Tag: light and the formation of shadows

Questions Related to light and the formation of shadows

It was the British scientist _______who discovered in 1666 that light consists of seven colours. Fill in the blank.

newton's colour disc light and the formation of shadows physics

  1. Henry

  2. John Dalton

  3. Sir Issac Newton

  4. Einstein

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Correct Option: C
Explanation:

Correct answer is (a) Sir Issac Newton.

In 1666, during one of his optical experiments, Newton passed a beam of sunlight through a glass prism. The glass prism split the light into a band of seven colours on his wall. This phenomena is known as dispersion of light

He called this band of colours the ‘spectrum’. Thus the spectrum is a band of seven colours which is obtained by splitting of white light by a glass prism.

The discovery of Newton's colour disc proves which of the following statement?

newton's colour disc light and the formation of shadows physics

  1. Light is colourless

  2. Light is not colourless

  3. Light has only 1 colour

  4. Light has only 3 basic colours

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Correct Option: B
Explanation:

The perception of a picture or a color stays in the human brain for a fraction of a second. Newton's color disk is a mechanical device that rotates an array of colors arranged as petals or gradients around an axis and when the disc rotates fast enough the perception of the color changes to white. This is because white light is nothing but the mixture of light of all wavelengths in the visible range.

Sir Isaac Newton used this device to prove the above assertion that white color is the mixture of all colors.

SO Light is not colourless.

When sun rays are passed through a glass prism it gets

newton's colour disc light and the formation of shadows physics

  1. Deviated, but not dispersed

  2. Deviated and dispersed

  3. Dispersed, but not deviated

  4. Neither deviated nor dispersed

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Correct Option: B

Which of the following two colours are complementary colours? 

newton's colour disc light and the formation of shadows physics

  1. Red and Gresn

  2. Red and Magenta

  3. Red and Cyan

  4. Yellow and Red

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Correct Option: C

When a drop of water is introduced between the glass plate and plano-convex lens in Newton's rings system, the ring system

newton's colour disc light and the formation of shadows physics

  1. Contracts

  2. Expands

  3. Remains same

  4. First expands then contracts

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Correct Option: A
Explanation:

The diameter of Newton's rings is inversely proportional to refractive index. Therefore when a drop of water is introduced between the glass plate and plano-convex lens in Newton's rings, the ring system contacts. 

Rainbow is observed when the Sun is 

newton's colour disc light and the formation of shadows physics

  1. In front of the observer

  2. Behind the observer

  3. Vertically above the observer

  4. In any of these position

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Correct Option: B
Explanation:

The sun is always behind the observer. This is because the rainbow is actually just sunlight which has been refracted and reflected.

In the Newton's rings set up, when a drop of water is introduced between the glass plate and planoconvex lens the observed ring system

newton's colour disc light and the formation of shadows physics

  1. Contracts

  2. Expands

  3. Remains the same

  4. Expands and then contracts

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Correct Option: A
Explanation:

Since diameter of the ring is inversely proportional to the square root of refractive index of the medium between the planoconvex lens and plane glass plate, therefore as refractive index increases, diameter of the rings decrease, that is the rings contract. 

In Newton's experiment the radii of the $m^{th}$ and $(m+4)^{th}$ dark rings are respectively $\sqrt{5}$mm and $\sqrt{7}$mm. What is the value of m?

newton's colour disc light and the formation of shadows physics

  1. $2$

  2. $4$

  3. $8$

  4. $10$

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Correct Option: D
Explanation:

Radius of mth dark fringe   $r _m = \sqrt{mR\lambda}$
Thus we get  $r _{m+4} = \sqrt{7} = \sqrt{(m+4)R\lambda}$     ......(1)
Also,  $r _m = \sqrt{5} = \sqrt{mR\lambda}$      .......(2)
Dividing equation (1) with equation (2),  
$ \sqrt{\dfrac {m+4}{m} }= \sqrt{\dfrac{7}{5}}$
$\dfrac{m+4}{m} = \dfrac{7}{5}$
$5(m+4)= 7m$
$5m+20= 7m$
$2m=20$
$\implies   \ m=10$