Tag: fibre optics basics

Questions Related to fibre optics basics

Line spectrum is obtained from the :

physics spectra sunlight - white and coloured sunlight - combination of 7 lights fibre optics basics

  1. Sun

  2. Filament of the bulb

  3. Mercury lamp

  4. Burning coal

Show answer
Correct Option: C
Explanation:

As a light source, we will use a mercury lamp, which emits light at several discrete wavelengths. The device we are using is called a prism spectrometer because, once the prism is calibrated, it can be used to measure the wavelengths of the lines in the spectra produced by various atoms.

A piece of cloth looks red in sun light. If it is held in the blue portion of a solar spectrum, it will appear

physics spectra sunlight - white and coloured sunlight - combination of 7 lights fibre optics basics

  1. Red

  2. Black

  3. Blue

  4. White

Show answer
Correct Option: B
Explanation:

A cloth piece looks red in sun light because it absorbs all the colours of sun light except red, red is reflected to our eyes.

When red cloth piece is held in only the  blue portion of solar spectrum, the blue light will be absorbed by red cloth and as there is no red light is to reflect, therefore no colour will be reflected back i.e. cloth piece will appear black.

Which of the following colours of light undergoes the least deviation while passing through a glass prism ?

physics spectra sunlight - white and coloured sunlight - combination of 7 lights fibre optics basics

  1. Red

  2. Blue

  3. Yellow

  4. Green

Show answer
Correct Option: A
Explanation:

Red goes through least deviation because it has highest speed among VIBGYOR.

We know,            $\nu\times \lambda=c$
   Frequency is a constant quantity.
also, 
                           $\mu=\dfrac{velocity\ of\ light\ in\ vacuum}{velocity\ of\ light\ in\ a\ medium}$
.

   so refractive index will be very less for red color and hence show least deviation.


The light which refracts most while passing through a prism is

physics spectra sunlight - white and coloured sunlight - combination of 7 lights fibre optics basics

  1. Red

  2. Violet

  3. Indigo

  4. Yellow

Show answer
Correct Option: B
Explanation:

Violet is having shortest wavelength among VIBGYOR. 

We know,            $\nu\times \lambda=c$
   Frequency is a constant quantity.
also, 
                           $\mu=\dfrac{velocity\ of\ light\ in\ vacuum}{velocity\ of\ light\ in\ a\ medium}$
  so, refractive index property for violet will be maximum and it will refract the most.

Which of the following colour of light undergoes the maximum deviation while passing a glass prism ?

physics spectra sunlight - white and coloured sunlight - combination of 7 lights fibre optics basics

  1. Red

  2. Blue

  3. Violet

  4. Green

Show answer
Correct Option: C
Explanation:

Violet undergoes maximum deviation while passing through a prism because it has least wavelength , as we know,

            We know,            $\nu\times \lambda=c$
   Frequency is a constant quantity.
also, 
                           $\mu=\dfrac{velocity\ of\ light\ in\ vacuum}{velocity\ of\ light\ in\ a\ medium}$
  so, refractive index property for violet will be maximum and it will refract the most. and will have the greatest deviation.

When light passes through a medium that consists of scatters such as water vapour, dust particles, which colour of light experiences highest scattering?

physics spectra sunlight - white and coloured sunlight - combination of 7 lights fibre optics basics

  1. $Violet$

  2. $Red$

  3. $Yellow$

  4. $Orange$

Show answer
Correct Option: A
Explanation:

Violet have least wavelength among the visible light spectra.

       According to Rayleigh Criterion,  Scattering probability is proportional to $\dfrac{1}{\lambda^4}$.
So, violet light will be scattered the most.

When light enters a dispersive medium, light wave of different wavelength travels with different velocities.

physics spectra sunlight - white and coloured sunlight - combination of 7 lights fibre optics basics

  1. Yes

  2. No

  3. Sometimes

  4. When medium is a fibre

Show answer
Correct Option: A
Explanation:

Yes, speed becomes different for different wavelengths in a particular medium. In a given dispersive medium the speed for different colours is different and due to this phenomenon we can see the spectrum of VIBGYOR.

Assertion: Different colours travel with different speed in vacuum.
Reason : Wavelength of light depends on refractive index of medium.

physics spectra sunlight - white and coloured sunlight - combination of 7 lights fibre optics basics

  1. Both assertion and reason are true but the reason is the correct explanation of assertion

  2. Both assertion and reason are true but the reason is not the correct explanation of assertion

  3. Assertion is true but reason is false

  4. Both the assertion and reason are false

  5. Reason is true but assertion is false

Show answer
Correct Option: E
Explanation:

In vacuum all the colours have same velocity but their velocity changes when they enter in a medium. In the medium their velocity changes due to change in their wavelength.
$v=n\lambda $
If $\lambda $ changes, v also changes for a particular colour therefore, different colours have different wavelength ($\lambda $).

What is known as dispersion of light?

physics spectra sunlight - white and coloured sunlight - combination of 7 lights fibre optics basics

  1. The phenomenon due to which a polychromatic light, like sunlight, splits into its component colours, when passed through a transparent medium

  2. The phenomenon due to which a polychromatic light, like sunlight, splits into its component colours, when passed through a opaque medium

  3. The phenomenon due to which a polychromatic light, like sunlight, splits into its component colours, when passed through a translucent medium

  4. The phenomenon due to which a polychromatic light, like sunlight, do not splits into its component colours, when passed through a transparent medium

Show answer
Correct Option: A
Explanation:

When white light pass through a glass prism the white light get scatter in so many colours of light according to it's frequency and the lights are (VIBGYOR) ,this phenomena of scattering of light is called
dispersion of light.

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Due to which property of colours they appear differently though the sunlight is passed through only one medium?

physics spectra sunlight - white and coloured sunlight - combination of 7 lights fibre optics basics

  1. Due to different refractive index with respect to medium

  2. Due to different frequencies with respect to medium

  3. Due to different amplitudes with respect to medium

  4. Due to different colour with respect to medium

Show answer
Correct Option: A
Explanation:

Refraction is a phenomenon that happens when a beam of white light passes through the interface between air and a denser medium, such as glass or water. Light travels more slowly in a denser medium, so it changes direction – or refracts – when it passes through the interface. White light is a mixture of all the wavelengths of light, and each wavelength refracts at a slightly different angle. Therefore, when the beam emerges from the denser medium, it has been split into its component wavelengths. The ones you can see form the familiar rainbow