Tracing the path of the rays of light through a glass prism
To trace the path of the rays of light through glass prism.
- A drawing board
- Few drawing pins
- A glass prism
- Few sharp pointed alpins
- Three sheets of white paper
- A measuring scale
- A pencil
- A protractor
A prism is a portion of refracting medium bounded by the planes inclined to each other at an angle.
When a ray of light travels from a rarer medium towards denser medium, it bends towards the normal. if the ray of light goes from denser to rarer, it bends away from the normal.
- Fix a sheet of white paper on a drawing board.
- Place the prism on the paper and mark its boundary as shown in figure.
- Remove the prism and draw a normal at E on side AB.
- Draw a line PE making an angle 30° with the normal.
- Fix two pins at P and Q on the line PE about 6 cm apart from each other.
- Place the prism back to its position.
- Look through face AC for images of pins P and Q. Fix points R and S so that they appear in line with the images of pins P and Q.
- Remove the pins and join RS to give emergent ray.
- Measure angle of emergence and angle of deviation after removing prism and the pins.
- Repeat the above procedure for two more angles of incidence i.e., 45° and 60°.
Angle of prism = 60°
|S.No.||Angle of incidence (∠i)||Angle of emergence (∠e)||Angle of deviation (∠δ)|
*These values may be different for different prism.
i + e = A + δ
Error Reduction and Precautions
- The angle of incidence should be in between 30° and 60°.
- Use a sharp pencil to properly draw boundary of prism and rays of light.
- The alpins should have sharp tip and should be fixed vertically.
- The distance between the alpins should be atleast 6 cm for greater accuracy.
- The prism should be smooth, transparent and clean.
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