# Dispersion of Light by Prism Class-8th Goyal Brothers ICSE Physics Solution Chapter-5 Unit-4

Dispersion of Light by Prism Class-8th Goyal Brothers ICSE Physics Solution Chapter-5 Unit-4 (Dispersion of Light by a Prism). We Provide Step by Step Answers of Objective, True False, Incorrect and Correct, Fill in the blanks, Match the following , Short/Long Answer Type of Chapter-5 (Light Energy), unit-4 (Dispersion of Light by a Prism) Visit official Website  for detail information about ICSE Board Class-8.

## Dispersion of Light by Prism Class-8th Goyal Brothers ICSE Physics Solution Chapter-5 Unit-4

 Board ICSE Class 8th Subject Physics Book Name Goyal Brothers Chapter-5 Light Energy Unit-4 Dispersion of Light by a Prism Topic Solution of exercise questions Session 2023-24

### OBJECTIVE QUESTION

Dispersion of Light by a Prism Class-8th Goyal Brothers ICSE Physics Solution Chapter-5 Unit-4

#### Que: A. Fill in the blank spaces by choosing the correct words from the list given below :

List : two, base, dispersion, prism, deviation

1. When the refraction takes place through a glass prism the emergent ray always bends towards the base of prism.

2. The phenomenon due to which white light splits up into seven colours, on passing through an equilateral prism is called dispersion of light.

3. A prism is a piece of transparent material having three rectangular surfaces and two triangular surfaces.

4. The angle between the incident ray and emergent ray, when the ray is passing through an equilateral prism is called angle of deviation.

5. The angle between the two refracting surface of a prism is called angle of prism.

#### Que: B. Statements given below are incorrect. Write the correct statements :

##### Question: 1. A prism is a piece of transparent material having three triangular and two rectangular surfaces.

Answer: A prism is a piece of transparent material having two triangular and three rectangular surfaces.

##### Question: 2. For an equilateral prism ∠A + ∠i = ∠e + ∠D.

Answer: For an equilateral prism ∠i + ∠e = ∠A + ∠D.

##### Question: 3. The angle between the incident ray and the refracted ray of a prism is called angle of deviation.

Answer: The angle between the incident ray and the emergent ray of a prism is called angle of deviation.

##### Question: 4. The phenomenon due to which white light splits into seven colours on passing through a prism is called spectrum.

Answer: The phenomenon due to which white light splits into seven colours on passing through a prism is called dispersion.

##### Question: 5. During dispersion of white light by a prism, the red colour deviates most.

Answer: During dispersion of white light by a prism, the violet colour deviates most.

#### Que: C. Write ‘True’ or ‘False’ for the following statements :

 Statements True/False 1. The band of seven colours obtained on a screen when white light passes through a prism is called spectrum. T 2. It is first face of a prism which disperses white light. T 3. During refraction through prism a ray bends away from its base. F 4. For a prism ∠A + ∠D = ∠i + ∠e. T 5. The phenomenon due to which white light splits into seven colours on passing through the prism. F

#### Que: D. Tick (√) the most appropriate answer :

##### 1. When the white light is passed through an equilateral prism it splits into seven colours. The phenomena of splitting of white light is called :

(a) refraction

(b) spectrum

(c) dispersion

(d) none of these

Answer: option (c) dispersion is correct.

##### 2. During dispersion of light, the least dispersed colour is :

(a) violet

(b) green

(c) yellow

(d) red

Answer: option (d) red is correct.

##### 3. When the refraction takes place through an equilateral prism:

(a) ∠A + ∠i = ∠D + ∠e

(b) ∠A + ∠e = ∠D + ∠i

(c) ∠A + ∠D = ∠i + ∠e

(d) none of these

Answer: option (c) ∠A + ∠D = ∠i + ∠e is correct.

##### 4. The angle between two refracting surfaces of a prism is called :

(a) angle of prism

(b) angle of deviation

(c) angle of refraction

(d) none of these

Answer: option (a) angle of prism is correct.

##### 5. The band of seven colours formed, when the white light splits on passing through a prism is called :

(a) dispersion

(b) refraction

(c) spectrum

(d) refractive index

Answer: option (c) spectrum is correct.

#### Que: E. Match the statements in Column A, with those in Column B :

 Column A Column B 1. A transparent piece of glass used for the dispersion of white light. (a) Angle of prism 2. The angle between incident ray and emergent ray, when refraction takes place through a prism. (b) Spectrum 3. The angle between two refracting surfaces of a prism. (c) Dispersion 4. A band of colours formed on the screen when white light passes through prism. (d) Prism 5. The phenomenon due to which white light splits into seven colours on passing through the prism. (e) Angle of deviation

 Column A Column B 1. A transparent piece of glass used for the dispersion of white light. (a) Prism 2. The angle between incident ray and emergent ray, when refraction takes place through a prism. (b) Angle of deviation 3. The angle between two refracting surfaces of a prism. (c) Angle of prism 4. A band of colours formed on the screen when white light passes through prism. (d) Spectrum 5. The phenomenon due to which white light splits into seven colours on passing through the prism. (e) Dispersion

### STUDY QUESTION

Dispersion of Light by a Prism Class-8th Goyal Brothers ICSE Physics Solution Chapter-5 Unit-4

#### Question: 2. (a) Define the following when refraction takes place through an equilateral glass prism (i) angle of incidence (ii) prism (iii) refracting angle of prism (iv) angle of emergence (v) angle of deviation.

Answer: Ray of light passes through an equilateral glass prism such that the angle of incidence is equal to the angle of emergence and each of these angles is equal to 3/4 of angle of prism. Angle of deviation for a ray of light in a prism is given by, Prism is an equilateral triangle.

#### (b) How are angle of incidence, angle of prism, angle of emergence and angle of deviation related to each other?

Answer: When a ray of light suffers minimum deviation through prism, angle of incidence is equal to the angle of emergence. Ray of light passing through the prism will be parallel to the base of the prism. Angle of refraction inside the material of the prism is half the angle of the prism.

#### (i) Spectrum

Answer: A spectrum is a condition that is not limited to a specific set of values but can vary, without gaps, across a continuum. The word was first used scientifically in optics to describe the rainbow of colors in visible light after passing through a prism.

#### (ii) Dispersion

Answer: Visible light is actually made up of different colors. Each color bends by a different amount when refracted by glass. That’s why visible light is split, or dispersed, into different colors when it passes through a lens or prism. This process of splitting of white light into seven colours is called dispersion of light.

#### (b) Why does the white light split on the first refracting face of prism ?

Answer: When a white light ray falls on the first surface of a prism, light rays of different colours due to their different speeds in glass get refracted (or deviated) through different angles. Thus, the dispersion of white light into its constituent colours takes place at the first surface of prism.

#### Question: 5. Write all the colours of spectrum in proper order, starting from red colour.

Answer: The colors of the visible spectrum include red, orange, yellow, green, blue, indigo, and violet. The acronym ROYGBIV may be helpful in remembering the order of the colors that make up the visible spectrum.

#### (a) deviates least

Answer: When white light falls on a glass prism, each colour in it is refracted by a different angle, from which red colour is least deviated and violet most.

#### (b) deviates most

Answer: Among the 7 constituent colours of light, violet light has the least wavelength and hence it deviates the most and red light having the largest wavelength deviates the least.

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