Question

A medium is said to be dispersive, if

• A. Light of different wavelength propagate at different speeds
• B. Light of different wavelengths propagates at same speed but has different frequencies
• C. Light is gradually bent rather than sharply refracted at an interface between the medium and air
• D. Light is never totally internally reflected

Answer 1

The correct option is A Light of different wavelength propagate at different speeds

Dispersion take place because the refractive index of medium for different colour is different, for example, red light bends less than violet, refractive index of the material of the prism for red light is less than that for violet light. Equivalently, we can say that red light travels faster than violet light in a glass prism.