Category: Physics Notes PPT

You might come across the term ‘speed’ almost every day, no matter to which walk of life you belong to. Yet, what does ‘speed’ actually mean in terms of physics? Is it any different from the sense you generally use it in? Moreover, what is the SI unit of speed? This article will help you answer all the questions that you have in mind regarding this topic. 

In the field of physics, speed refers to the rate at which an object moves. More specifically, this term implies the distance that an object travels with respect to time. You witness moving objects daily, such as a car, a cycle, or even while walking. Thus, speed is the measurement of the distance that a body covers within a particular time. 

When a body covers greater distance within a specific amount of time, you can say that it has a high speed. On the other hand, when that very body covers a short distance at the same time, the speed is low. 

Calculating Average Speed

Average speed can be calculated by dividing the total distance the object travels by the total amount of time it takes to travel that distance.

While the speed of the object may vary during the total time it is moving, the average speed is the result of the total distance divided by the total time taken.

Speed measurements contain a unit of distance divided by a unit of time. Examples of units of speed might include “meters per second” (m/s), “kilometers per hour” (km/h), or “miles per hour” (mph or mi/hr).

Average speed can be calculated using the formula v=d/t where the variables are:

v is the average speed of the object with units of m/s

d is the total distance or length of the path of the object with units of m

t is the total time taken to cover the path with units of s

Speed cannot have a negative value.

Velocity (Speed and Direction)

Velocity refers to both the speed of an object and the direction of its motion.

A velocity value should have both speed units and direction units, such as m/sec north, km/h south, cm/s left, or km/min down.

If an object is moving forward, it has positive velocity. When an object is moving backwards, it has negative velocity.

When you throw a ball in the air, it has positive velocity. When it heads back towards you, it has negative velocity.

 

What is the SI Unit of Speed? 

Every measurement requires an SI unit so that it becomes easy to distinguish it from the rest. A simple numerical expression is ambiguous and vague, and it could mean a thousand things. Therefore, you will need a basic unit of speed that differentiates it from other measurements. 

Now, if you are asking what the basic unit of speed is, here is the answer – 

Meter per second is the SI unit of speed. This unit of speed signifies as to how many meters an object can travel within a second. Say, a body travels 10 meters in a second. In that case, the speed of the body is 10 meters per second. 

The SI unit of speed is written as m/s.

What is the Derivation of the SI Unit of Speed? 

Now that you know that speed is the distance that an object travels within a specific time, you must also note why the unit of speed is a derived unit. 

The definition of speed in mathematical terms is expressed by the following formula which is also used to calculate the same. 

ν = d/t

Where ” V stands for speed, ‘d’ means distance, and ‘t’ implies time. 

Suppose that an object covers 50 meters at a time of 5 seconds, then – 

ν = 50 metres/ 5 seconds = 10 meters/second or 10 m/s. Therefore, the SI unit of speed is 10 m/s for this object. 

Also, speed also possesses a dimensional formula, which is M0.L1.T-1.

You can also express the SI unit of speed in terms of the CGS system, or centimeter-gram-second system. In that case, cm/s or cm s-1 signifies the speed of a moving object. 

Wondering How to Convert m/s into cm/s or the CGS Unit of Speed? 

Suppose that an object moves 100 meters in 20 seconds. Consequently, the speed becomes 5 m/s. However for CGS unit, you will have to convert 100 meters into cms. 

1 m = 100 cm

Therefore, 100 m = 100 X 100 cm = 10,000 cm. Thus, the CGS expression of speed in this case becomes-

ν = 10,000 cm/20 seconds = 500 cm/s or 500 cm s-1. 

How to Calculate Speed?

Step 1: Place the constant velocity car in position on a surface, with plenty of space in front of it. Use the duct tape to mark the starting position of the car, placing a piece right behind the back wheels.

Step 2: Measure a distance from the tape, a few meters along the floor (longer is better), and place a second piece of duct tape. Note down the total distance.

Step 3: Turn on the motorized car, place it in position in front of the starting tape, and release it, starting the stopwatch at the same time.

Step 4: Stop the stopwatch when it reaches the second piece of tape, and note down the time in a data table that looks something like this:

Step 5: Repeat the experiment at least five times, and note down all the trials.

Step 6: Find the average of your five or more trials by adding up the numbers and dividing by how many trials you did.

Step 7: Calculate the speed of your car using the equation: speed equals distance divided by time.

Some Interesting Facts Related to Speed 

Keep in mind the following interesting facts involving speed – 

• The speed at which light travels is 299,792,458 m/s. 

• The speed of sound in dry air is 343.20 m/s. 

• You would have to travel at a speed of 11.2 km/s (or 11200 m/s) to escape the gravitational pull of our planet. 

Now that you know that the SI unit of speed is m/s, browse our website to learn even more about the intriguing properties of speed and other related concepts.

You can even download our app for an interactive and personalized learning experience. 

If we read the history of electronic devices, one of the most important components of these devices was a vacuum tube (electron tube). This tube was used to control the electric current. These tubes were larger, required higher operating voltage, high power consumption meant high heat generation which in turn affected the life of the tube due to its low efficiency.

On this page, we will learn about the following:

To resolve this problem, the three American physicists John Bardeen, Walter Brattain, and William Shockley invented a compact-sized and efficient semiconductor device called point-contact transistor at Bell Labs in December.

Transistor

A transistor is a kind of semiconductor that is used as a conductor and insulation of electric current or voltage. In simpler terms, a transistor is basically a regulator of the flow of electric signals. Read the following points to know more about transistor:

• Transistors are powerful devices because of their ability to control the current flowing through a circuit (current controlling device), which is generated by the flow of electrons and holes. There are two types: NPN (negative -positive-negative) and PNP (positive-negative-positive).

• The most widely used transistors are NPN transistors as the majority of charge carriers are electrons that are better mobile charge particles with less mass due to which they can easily accelerate.

• It is a semiconductor device that acts as a switch and an amplifier. Transistors can operate on a low-voltage supply for greater safety which means they yield higher efficiency and very long life.

• The transistors use semiconductor junctions instead of heating electrodes but perform the same function as a vacuum triode.

• The transistors can control the flow of current through one channel by changing the intensity of a small amount of current flowing via a second channel. That’s why they are called the current controlling device.

Parts of a Transistor

A transistor is a combination of three terminals made of semiconducting materials that help in making a connection to an external circuit and allow current to flow. The three terminals are:

1. Base: The base activates the transistor. It is thin and lightly doped. It is put in the centre of the transistor.

2. Emitter: The emitter is the negative terminal of the transistor. It is heavily doped and is moderately sized.

3. Collector: The collector is the negative terminal of the transistor. It is located on the right side of a transistor and is moderately doped. It is larger than the emitter.

How does a Transistor Work?

A Bipolar Junction Transistor or BJT consists of three terminals- base, emitter and collector. A p-n junction exists between base and emitter, and another junction exists between base and collector. Normally, in BJT when current flows through the base-emitter junction, a current will flow in the collector circuit. This is called bias and the base-emitter junction is forward biased whereas the base-collector junction is reverse biased.

Basics of Bipolar Junction Transistors

Since the controlled current must go through two types of semiconductors materials the current consists of both electron and hole flow, in different parts of the transistor, and these are of two types:

1. n-p-n junction transistor

2. p-n-p junction transistor

Isolated Gate Bipolar Transistor (IGBT): IGBT is a power semiconductor device used as an electronics switch in much high power and modern appliances such as electric cars, trains, variable speed refrigerators, air conditioning systems.

What are the Characteristics of a Transistor?

The characteristics of a transistor is the graph plotted for each type of configuration, which shows the relationship between the current and voltage of the transistor.

There are mainly two types of characteristics:

1. Input characteristics: This shows the change in input current with varying output current when the output voltage is constant.

2. Output characteristics: This graph shows a plot of changing output current with respect to a change in output voltage when the input current is constant.

Advantages of using Transistors

Transistor has been proven as a very important invention in science. It has many uses and advantages:

• It is small in size and is very cost-efficient.

• It needs very low voltage to function.

• It has a long life and requires no power to operate.

• A single integrated circuit can be developed using the transistor.

• Current switches fast in the terminals.

Limitations of using Transistors

Even though transistors are extremely efficient, there are some limitations to its uses:

• Transistors get damaged very easily due to changes in electrical and temperature conditions.

• They lack higher electron mobility.

• They can get affected by radiation.

Know more about transistors by visiting our website where you can find notes, questions, answers and solutions and more! You can download anything you need for free! 

Uses of Transistor

Vbe biasing voltage produced in the base-emitter junction. Due to the forward biasing of the base-emitter junction, the electrons start flowing from emitter to recombine with holes in the base, the base becomes negatively charged. If the base current Ib is increased by a small amount, hole-electron recombination will get neutralised, the collector current Ic will be increased. Therefore, a small change in current Ib in the base.

• Microphone: The microphone is a transducer that converts our voice or sound wave to an electronic signal. As the sound wave doesn’t have a constant value, the magnitude of the sound wave varies with time according to our voice.

The electrical output of the microphone varies according to the sound waves as the base current Ib is varying because of the small alternating voltage produced by the microphone which means a small change in Ib can cause a large change in Ic.

When this output of the microphone is given to the transistor as an input. The varying collector current Ic flows into the loudspeaker, and we know that if there are changes in the input of the transistor there will be a large change in the output of the transistor. Thus, the transistor amplifies the electronic signal of the microphone.

The frequency remains constant but the amplitude of the sound wave from the loudspeaker is higher than sound waves fed into the microphone.

An electronic oscillator is a device that generates continuous electrical oscillations. In a simple oscillator circuit, a parallel LC circuit is used as a resonant circuit and an amplifier is used to feed energy to the resonant circuit.

The frequency gets resonantly amplified, and the output acts as a source of an alternating voltage of that frequency.

• Transistor Used as a Switch
  BJT Transistors can be used as a switching device to control DC power to a load. The switched (controlled) current goes between emitter and collector, and the controlling current goes between emitter and base.

Summary

• In normal operation of a transistor, the emitter-base junction is always forward-biased whereas the collector-base junction is reverse biased.

• In n-p-n junction transistors, there are a large number of electrons in the emitter and a large number of holes in the base.

• In the actual design of n-p-n transistors, the middle layer is very thin (micrometre) as compared to the widths of the two layers at the sides.
  

A solar cooker is a very efficient device. It does not cause air pollution and saves the natural fossil fuel of the earth. This device uses solar energy to cook food. The concept behind this device is that a concave surface reflects and focuses the sun’s heat. The amount of heat is quite large to be able to cook the food. There are three hundred models of solar cookers presently. They range from absolute simple designs to very complicated and advanced technologies. Usually, the largest used solar cookers are simple to build and very cheap. Solar cooking is a solution for people who don’t have access to fuel for cooking. This technology is a boon for them. Moreover, the more we harvest solar energy for cooking, the more clean, fresh, and unpolluted air we breathe. The raw food items are cut into small pieces while cooking. The various uses of the cooker are:

• A solar cooker requires a limited quantity of water to cook the food. 

•  The water gets evaporated and then recaptured as freshwater. The solar ultraviolet rays kill the DNA linkages in microorganisms and hence purify the water. Thus water gets distilled.

• Iron ore smelting using solar power does not involve the emission of excess carbon dioxide into the atmosphere and hence is a clean process.

• We can dehydrate the vegetables and other food items in the solar cooker or oven.

• The solar wax melter is a simple solar oven. It has a screen on which we place the raw-wax. It melts slowly and drips into the container below it. 

• Specially designed solar cookers are used in hospitals and clinics to sterilize their instruments. The doctors prefer using this device as it reduces pollution.

The Three Main Principles of a Solar Cooker

A solar cooker can work only in the daylight. At night it is useless and cannot serve its purpose. There are three main principles based on which the heating takes place in a solar cooker. These are;

• The concentration of heat on an object can only occur faster when the sun rays (UV) focus at a particular point. The solar cooker has a reflecting surface made from shiny reflecting material. Metals like chromium, silver, and aluminium constitute these reflecting surfaces.

•  Black colour absorbs more heat than any colour. Light colours reflect heat. Therefore, most solar cookers are coloured black so that they can absorb more heat to cook well. Also, these cookers are thin so that the heat gets transferred quickly and uniformly to the food.

• The solar cooker should be able to trap the heat which it has absorbed. Otherwise, the heat will escape from the food. It will not cook properly. For this reason, the cooker has a lid that tightly covers it. 

Solved Examples

1. How to Trap Heat in a Solar Cooker?

The solar cooker uses heat energy from the sun to cook food. The heating of these cookers takes place using simple phenomena called specular reflection. The angle of incidence of the light beam, focussed on the cooker, is equal to the angle of reflection. This phenomenon requires a very smooth surface. No light is scattered away in another direction. This phenomenon used to focus on the maximum heat at a particular point.

2. What are the Advantages of Using a Solar Cooker?

There are various kinds of solar cookers. Using them has several advantages;

• Using solar energy for cooking reduces the carbon footprint as no carbon-based fuels or current from the electricity grid is used.

• Using less fossil fuel saves the cost spent behind it. It also reduces deforestation and keeps the environment clean.

• Cooking can be done at temperatures above 290 degrees celsius with the help of the vacuum tube and parabolic solar cookers.

• The conventional solar box cookers can reach up to temperatures of 160 degrees that helps in cooking most food items like bread and vegetables. It also helps in the sterilization of food and instruments.

In 1873, Johannes Diderik Van Der Waals derived the Van Der Waals equation. The equation is considered as the updated version of the ideal gas law that states that there are some point masses present in gases that undergo perfectly elastic collisions. However, the real gas law is incapable of explaining the behaviour of real gases. Due to this reason, the Van Der Waals equation was derived to define the physical state of a real gas.

The full name of Van Der Waals was Johannes Diderik van der Waals. He was a Dutch thermodynamicist and theoretical Physicist, who had won the Nobel prize in physics in the year 1910. And as you may have already understood by now, the Van der Waals equation is named after him, because he was the one who gave it.

The Van der Waals equation is the equation of state of thermodynamics, it is based on the theory that suggests that the particles with non-zero volumes, makes the fluids. Van der Waals derived it in 1873, based on the traditional set of derivations, which are also derived from the Van der Waals. The equation explains the condensation of the gases to the liquid phase. The equation was so impactful that another famous scientist of the time James Maxwell said that the name of Van Der Waals is going to be famous in molecular science.

Also, if you like to learn about the Van der Waals forces, then follow this link.

What is Van Der Waals Equation?

Van Der Waals equation is an equation that is used to relate the relationship existing between the pressure, volume, temperature, and amount of real gases. For a real gas containing ‘n’ moles, the real gas equation derivation is as follows.

(P + [left ( frac{an^{2}}{V^{2}} right )] ) V−nb = nRT

Where,

P is the pressure,

V is the volume,

T is the temperature,

n is the number of moles of gases,

‘a’ and ‘b’ are the constants that are specific to each gas.

The equation can be written as:-

1. Cube power of volume:

V³ – b+(RT/P) V² + ( a / P) V – ab / P = 0

1. Reduced equation (Law of corresponding states) in terms of critical constants:

           ( 𝜋 + 3 / φ²) ( 3φ– 1 ) = 8τ

Where:

𝜋 = [frac{P}{P_{c}}]

φ = [frac{V}{V_{c}}]

τ = [frac{T}{T_{c}}]

The units of Van Der Waals constants are:

For unit ‘a’ = atm lit² mol⁻²

For unit ‘b’ = litre mol⁻¹

Derivation of Van Der Waals Equation For Real Gases

It is easy to derive Van Der Waals equation for real gases but only if the right steps are followed. Any mistakes committed in the process to deduce Van Der Waals equation of state can be crucial and affect the whole process.

Let us discuss the process to derive the Van Der Waals gas equation.

In the case of a real gas when students are using Van Der Waals equation, the volume of a real gas is considered as (Vm – b), where b can be considered as the volume occupied by per mole.

Therefore, when the ideal gas law gets substituted with V = Vm  – b, it is given as :

P(Vm  – b) = nRT

Due to the presence of intermolecular attraction P was modified as follows.

( [frac{P+a}{V^{2}}] ) ( Vm  – b)  = RT

( [frac{P+an^{2}}{V^{2}}] ) ( V – nb) = nRT

Where,

Thus, it is possible to reduce Van Der Waals equation to ideal gas law as PVm = RT.

 

Van Der Waals Derivation For One Mole of Gas

To derive the Van Der Waals equation or to deduce the Van Der Waal equation of state for one mole of gas can be turned into an easy process if the right steps are followed.

The steps for derivation of the real gas equation for one gas are as follows.

p = RT / V = (RT / v) p = RT / Vm  – b

C = Na – Vm   (proportionality between particle surface and number density)

a’C² = a’ ( Na / Vm)² = a / Vm²

p = RT / (Vm – b) – a /  Vm²  =>  [ [ p + (a /  Vm²)] ] Vm−b = RT 

[ [ p + ( n²a / V²) ] ] V−nb = nRT

( substituting nVm  = V )

Derivation of Real Gas Equation When Applied to Compressible Fluids

Van Der Waals equation derivation, when applied to compressible fluids, can be understood if the concepts are clear.

Compressible fluids like polymers have fluctuating specific volumes and this can be expressed as follows.

(p + A)(V – B) = CT

Where,

P: pressure

V: Specific volume

T: Temperature

A, B, C: Parameters

All this above information is used to derive the Van Der Waals equation of state.

Merits and Demerits of Van Der Waals Equation of State

Merits:

• It can predict the behaviour of gas much better and accurately than the ideal gas equation.

• It is also applicable to fluids in spite of gases.

• The arrangement is made in a manner of cubic equation in volume. The cubic equation can give three volumes which can be used for calculating the volume at and below the critical temperatures. 

Demerits:

• It can only get accurate answers for real gases which are above the critical temperature.

• Below critical temperature results also get accepted.

• In the transition phase of gas, the equation is a failure.

Conclusion

More importantly, the Van Der Waals equation tends to take into consideration the molecular size and the molecular interaction forces which can be attractive or repulsive forces. Sometimes it is also known as Van Der Waals equation of state. In this article, students will learn how to derive the Van Der Waals equation of state.

Introduction

Communication is one of the great discoveries of human beings. It not only helps us to understand but also to express ourselves. This process of understanding and expressing is not only done by humans but also by animals, microorganisms too, but we definitely do it on a better level.

It establishes interconnectivity between individuals everyday. It even simply does not give us a pace to speak but express our different expressions e.g. crying , yelling, laughing , screaming , shouting , singing, and many more.

Vocal Cord the Source of Human Voice

We communicate by means of our voice which has different expressions and tone as well. For e.g. a new born baby’s tone can easily be understood though it cannot speak. A young boy’s tone can easily be recognised, an old man’s tone can easily be recognised, an  angry womens tone can be recognised, we can differentiate between the voice of a girl and a  boy.

All these tones and voices which we can easily differentiate are due to the vocal cord.

Scientists study shows that the twelve voice notes on which the maximum portion of music is based has got its base from human voice during the time of evolution.

The size of the larynx differs in different individuals.

This size differentiation basically denotes the difference in pitch of both the genders, where the females pitch is considered high as compared to the male .

E.g. a male voice has the bass, baritone, tenor and countertenor,  while the females voice possess contralto, mezzo soprano etc .

There are many folds in the larynx.

These get attached to the back side of the arytenoids, cartilages and at the front of the thyroid cartilages .There are no outer edges in the breathing tube while the inner one has full freedom to vibrate .

There are three layers within, them which are :

The epithelium layer, the vocal ligament and the muscles which is also known as the vocalis muscle .

Another feature they possess are the triangular bands that are pearly white in color.

Both sides of vocal cords have vestibular folds, other names for false vocal cords.

It  has small space between the folds as shown below:

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The sound which we produce is entirely different from others not only because of the shape and size of the vocal cord but because of the shape and size of the human body and its shape and size of the human body, especially the vocal tracks that become habitual the way we speak.

For producing different pace or tones of sound we could try doing things eg tightening or loosing our tongue or inflammation in lungs .

Any methods like this could result in the change of voice.

Now, that we know the importance of the vocal cord,  we must be aware of the diseases that occur in the vocal cord .

There are many disorders which can affect the human voice,  these are speech impediments ,   growths of vocal folds or lessening up of vocal folds at times vocal loading also gets inflicted on the speech organs.

Though There are remedies to these problems by vocal therapies or voice therapies .

The Main Parts of Voice Production

However,  we wonder that this beauty of expressing ourselves and understanding others is fitted inside us in a compact manner.

These are broadly divided into three types:

1. The first one is lungs which is also known as the power source.

2. The second subdivision is the voice box which is also known as vibrator or larynx.

3. The last ones are throat, nose, mouth and sinuses which are also known as the resonators or articulators.

Heading toward the 1st process of sound formation : the lungs ;

Now looking into the  process of working,  we will see that the lungs which are also the pump,  must produce an adequate amount of air flow and air pressure to vibrate the vocal folds or vocal cords.

The 2nd part is  larynx (voice box)

Larynx : it’s a structure on the top of the windpipe .

It is responsible for sound production.

Vocal folds : soft tissue which is the main vibratory component of the voice box.

Glottis :(also called rima glottidis): it opens between two vocal cords .

It opens during breathing and closes during swallowing.

Voice = sound +resonance +articulation.

A huge amount of air pressure is  sent towards the vocal folds

Diaphragm, abdominal muscle, chest muscle, rib cage, coordinates to move the air out of the lungs and towards the vocal chord.

Thereafter, the vocal folds vibrate which creates a sequence of vibratory cycles.

To the midline of the voice box vocal folds are moved by the help of muscles, nerves, cartilages.

This cycle repeatedly occur on vibratory cycle as as following:

Air pressure- : it opens vocal folds, air pressure continues to move in upward directions to the top of vocal folds and opens it’s top.

Closure of vocal folds-: it cuts off air pressure and releases a pulse of air.

The new cycle starts again after that..

These cycles produce voice stands which is a buzzy sound, it is then amplified by vocal tract resonators producing sound.

Diagram Depicting Sound Frequencies:

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(when Loudness is increasing- its known as amplitude and when frequency is increasing- then it’s known as pitch).

The third and the last part includes nose , pharynx, mouth, amplifying and modifying sound.

The muscles of the larynx have a tongue (lips, cheek etc) which filters the sound and articulates it from the larynx.

It allows to take different quality of voice’

E.g. a trombone player playing its instrument by mouth and as the slide is changed the sound automatically changes.

Light is the electromagnetic radiation that occurs within a specific section of the electromagnetic spectrum. The term essentially refers to the visible light, it is the light that is distinguishable and visible to naked human eye and it is also responsible for the sense of light. The wavelengths of the visible light range between 400-700 nanometers, this is between the infrared having longer wavelengths and the ultraviolet having shorter wavelengths. 

The wavelength of the visible light indicates that its frequency is approximately 430-750 terahertz (THz). The light speed in the vacuum is 299,792,458 metres per second as per the experiment. The visible light like other forms of the electromagnetic radiation moves at this speed specifically in the vacuum. In physics, the definition of light often refers to the electromagnetic radiation having any wavelength, regardless of if it’s visible or not. The forms of radiation such as radio waves, gamma rays, microwaves, and X-rays are all different forms of the light. 

The light exhibits both particle nature and wave nature and the occurrence of this phenomenon is described as light’s dual nature. Light exists in the form of particles and propagates in the form of wave. The study associated with light is called optics, and optics is an important domain in the study of physics. 

Light doesn’t necessarily travel in the straight line but it travels in transverse waves. The wave that is made of oscillation when moving and that occurs perpendicular to direction of energy transfer is known as the transverse waves. Wavelength is essentially the distance between two consecutive troughs or two consecutive crests in the transverse wave. The wavelength is also used for representing repeating pattern of travelling energies, like sound or light.

Wavelength:

We know that light can be understood both as a particle and a wave. Photons are the light particles which exist in the form of “packets” of electromagnetic energy. On the other hand, waves are the form of energy where electromagnetic radiation takes on when it is propagating.

Light does not travel in a straight light line. It travels in the form of a transverse wave. A wave which consists of oscillation while moving which occurs perpendicular to the direction of transfer of energy is called transverse waves. Wavelength is the distance between two consecutive crests or two consecutive troughs in a transverse wave. Wavelength also represents a repeating pattern of any traveling energies, such as light or sound. Wavelength is usually expressed by the units of nanometres (nm) or micrometres (µm). It is represented by the symbol λ which is read as lambda.

The frequency and Wavelength Relationship

The frequency and wavelength are closely associated with each other, especially in relation to light. Wavelength is the distance between two consecutive troughs or crests whereas frequency is defined by the number of waves which pass via a single given point within the specified period of time. The wavelength and frequency are inversely proportional which means the longer the wavelength, the lower is the frequency. The frequency tends to be higher when specifically the wavelength is short since more troughs and crests pass via the specific point when wavelength tends to be short. Conversely the frequency tends to be lower when wavelength exhibits a longer path.

Table of the Wavelengths of Various Colours, and Their Frequencies:

White Light: White light’s wavelength extends from 400 to 750 nm. When the white colour is passed through the prism, the light spectrum is formed due refraction of different wavelengths through different angles.

Ultraviolet Light: Ultraviolet light extends from the end of the visible region and the X-ray region in the electromagnetic spectrum. It gets its name as it is the light closest to the violet portion of the visible light and is in the range of 10 to 400 nm.

Infrared Light: Infrared radiation has a longer wavelength than visible light and is close to the red portion of the visible spectrum of light. It extends from 750 nm to 1 mm. Infrared radiation cannot be seen but can be felt in the form of heat.

Red Light and Orange Light: Red light and orange lights whose wavelength lies between 750 to 610 nm and 610 to 590 nm respectively are best viewed naturally during sunrise and sunset. This is because the associated wavelengths of red and orange from sunlight are not properly scattered by the atmosphere during these times.

Yellow Light: Yellow light has a wavelength between 590 and 570 nm. Yellow light is emitted by low-pressure sodium lamps.

Green Light: Green colour, whose wavelength extends from 570 to 500 nm, can be prominently seen in grass and leaves. Grass reflects green wavelength and absorbs all other wavelengths and thus appears green.

Blue Light: Blue light has a wavelength ranging from 500 to 450 nm. The atmosphere scatters shorter wavelengths efficiently and thus the wavelength corresponding to the colour blue is scattered efficiently by the atmosphere. That’s why the sky appears blue when we look up at it.

Indigo Light Violet Light: With a wavelength between 450 and 425 nm, indigo is a colour which is between the primary colour blue and the colour violet in the colour wheel. Violet with a wavelength of 425 to 400 nm is the visible light with the shortest wavelength. It has a shorter wavelength and is hence scattered more effectively by the atmosphere. But since our eyes are sensitive to blue colour, the sky appears blue rather than indigo or violet colour.