In the dispersion of white light by a common glass prism, which one among the following is correct ?

When white light enters a glass prism, it undergoes dispersion because different colors of light travel at different speeds in the medium. The refractive index (n) of glass is wavelength-dependent, as described by Cauchy's equation.

• Wavelength and Speed: Blue light has a shorter wavelength than red light. In glass, a shorter wavelength experiences a higher refractive index. Since the speed of light in a medium is v = c/n, blue light travels at a lower speed than red light.
• Deviation: The degree of bending or deviation is directly proportional to the refractive index. Because blue light has a higher refractive index (and lower speed) in the prism, it deviates the most from its original path.

In contrast, red light has the longest wavelength, highest speed in the prism, and deviates the least. Therefore, Option D is correct.