Name: Total Internal Reflection From Prism
Uploaded: 2019-07-19
Duration: 1 min 56 s
Description: You must have seen reflectors on a bicycle. Why are they attached to the mudguards? What use do they have? Let’s watch this video on reflectors to find out.

Question

Explain with the help of neat ray diagrams the deviation of light through a prism by

(i) 90 °

,

(i i) 180 °

.

Accepted Answer

To deviate the path through $90 ° .$

Consider a right angled prsim $P Q R$ having refractive index value $1.5$ . Consider a ray $A B$ incident normally on the face $P Q$ . This ray will go undeviated and strikes the hypotenuse at an angle greater $(45 °)$ than critical angle. Since critical angle i.e $\sin i_{c} = \frac{1}{1.5} = 0.67 \Rightarrow i c \approx 42 °$ . The rays will be total internally reflected. By law of reflection angle $∠ i = ∠ r = 45 °$ . Hence, the light after total reflection from the surface $P R$ deviates $90 °$ from its path. SInce ray now strikes the face $Q R$ it will go undeviated.

To deviate the path through $180 ° .$

Consider a right angled triangle prism having refractive index $1.5$ . Therefore, the critical angle can be calculated in the same way as above i.e $i_{c} = 42 °$ . Now from the figure we can see a ray $A B$ is incident normally on to the prism face $P Q$ . The angle of incidence is $45 ° > i_{c}$ , therefore, ray will be total internally reflected, and again it will strike the face $Q R$ . Since, angle of incidence is greater than critical angle again it will be internally reflected through ray $D E$ it will come out of the face $P R$ undeviated. Hence, the ray that entered the face $P R$ comes out of the same face $P R$ thus deviating $180 °$ from its path.

Explain with the help of neat ray diagrams the deviation of light through a prism by $(i) 90 °$ , $(i i) 180 °$ .

Important Questions on Refraction at Plane Surfaces

Learn and Prepare for any exam you want !

Explain with the help of neat ray diagrams the deviation of light through a prism by i 90°, ii 180°.

Important Questions on Refraction at Plane Surfaces

Learn and Prepare for any exam you want !

Explain with the help of neat ray diagrams the deviation of light through a prism by $(i) 90 °$ , $(i i) 180 °$ .