State the Cause of Dispersion of White Light Passing Through a Glass Prism. How Did Newton Show that White Light of Sun Contains Seven Colours Using Two Identical Glass Prisms. - Science


State the cause of dispersion of white light passing through a glass prism. How did Newton show that white light of sun contains seven colours using two identical glass prisms. Draw a ray diagram to show the path of light when two identical glass prisms are arranged together in inverted position with respect to each other and a narrow beam of white light is allowed to fall obliquely on one of the focus of the first prism.



Different colours of light bend through different angles with respect to the incident ray as they pass through a prism. The red light bends the least, while the violet bends the most. Thus, the rays of each colour emerge along different paths and thus become distinct. This is the cause of dispersion of white light passing through a glass prism.

Isaac Newton used two glass prims, with one prism in inverted position to show that white light of the Sun contains seven colours. The set-up has been shown below:-

When white light of the Sun passes through the first prism, it gets dispersed into seven colours. When all the seven colours of the spectrum were passed through the second prism, Newton found a beam of white light emerging from the other side of the second prism. This observation gave Newton the idea that the sunlight is made up of seven colours.

Concept: Dispersion of Light Through Prism and Formation of Spectrum
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2015-2016 (March) Delhi Set 3


A student is observing a diagram showing the path of a ray of light passing through a glass prism. He would find that for all angles of incidence the ray of light bends:

Draw a ray diagram to explain the term angle of deviation.

In the following diagram the correctly marked angles are : 

(a) ∠A and ∠e

(b) ∠i, ∠A and ∠D

(c) ∠A ∠r and ∠e

(b) ∠A ∠r and ∠D

Study the following ray diagram:

In this diagram, the angle of incidence, the angle of emergence and the angle of deviation respectively have been represented by

(A) y, p, z

(B) x, q, z

(C) p, y, z

(D) p, z, y

When a beam of white light is passed through a prism, it splits to form lights of seven colours. Is it possible to recombine the lights of seven colours to obtain the white light again? Explain your answer.

Which is refracted most by a prism : red light or violet light? Explain why?

The colour of white light which is deviated the maximum on passing through the glass prism is:
(a) blue
(b) indigo
(c) red
(d) orange

The splitting up of white light into seven colours on passing through a glass prism is called:
(a) refraction
(b) deflection
(c) dispersion
(d) scattering

The coloured light having the maximum speed in glass prism is:
(a) blue
(b) green
(c) violet
(d) yellow

Which of the following colour of white light has the least wavelength?
(a) red
(b) orange
(c) violet
(d) blue

The splitting of white light into its constituent colours is called .............

The speed of light in air or vacuum is

A ray of light moving from an optically rarer to a denser medium

The seven colours in the spectrum of sunlight in order, are represented as :

State the speed of light in (a) air, (b) water, and (c) glass

Which is optically denser: water or air? Give reason

Out of air and glass, which is optically rarer? Give reason.

In figure AO is the ray of white light falling on a prism PQR. Complete the diagram till the light emerges out from the prism and falls on the screen.

What do you understand by the term spectrum? Name the various colours present in the spectrum of sunlight.

You are given a disc divided into seven sectors with colours violet, indigo, blue, green, yellow, orange and red in them. What would be its colour when it is rotated rapidly?

A rock salt prism is used instead of a glass prism to obtain the infrared spectrum.

What do you understand by the term spectrum?

Complete the ray diagram given below to show the nature of light produced on the screen.

The completed ray diagram is as shown below : 

What is a spectrum? Draw a labeled ray diagram to show the formation of spectrum of white light.

An object AB is placed in front of a convex lens as shown in fig. 4. Complete the ray diagram and obtain the image formed and state the nature of the image.

Name the material prism required for obtaining the spectrum of infra red radiation.

The phenomenon of splitting of light into its component colours is ___________ .

Draw a labelled diagram: Dispersion of light through a prism.

Answer the following:

What do you mean by dispersion? Name the different colours of light in the proper sequence in the spectrum of light. 

Which characteristic property of light is responsible for the blue colour of the sky?

How can the presence of ultraviolet radiation be detected?

Suggest one way, in each case, by which we can detect the presence of Infrared radiations.

In the figure, a beam of light consisting of three colours blue, red, and yellow is incident on a prism and on a rectangular glass block respectively. Complete the diagram by drawings of the refracted and emergent rays.

Match the Columns:

Column ‘A’ Column ‘B’
The wavelength of red light (a) 600 nm
(b) 700 nm
(c) 500 nm

The process of separation of light into its component colours while passing through a medium is called _______.

Write an Explanation.

Critical angle

Draw a neat and labelled diagram for dispersion of light.

Rainbow is a beautiful natural phenomenon. It is the combined effect of a natural three processes together produced by light. Write it into the circle.

Observe the given figure and write appropriate phenomenon of light in the box.

The splitting of white light in to seven colors is called ______.

The sunlight can be split into its constituent colors using ______.


Rainbow is formed by dispersion of which light by water drops


After passing through a prism, white light splits into a band of seven colours

What is dispersion? Explain in detail.

Define dispersion of light.

State the correct sequence (1-7) of colours in the spectrum formed by the prisms A and B, shown in Figure 15.2.

Which one of the following is involved for the formation of rainbow in the sky? 

What is Newton’s disc?

In dispersion, the color of light that will bend more is ______.

The periscope is an optical device with a polished surface that reflects the light falling on it.

Curved mirrors have surfaces that are spherical, cylindrical, parabolic, and ellipsoid.

Assertion: We can see the rainbow in the sky when the rain starts falling after a spell of bright sunlight.
Reason: The rainbow is formed due to the dispersion of light.

What is a rainbow?

During dispersion of white light by prism placed in air, for a particular value of angle of prism,

______ colour is deviated the least in the spectrum of white light obtained with a glass prism.

The angle of deviation through a prism is minimum when

  1. Incident rays and emergent rays are symmetric to the prism.
  2. The refracted ray inside the prism becomes parallel to its base.
  3. The angle of incidence is equal to that of the angle of emergence.
  4. When the angle of emergence has doubled the angle of incidence.

Choose the correct answer from the options given below:

The dispersive powers of flint glass and crown glass are 0.053 and 0.034, respectively and their mean refractive indices are 1.68 and 1.53 for white light. Calculate the angle of the flint glass prism required to form an achromatic combination with a crown glass prism of refracting angle 4°:

dispersive power of crown glass? Given that µv = 1.5230, µr = 1.5145

A prism of refractive index `sqrt2` and refracting angle A produces minimum deviation δm of a ray on one face at an angle of incidence 45°, The values of A and δm are, respectively ______.

State True or False:

"Wavelength of red light is close to 700 nm.”

Observe the given diagram and answer the questions.

  1. Name the process shown in the figure.
  2. Name the colour that deviates the most.
  3. Name the colour that deviates the least.
  4. Name any one phenomenon in nature which is based on the above process.
  5. Define ‘spectrum’.


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