Q.3. Define the term angle of deviation.
Ans. When the ray of light suffers refraction at two inclined faces, The angle between the direction of incident ray and the emergent ray is called the angle of deviation and is denoted by greek alphabet delta.
Q.6.a. How does the angle of deviation produced by a prism change with increase in the angle of incidence. Draw a curve showing the variation in the angle of deviation with the angle of incidence at a prism surface.
Ans. As the angle of incidence increases, the angle of deviation decreases first and reaches to a minimum value ( δmin ) for a certain angle of incidence. By further increasing the angle of incidence, the angle of deviation is found to increase.
Q.6.b. Using the curve in part (a) above, how do you infer that for a given prism, the angle of minimum deviation δmin is unique for the given light.
Ans. For a given prism and given color of light, δmin is unique since only one horizontal line can be drawn parallel to i-axis at the lowest point of i-δ curve.
Q.8. How does the deviation produced by a prism depend on (i) the refraction index of its material, and (ii) the wave length of incident light.
Ans. (i) It is found that for a given angle of incidence, the prism with a higher refractive index produces a greater deviation than the prism which has a lower refractive index. A flint glass prism produces more deviation than a crown glass prism of same refracting angle.
(ii) The refractive index of a given transparent medium is different for the light of different colours. It decreases with the increase in the wavelength of light. Thus the refractive index of the material of a prism is maximum for the violet light and minimum for red light. Consequently, a given prism deviates the violet light most and the red light least.