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# how do you find experimentally the refractive index of material of a prism

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## How do you find experimentally the refractive index of material of a prism.

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AIM: To determine refractive index of the material of the given prism by the method of i-d curve.

Materials required: Prism, piece of white chart of size 20 x 20 cm, pencil, pins, scale and protractor.

PROCEDURE:

Take a prism and place it on the white chart in such a way that the triangular base of the prism is on the chart.

Draw a line around the prism using a pencil. Remove the prism.

It is a triangle. Name its vertices P, Q and R.

Find the angle between PQ and PR. This is the angle of the prism (A).

Mark M on the side of triangle PQ and also draw a perpendicular to the PQ at M.

Place the centre of the protractor at M and along the normal mark an angle of 30° and then draw line up to M.

This angle is angle of incidence and note it in a table.

Place the prism in its position again.

Now fix two pins vertically on the line at point A and B.

Look for the images of pins through the prism from the other side and fix another two pins at points C and D in such a way that all the four pins appear to lie along same straight line.

Now remove the prism and take out pins.

Draw a line joining the two pin-holes formed by the pins to meet surface PR.

The angle between the normal at N and the emergent ray is the angle of emergence.

Join M and N. A,B,M,N, C, D represent the path of light.

Extend both incident, emergent rays tell they meet at a point ‘O’.

The angle between these two rays is angle of deviation denoted by ‘D’.

Do the same for various angles of incidence such as 40°, 50° etc.

If we take angle of incidence along x-axis and the angle of deviation along y-axis we get the graph as shown in figure.

The refractive index of prism μ=

sin 2 A ​ sin[ 2 (A+D) ​ ] ​

RESULT: Refractive index of the material of the prism

259 27

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## How do you find experimentally the refractive index of material of a prism ?

Aim: To find the refractive index of a prism. Material required : Prism, piece of white chart of size 20xx20 cm, pencil, pins, scale and protector. Procedure : 1) Take a prism and place it on the white chart in such a way that the triangular base of the prism is on the chart. 2) Draw a line around the prism base using pencil. Remove the prism and name the vertices of the triangle as formed as P, Q and R. 3) Measure the angle between PQ and PR. This is the angle of the prism (A). 4) Mark M on the side of DeltaPQR and also draw a perpendicular to PQ at M. 5) Draw a line with 30^(@) to the normal at M. This line denotes the incident ray. Note the value in the table. 6) Place the prism in its position (Delta) again. 7) Now fix two pins vertically on the line at the points A and B. 8) Look for the angles of pins through the prism from the other side (PR) and fix another two pins at points C and D in such a way that all the four pins appear to lie along the same straight line. 9) Now remove the prism and take out pins. 10) Draw a line joining C and D and extend it to meet PR at N. This is the emerging ray. 11) Draw a normal to PR at N . 12) The angle between the normal at N and emergent ray is the angle of emergence . Measure this angle and note its value in the above table. 13) Now join the points M and N by a straight line. The line passing through A,B,M,N,C and D represents the path of light when it suffers refraction through the prism. 14) Extend both incident and emergent rays till they meet at point 'O'. 15) Measure angleMON. This is the angle of deviation, denoted by 'd'. Note this value in the table. 16) Repeat the process for different angles of incidence and measure corresponding angles of deviations. 17) Take angle of incidence along X-axis and the angle of deviation along y-axis . Draw a graph. 18) We obtain a curve. 19) Draw a tangent line to the curve, parallel to X-axis , at the lowest point of the graph. The point where this line cuts Y-axis gives the angle of minimum deviation (D). (20) The refractive index of prism n= (sin((A+D)/(2)))/(sin((A)/(2))) (21) Using this formula , we can measure the refractive index of the material of the prism.

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How do you find experimentally the refractive index of material of a prism ?

Text Solution Open Answer in App Solution

Aim: To find the refractive index of a prism.

Material required : Prism, piece of white chart of size

20×20 20×20

cm, pencil, pins, scale and protector.

Procedure :

1) Take a prism and place it on the white chart in such a way that the triangular base of the prism is on the chart.

2) Draw a line around the prism base using pencil. Remove the prism and name the vertices of the triangle as formed as P, Q and R.

3) Measure the angle between PQ and PR. This is the angle of the prism (A).

4) Mark M on the side of

ΔPQR ΔPQR

and also draw a perpendicular to PQ at M.

5) Draw a line with 30 ∘ 30∘

to the normal at M. This line denotes the incident ray. Note the value in the table.

6) Place the prism in its position (

Δ Δ ) again.

7) Now fix two pins vertically on the line at the points A and B.

8) Look for the angles of pins through the prism from the other side (PR) and fix another two pins at points C and D in such a way that all the four pins appear to lie along the same straight line.

9) Now remove the prism and take out pins.

10) Draw a line joining C and D and extend it to meet PR at N. This is the emerging ray.

11) Draw a normal to PR at N .

12) The angle between the normal at N and emergent ray is the angle of emergence . Measure this angle and note its value in the above table.

13) Now join the points M and N by a straight line. The line passing through A,B,M,N,C and D represents the path of light when it suffers refraction through the prism.

14) Extend both incident and emergent rays till they meet at point 'O'.

15) Measure ∠MON ∠MON

. This is the angle of deviation, denoted by 'd'. Note this value in the table.

16) Repeat the process for different angles of incidence and measure corresponding angles of deviations.

17) Take angle of incidence along X-axis and the angle of deviation along y-axis . Draw a graph.

18) We obtain a curve.

19) Draw a tangent line to the curve, parallel to X-axis , at the lowest point of the graph. The point where this line cuts Y-axis gives the angle of minimum deviation (D).

(20) The refractive index of prism n=

sin( A+D 2 ) sin( A 2 ) sin(A+D2)sin(A2)

(21) Using this formula , we can measure the refractive index of the material of the prism.

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## How do you find experimentally the refractive index of material of a prism?

How do you find experimentally the refractive index of material of a prism?. Ans: Hint : We need to construct a table with various values of angle of incidence of light falling on a prism and angle of deviation determined. Then the refractive index ...

## How do you find experimentally the refractive index of material of a prism?

Answer Verified 177.9k+ views 3 likes

Hint : We need to construct a table with various values of angle of incidence of light falling on a prism and angle of deviation determined. Then the refractive index formula using angle of prism and deviation is used to find the refractive index of the material of the prism.

Formula Used: The formulae used in the solution are given here.

⇒η = sin[ (A+D) 2 ] / sin A 2

⇒η = sin⁡[(A+D)2] /sin⁡[(A+D)2]sin⁡A2 sin⁡A2

where η η

is the refractive index of the prism,

A A

is the angle of prism and

d d is the deviation.

The experiment can be explained as below,

Aim: Finding the refractive index of the prism.

Material required: Prism, piece of white chart paper, pencil, pins, scale and protractor.

Procedure:

1. A prism is placed on the white chart with the triangular base on the chart. The base is traced before removing the prism.

2. The vertices of this triangle are named P, Q and R, as shown in the figure. The angle of the prism,

∠QPR=A ∠QPR=A .

3. At a point M on the side PQ, a line is drawn perpendicular to PQ.

4. At M, along the normal an angle of

30 ∘ 30∘

is marked. A line is then drawn up to M. This is the angle of incidence and its measure is noted.

5. The prism in its position again and two pins are fixed vertically on the line at point A and B.

6. The images of pins through the prism from the other side are found and two other pins are fixed at points C and D in such a way that all the four pins appear to lie along the same straight line.

7. The prism is removed. A line joining the two pin-holes formed by the pins to meet surface PR.

8. The angle between the normal at N and the emergent ray is the angle of emergence.

9. M and N are joined. A, B, M, N, C, D represents the path of light.

10. Both the incident and emergent rays meet at a point ‘O’. The angle between these two rays is the angle of deviation.

11. The same process is repeated for various angles of incidence such as

40 ∘ 40∘ , 50 ∘ 50∘ etc.

12. Taking angle of incidence along

x x

-axis and the angle of deviation along

y y

-axis we get the graph as shown in figure.

13. The refractive index of prism is given by the formula,

⇒η = sin[ (A+D) 2 ] / sin A 2

⇒η = sin⁡[(A+D)2] /sin⁡[(A+D)2]sin⁡A2 sin⁡A2

where η η

is the refractive index of the prism,

A A

is the angle of prism and

d d is the deviation.

Using this formula, the refractive index of the material of the prism can be measured.

Note

A spectrometer can also be used to find the refractive index of a prism. It uses Snell’s law to find the refractive index. Prism is used to get a spectrum of light. Refraction takes place in prism.

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