Question

Explain the refraction of light through a triangular glass prism using a labeled ray diagram. Hence define the angle of deviation.

Answer 1

Step 1: Refraction

1. Refraction is the phenomenon in which when light travels from one medium to another, it changes its speed and hence its path of propagation.
2. The amount of refraction can be estimated using the refractive index of the given medium.
3. If $c$ is the speed of light in vacuum and $v$ is the speed of light in a given medium, then the refractive index of this medium is $\mu =\frac{c}{v}$.

Step 2: Refraction through a Prism:

The given figure shows the passage of light through a triangular prism $ABC$.

The angle of incidence and refraction at the first face $AB$ are $i$ and $r_1$, while the angle of incidence (from glass to air) at the second face $AC$ is $r_2$ and the angle of refraction or emergence $e$.

Step 3: Angle of Deviation

The angle between the emergent ray and the direction of the incident ray is called the angle of deviation, $\delta$.

The formula for angle of deviation is given as,

$\delta =i+e-A$

where, $A$ is the angle of the prism as shown in the figure.