CBSE Class 10 Practicals Science Tracing the path of a ray of light passing through a rectangular glass slab for different angles of incidence. Measure the angle of incidence, angle of refraction, angle of emergence and interpret the result
Tracing the path of a ray of light passing through a rectangular glass slab for different angles of incidence. Measure the angle of incidence, angle of refraction, angle of emergence and interpret the result
Experiment: To trace the path of ray of light passing through a rectangular glass slab for different angles of incidence.
Hello students we have learnt that when a ray of light passes from one transparent medium to another transparent medium it changes the direction, this phenomena is known as refraction of light.
Objective of the experiment….
To study the refraction of light through glass slab and to measure the angle of incidence, angle of refraction, and angle of emergence.
Instruments required for the experiment…..
Wooden drawing board, plain paper and pin, glass slab, pencil, scale, protractor etc.
Assumptions used for the experiment…..
When a ray of light is allowed to strike obliquely on a glass slab of thickness ‘t’ suffers refraction twice; once from rarer medium to denser medium, and then again from denser medium to rarer medium and finally emerges out the glass slab. It is observed that the incident ray and emergent ray remain parallel to each other, as well as the angle of incidence is equal to angle of emergence i.e. i = e
Ray diagram showing the experimental condition……
Procedure to study the path of refracted and emergent ray….
1.) Take a permanent marker and mark a small point at the corner of the glass slab so that the marked side of glass should be easily visible.
2.) Take plain paper and fix it on wooden drawing board with the help of thumb pin.
3.) Now place a glass slab at the middle of board such that the marked side appear at the top and towards you (see the ray diagram).
4.) Draw the sharp outline of glass slab, remove glass slab and complete the quadrilateral ABCD as shown in fig.
5.) Using protractor draw normal through point P on side AB.
6.) Place protractor again n side AB aligned with normal and measure angle of 600 from side AB, so that the angle of incidence for ray EF should be 300.
∴ ∠ EPN = i,angle of incidence.
7.) Now fix two pins exactly vertical at points E and F. So that ray EF will be our incidence ray.
8.) Place the glass slab again on wooden board. Looking through face CD try to find the pins fixed at points E and F.
9.) Take one more pin in hand and fix them such that the pins at points E and F and the pin in your hand appears collinear to each other. Mark this point as J. Now take one more pin fix it on board such that the pins at point E, F, J and 4th one appear in straight line again. Mark this point as K.
10.) Remove the glass slab and mark positions of pins carefully. Now remove pins also and join the through point J and K up to side CD at point Q. So that the ray JK is emergent ray. Join PQ as refracted ray.
11.) Extend the paths of incident ray EF and emergent ray JK as shown in ray diagram.
12.) Measure angle of incidence (i), angle of refraction (r) and angle of emergence (e) and record in observation table.
13.) Repeat the above procedure for difference angles of incidence and complete the observation table.
Observation table…
Sr. No. | Angle of incidence
(i) |
Angle of refraction
(r) |
Angle of emergence
(e) |
1 | 300 | ||
2 | 400 | ||
3 | 500 | ||
4 | 600 | ||
5 | 700 |
Conclusions from the experiment…
- The extended paths of incident ray and emergent ray are always parallel to each other.
- The angle of incidence and angle of emergence are congruent.
Precautions that should be followed while performing experiment….
- Fix the pins exactly vertical to plane of wooden board.
- Do check the pins are collinear are not while tracing the path of refracted ray.
- Measure all the angles carefully.
Some important questions that needs to revised for the experiment…
Q.1) State the laws of refraction.
Answer:
The laws of refraction are given as below,
- Incident ray, refracted ray and normal lies in same plane at the point of incidence, and incident ray and refracted rays lies on opposite side of normal.
- For given pair of media, the ratio of sine of angle of incidence to the sine of angle of refraction is constant.
μ = sini/sinr
The constant is known as refractive index of the medium
Q.2) Explain the concept of refraction of light.
Answer:
Light ray has ability to penetrate through the transparent medium when it strikes on it. During this the ray gets bend slightly and changes its direction causes refraction of light.
The change in direction of light when it passes from one transparent medium to other is called refraction of light.
Along with direction, speed of light also gets changed when it travels from different media; this is also nothing but the refraction of light.