AIIMS 2006 Physics Refraction MCQ Question

Explanation of Refraction and the Correct Answer:

When light waves pass from one medium to another, they change direction—a phenomenon known as refraction. This bending occurs primarily due to the change in the speed of light as it enters a different medium.

Why the Correct Answer is C (the speed is different):

Light travels at different speeds in different media. This speed change is influenced by the optical density of the materials involved. The speed of light in a vacuum is denoted as $c$, and in a medium, the speed of light $v$ can be expressed as:

$v = \frac{c}{n}$

where $n$ is the refractive index of the medium. The refractive index is defined as:

$n = \frac{\text{speed of light in vacuum}}{\text{speed of light in medium}}$

As light moves from a medium with a lower refractive index (such as air) to one with a higher refractive index (like glass), its speed decreases. This decrease in speed causes the light to bend toward the normal line (the perpendicular line to the surface at the point of incidence). Conversely, when light exits a denser medium to a less dense one, it speeds up and bends away from the normal.

Why Other Options are Incorrect:

A) The frequency is different: The frequency of a light wave remains constant when it passes from one medium to another. It is the product of the wavelength and the speed of light, given by the equation:

$f = \frac{v}{\lambda}$

where $f$ is frequency, $v$ is the speed of light, and $\lambda$ is the wavelength. Although the speed and wavelength change with refraction, the frequency does not change as it is determined by the source of the light.

B) The coefficient of elasticity is different: The coefficient of elasticity is a property more relevant to mechanical waves (like sound) rather than electromagnetic waves like light. While the medium's properties (including elasticity) affect its refractive index, it does not directly explain the bending of light during refraction.

D) The amplitude is smaller: The amplitude of light does change as it enters a different medium, but this does not affect the bending of light. Amplitude relates to the intensity or brightness of the light, but it does not influence the path of the light rays as they refract.

Conclusion:

In summary, the bending of light waves during refraction is primarily due to the change in speed as they transition from one medium to another. The correct answer (C) highlights this key principle, while the other options misrepresent the factors affecting refraction. Understanding the relationship between speed, refractive index, and light behavior is crucial in the study of optics.