Explain the phenomenon of total internal reflection with one or two activities. (AS1)

When the angle of incidence is greater than the particular angle (called as critical angle) than the ray of light instead of refracting gets reflected into denser medium at the interface. This phenomenon is called as the total internal reflection.

Conditions Of Total internal Reflection: Total internal reflection takes place when both of the following two conditions are met:

• The light is in the denser medium and approaching the less dense medium.

• The angle of incidence is greater than the so-called critical angle.

Activity 1:

1. Place the semicircular disc in such a way that diameter coincides with the interface and centre coincides with the center of the interface.

2. Now send the light along the curved side of the disc and. Start with angle of incidence 0^o .

3. Send the laser along the angles 5^o, 10^o, 15^o,… and measure the angle of refraction.

Observation: We will observe that at certain angle of incidence the refracted ray does not come out but gazes the interface. This angle of incidence is called as the critical angle. Figure below depicts the same.