius determines its size. Atomic radius is calculated by dividing the distance between adjacent atoms in a compound by two. Radii come in a variety of forms, including metallic, covalent, and ionic radii. The metallic radius is the separation between adjacent atoms in a metal. The covalent radius is the separation between adjacent atoms in a covalent compound. Ionic radii are the distances between adjacent ions in an ionic compound.

How atoms are formed?

The atom is the smallest unit of matter, consisting of a nucleus and electrons. The nucleus is the central portion of the atom that contains the positively charged proton and neutral neutron. And is surrounded by electrons that are negatively charged. Protons, electrons, and neutrons make up an atom. They are collectively known as subatomic particles.

Forces between Atom and a Molecule

Molecules are formed when atoms are held together by a strong chemical bond. These bonds are formed by the interaction of an element’s valence electrons to complete the octet. Chemical bonds are classified into several types. They do,

1.Ionic bond: When two atoms approach each other and have a large electronegativity difference, electrons, and anion forms are accepted. And the one that lost an electron will become an anion. An Ionic bond is formed as a result of the attraction caused by the positive and negative charge.

2.Covalent bond: When atoms with similar electronegativity differences approach each other, they share electrons. And this is a covalent bond.

Summary

Chemistry’s fundamental terms are atoms and molecules. Atoms are the fundamental building blocks of elements. A molecule is formed by the combination of different atoms using a chemical bond. These bonds could be covalent or ionic. Protons, neutrons, and electrons make up an atom. The size of an atom cannot be calculated precisely; only an approximation of size is possible. 

Frequently Asked Questions 

1. What exactly are isotopes?

Ans. Isotopes are atoms with the same atomic number but different mass numbers. The same atomic number denotes the same number of protons. And a different mass number means a different neutron number.

2. What is the mass number?

Ans. The mass number is the sum of protons and neutrons added to an atom of a chemical element. Lithium, for example, has a mass number of 7. Lithium has 3 protons and 4 neutrons.

3. What is the chemical formula?

Ans. A molecular formula is an expression used to represent a chemical compound that is the simplest whole-number ratio of the composition of elements present in a molecule.

Introduction

Atomic orbitals are the three-dimensional spaces that surround the nucleus and are most likely to contain an electron. The atomic orbitals have been combined to create molecular orbitals. They obtain orbitals in quantum theory, some of which are electron shells in the s, p, d, and f configurations. Although orbitals come in a variety of shapes and sizes, their square can be used to estimate their size or even shape. A total of two, six, ten, or fourteen electrons could fit in the s, p, d, and f subshells, respectively. The particular arrangement of electrons within orbitals in such an atom determines the majority of the chemical compositions of that atom. Depending upon the energy over its electrons, every orbital class seems to have a distinct form. The s orbital has a spherical geometry. The p orbital has the form of a dumbbell, as well as 3p orbitals, which vary in their arrangement across a 3-dimensional axis.

Define Atomic Orbitals

Atomic orbitals are numerical values that provide additional details about the waveform of electrons that inevitably surround atom centers. In the fields of quantum systems and atomic theory, specific mathematical expressions are frequently employed to determine the likelihood of detecting an electron at even a specific area surrounding the nucleus of an atom. The term “atomic orbital” may also refer to the region above an atom’s nucleus where there is the greatest chance that a particular electron will become accessible. Several quantum numbers affect each atomic orbital’s characteristics:

Table of All Possible Atomic Orbitals, where the Value of ‘n’ Ranges from 0 to 5

What do you mean by Atomic Orbital Theory?

An atomic orbital is a statistical term that describes the location or even waveform behavior of such an electron in an atom in both atomic theory and quantum field theory. These electrons, each of which has a distinct spin quantum number s, can fit into any one of these orbitals up to a maximum of two. One such formula can be used to determine whether it is possible to find an electron inside the nucleus of any atom at any particular location.

Summary

Atomic orbitals seem to be the regions around the nucleus of an atom where electrons have often been observed at that particular time. This is a mathematical concept that characterizes the wave-like activity with 1-2 electrons in an atom. Electrons inhabit low-energy orbitals (near such nuclei) before electrons approach higher-energy orbitals. When there is an option of equal-energy orbitals, then occupy the orbitals freely as feasible. That filling of orbitals on its own is termed Hund’s law when applicable. Atomic orbitals are typically denoted by a series of digits as well as letters representing unique features of such electrons linked only with orbitals, including 1s, 2p, 3d, as well as 4f. Primary quantum numbers are values that further indicate levels of energy.

Frequently Asked Questions (FAQs)

1. Is it possible to have an orbital without an electron?

Ans. An orbital’s characteristics are more like the electron residing inside it. This is standard procedure, however irrational this could appear, to refer to ‘Empty orbitals.’ The characteristics of unoccupied orbitals are the same as those computed for electrons within them.

2. What is perhaps the greatest number of orbitals possible?

Ans. The values n=3 & l=1 indicate that it has been a 3p-orbital, however, the number \(f(m_{l}=0)\) indicates that it is indeed a \(3p_{z}\) in origin. As a result, the specified quantum number can only identify one orbital, namely 3p_z.

3. How do electrons fill orbitals?

Ans. According to the Aufbau principle, electrons first occupy lower-energy atomic orbitals before moving onto the higher ones. Based on this method, we may forecast the electronic structure of atoms and ions.

Introduction

While the number of protons is merely the atomic number, the atomic mass of an atom is the sum of both its protons and neutrons. The letters A and Z can be used to denote these. Since it offers the key to the element’s existence, the atomic number is the concept that deals with such a periodic table element. It is only after interacting with this particular proton, which is primarily referred to as this hydrogen isotope’s protium, that the atomic and mass numbers are the same. Keep in mind, in particular, that while the atomic number remains constant, the mass number could change due to the presence of multiple isotopes. The elements are arranged in numerical order by atomic number.

Define Atomic Number

The number of protons in the nucleus of an atom is the atomic number. This is denoted by the letter Z. The number of electrons that surround the nuclei is controlled by the number of protons. In a periodic table with ascending atomic numbers, compounds with similar chemical properties typically cluster in the same column. Different elements have distinctive atomic numbers. For example, all C atoms have an atomic number of sixes, whereas all O atoms have an atomic number of eights.

Define Mass Number

Rutherford proved that an atom’s nucleus, which is composed of protons and neutrons, contains perhaps the majority of the atom’s mass. The mass number refers to the total number of protons and neutrons in such an atom. Atomic mass units are used to measure this. To represent it, the letter “A” is frequently used. This has typically been accomplished by simultaneously adding both neutrons and protons.

For instance,\(Cl^{37}_{17} \) appears to have a mass number of 37. Its nucleus contains twenty neutrons and seventeen protons.

What is the difference between Valency, Atomic number and Mass number

Valency	Atomic Number	Mass Number
The greatest amount of electrons that even an atom could lose, gain, as well as share, in addition to getting stable is referred to as valency.	An atomic no. is the no. of protons that exist in such an atom.	The mass no. within an atom is the total of its protons as well as neutrons.
The electronic arrangement of such an atom could be used to evaluate its valency.	The mass number has always been less than the atomic no.	The atomic no. is always greater than that of the mass number.
The no. of atoms does not affect valency.	No. of neutrons in an atom does not impact its atomic no.	The no. of neutrons inside an atom seems to not affect the mass no.
The no. of electrons does have a direct relationship with valency.	The atomic no. of isotopes seems to be the same.	The mass number of isotopes varies.
Elements are classified as monovalence, divalence, and trivalence based on their valency.	Isobars with similar atomic no. cannot exist.	The mass no. of isobars would be the same.

Energy Levels of Atomic Orbital

When an electron reaches a certain energy level, it is more likely to be found in these regions than in other regions. Orbitals are the name for those sections. Orbitals with roughly similar energies have created sub-levels. The maximum capacity for each orbital is two electrons. The energy of such an electron in a specific atom may be determined solely by the primary quantum number. In order of increasing orbital energy are the following orbitals:

\(1s<2s=2p<3s=3p=3d<4s=4p=4d=4f\)

Summary

The mass number of an atom’s nucleus is an integer equal to the sum of the nucleus’ protons and neutrons. The atomic number, in contrast, is simply the number of protons. Even though their mass is so small compared to that of protons and neutrons, electrons are not counted when calculating mass because they have no impact on the value. The number of neutrons may change, even though the number of protons in such an element’s units remains constant. An electron appears to have very little mass. Therefore, an atom’s atomic mass is roughly equivalent to its mass no. The mass number represents the weight of an atom’s nucleus in atomic mass units.

Frequently Asked Questions (FAQs)

1. Is there a relationship between atomic mass and weight?

Ans: No, atomic mass is indeed the weight of an atom, while atomic weight denotes the weighted average of naturally produced elements.

2. Why does an atomic number refer to as a fingerprint?

Ans: The physical or chemical characteristics of an atom have been exclusively governed by the no. of electrons inside its nucleus, but often along with its nuclear charge: the nuclear charge would be an element’s specific “fingerprint,” as well as Z identifies the chemical components individually.

3. Why is it that a mass number is typically a whole number?

Ans: Since it is the total number of the particles, the mass no. is always a whole number. This varies from the atomic mass unit, which is well recognized, as well as written to 6 decimal points.

Introduction

The poet Coates Kinney attempted to capture nature’s calming and soothing aspect in the poem “Rain on the roof” He was fond of nature and has always written profoundly about nature. To illustrate the poem’s true meaning, he has used literary elements like personification and alliteration. This poem starts with a rainy day when the poet starts recalling the past days after the rain. He begins to remember the instances and phases of his childhood when things were easy and simpler. In this poetry, the rain comforts the poet. He thinks back fondly on his happy childhood and all the wonderful times that he enjoyed. His heart is filled with passionate music as the rain fell, and he thought fondly of his mother. He associated the rain with his mother’s love and affection, which is why it always made him happy. The poet misses his mother, who isn’t with him right now and recalls the feeling of being at home. He feels the hurt, clings to the pillow, and drifts off to sleep recalling his past. The pain he experienced throughout his life is described in the poem.

Summary

This poem expresses the poet’s feelings toward rain. The poem’s opening line describes the clouds that cause rain. Humid, black, and loaded with water, the clouds are on the verge of bursting. Like a blanket, clouds have covered the entire city. The clouds have covered the stars, making the sky appear gloomy while the rain represents the clouds’ weeping. The poet’s mood was depressed as a result of the weather, and the only thing that makes him happy is to lie in his bed, hear the raindrops tinkling and remember his joyful past. The poet is feeling lucky to be home.

In the second stanza of this poem, the poet hears the sound of rain on the roof which is resonating in his heart. He recalls his childhood when he hears the music. The poet is trying to see fresh dreams while still thinking back on his past memories. He portrays his view as a dreamy fantasy in the second stanza. He is seeing his childhood memories and forming a beautiful picture. He also recalls the beautiful memories of his ceased mother and feels both happiness and grief.

The poet is recalling his mother’s lovely memories in the third stanza. He recalls his mother’s warm embrace as he listens to the rain’s glittering. He can still feel her love for him and his siblings. He was warmed by the nice memories, but he was also filled with regret because his mother had passed away a few years earlier. The poet is making a connection between the sound of rain and feeling her mother’s love. The author is reflecting on his own childhood days which were the “golden years” of his life. Even though his mother was no longer alive, whenever he heard the rain, he went back and thought of those happy moments and simply lies on his bed, cuddles his pillow, and drifts off to sleep.

Conclusion

The poem is about the poet’s calming and joyous recollection that emerges after a rainfall. The poet is making a connection between the rain and his childhood memories.

He is remembering the good old days when he was a child and had his mother by his side. He gets emotional as he thinks of his mother. He recalls the affection and embraces she used to shower on him and his siblings.

Question

1. What do the following phrases:-Humid Shadows, Stary spheres, What a Bliss, A thousand dreamy fancies into busy being the start, A thousand recollections weave their air threads into woof mean?

Ans: The given phrases mean-

• Humid shadows-It refers to the dark clouds that bring rain
• Stary spheres- This refers to a star-filled sky.
• What a Bliss- The poet fills the blissfulness when it rains.

• A thousand dreamy fancies into busy being the start- It alludes to the poet’s many thoughts that he is imagining.
• A thousand recollections weave their air threads into woof-It stands for various loving memories that the poet has reconciled.

2. What does the poet like to do when it rains?

Ans: The poet enjoys lying on his pillow in bed during the rainfall and remembering happy childhood moments.

He makes an effort to recall his mother’s warm embrace and the loving golden years.

3. What is the single major memory that comes to the poet’s mind? Who are the “darling dreamers” he refers to?

Ans: The one single memory that the poet can recall is of his mother’s unconditional love. The poet’s siblings are referred to as darling dreamers.

4. Is the poet now a child? Is his mother still alive?

Ans: The poet isn’t a child, and his mother is not alive

5. When you were a young child, did your mother tuck you in, as the poet’s mother did?

Ans: Yes, my mother used to tuck me in at night when it rained.

6. Do you like rain? What do you do when it rains steadily or heavily as described in the poem?

Ans: Yes, I enjoy the rain. Usually, I notice the rain and experience the chilly breeze. I also enjoy listening to the sound of the rain when I sleep.

7. Does everybody have a cozy bed to lie in when it rains? Look around you and describe how different kinds of people or animals spend time, seek shelter, etc. during rain.

Ans: Not everyone has access to a warm bed during rain. Not everyone can afford the convenience of sleeping in a comfortable bed while it rains. Because their homes can flood, some people are terrified of the rain. Animals are likewise afraid of the rain and seek shelter.

Rain on the Roof Extra Questions

1. What does the roof symbolize?
Ans: We are referring to a metaphorical roof. It serves as the mental roof we place over our heads to protect us from potentially harmful things. Each of us has one of these “roofs,” while some have stronger ones than others.

2. What figure of speech is represented in the roof’s rain?
Ans: In the poem “Rain on the Roof,” the principal figures of speech include personification, hyperbole, alliteration, and visual imagery.

3. What is onomatopoeia in the poem rain on the roof?
Ans: The use of sound words to create a dramatic effect and auditory imagery is known as onomatopoeia. The employment of sound words such as “patter.” which represents the sound of raindrops hitting the roof’s surface is an example of onomatopoeia.