Refraction Of Light Class 10th Science Lab Manual CBSE Solution

Class 10th Science Lab Manual CBSE Solution

Lab Experiment 11
Question 1.

AIM

To trace the path of a ray of light passing through a rectangular glass slab for different angles of incidence. Measure the angle of incidence, the angle of refraction, the angle of emergence and interpret the result.


Answer:

MATERIALS REQUIRED


Drawing board, drawing pins, three plane sheets of white paper a rectangular glass slab, geometry instruments and pins.


THEORY

When a light ray incident on air to glass interface through a glass slab obliquely has the following characteristics:
1. When a light ray travels from air to glass, the ray bends towards the normal at the surface of the air-glass boundary.

2. When a light ray travels from glass to air, the angle of refraction is greater than the angle of incidence of glass-air interfaces as the ray of light bends away from the normal


3. If the angle of incidence is zero, i.e. the incident ray is normal to the interface, the ray of light continues to travel in the same direction after refraction. 
4. The angle of emergence and the angle of incidence will be equal. 

PROCEDURE


1. Fix a white paper sheet on a drawing board using pins or cello tape.


2. Place a rectangular glass slab in the middle of the paper part and marks its boundary ABCD with a pencil.


3. Remove the rectangular glass slab and label the boundary as A1, B1, C1, D1 as shown below.


4. Draw normal (perpendicular) MN on the side AB at a point O, slightly away from the centre towards A1.


5. Draw an oblique line P1, Q1 (incident ray) such that ∠P1Q1M = 30 (Angle of incidence). Fix two sharp point pin P1 and Q1 vertically erected on the line P1Q1 at a distance of 5-7 cm apart.


6. Place the glass slab again within the marked position. Observe the image of Look of pins (not their heads) P1 and Q1 from the other side. Fix other two pins R1 and S1 in such a way that R1, S1, and the image of P1, and Q1 lie on a straight line.


7. Now, remove the glass slab and pins. Mark all the prick of the pins. Join the points R1 and S1 and produce a line upto the edge C1D1. Let R1S1 meet C1D1 at O2. This will act as an emergent ray.


8. Draw a normal M1, N1, at O1. Join O1 and O. It will represent the path of ray inside the glass slab, i.e. refracted ray.


9. Measure the angle of emergence, i.e. ∠e = ∠N1O2S1 and angle of refraction, i.e. ∠r = N1O1O2.


10. Repeat the experiment for two more values of angles of incidence such as 45 and 60 on the other part of the paper and measure the angle of refraction and emergence accordingly and tabulate them.



OBSERVATION TABLE



RESULT


1. law of refraction is verified, i.e. at the point of incidence the incident ray, the emergent ray and the normal to the air-glass interface, all lie in the plane of the paper.


2. The relation between the angle of incidence and the angle of emergence are obtained within the experimental limits.


3. From the observation, the emergent ray emerging out of the rectangular glass slab is parallel to the incident ray.


4. Emergent ray undergoes lateral displacement.



5. The angle of refraction increases with increase in the angle of incidence.


PRECAUTIONS


1. The glass slab should be perfectly rectangular with all its faces smooth.


2. Glass slab must be clean and free from scratches.


3. Thin lines should be drawn to obtain good accuracy.


4. The distance between the pins should be 5-7 cm.


5. The base of all the pins should be placed in a straight line.



Viva Questions
Question 1.

What is refraction ?


Answer:

When a beam of light falls obliquely at the interface of the two optical media, the direction of its paths changes when it enters into the other medium.This phenomenon is called refraction.



Question 2.

During refraction what happens to speed , wavelength and frequency of the wave?


Answer:

The speed and wavelength of the light changes while frequency remains the same.



Question 3.

When travelling from a rarer medium to denser medium , the ray will bend on which reaction ?


Answer:

The ray of light bends toward the normal.



Question 4.

When a ray of light travels from a denser medium to rarer, where the light will move in respect to normal?


Answer:

the light will bend away from the normal.



Question 5.

What are the laws of refraction?


Answer:

1. At the point of incidence the incident ray ,normal ray and the refracted ray lie on the same plane.


2. The ratio of the sine of an angle to the sine of the angle of refraction is constant for the medium for the same colour of light.



Question 6.

What is Snell's law?


Answer:

The refractive index of the medium is equal to the ratio of the sine of the angle of incidence and sine of the angle of refraction.



Question 7.

What factors does the refractive index of a medium depend?


Answer:

1. Density of medium


2. Nature of medium



Question 8.

What is the unit of the refractive index?


Answer:

The refractive index is a dimensionless quantity since it is the ratio of two like quantities.



Question 9.

What happen to the emergent angle on increasing the incident angle at the air-glass interface?


Answer:

Angle of emergence also increases.



Question 10.

What is lateral displacement?


Answer:

The lateral Displacement is the perpendicular distance between the incident ray and emergent ray.



Question 11.

State the condition when no refraction occurs?


Answer:

1. The light rays fall along the normal


2. The refractive index of two optical media are equal



Question 12.

Why do you measure the perpendicular distance?


Answer:

Because incident ray and emergent ray both are parallel to each other.



Question 13.

Why should the pins be fixed at least 4 to 6 cm apart?


Answer:

1. To get more light


2. It will be more convenient to fix other pins.



Question 14.

How does the reflection of light different from refraction?


Answer:

In reflection, a ray of light turns back into the same medium after reflection, while in refraction the ray of light passes from one medium to another.


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