Question

When monochromatic light is refracted as it passes from air to glass, which of the following does NOT remain the same? (Note: Assume that the wave is fully transmitted.) (A) Wavelength (B) Frequency (C) Amplitude (D) Period

Short answer

The wavelength does not remain the same.

Step-by-step solution

- Understand the concepts

When light passes from one medium to another (e.g., from air to glass), some properties of the wave change while others remain constant. Specifically, frequency and period of the wave remain constant because they are determined by the source of the light.

- Identify the changing properties

The wavelength and speed of light change as it passes through different media. The wavelength in glass differs from the wavelength in air since the speed of light decreases in a denser medium.

- Recall amplitude change conditions

The amplitude can change if there is partial reflection or absorption of the wave, but if the wave is fully transmitted as per the problem's condition, amplitude stays the same.

- Conclusion

Combining the information, we see that the wavelength of light changes when moving from air to glass, but the frequency, period, and amplitude (since it's fully transmitted) remain constant.

Key concepts

Wavelength Change

When light enters a different medium, like moving from air to glass, its wavelength changes. This happens because the speed of light varies depending on the medium it travels through. The relationship between the speed of light, its wavelength, and its frequency is given by the equation: \[ v = f \lambda \]where \( v \) is the speed of light, \( f \) is the frequency, and \( \lambda \) is the wavelength. As light enters glass from air, its speed decreases. Since the frequency remains the same (determined by the source), the wavelength must adjust to maintain the relationship. Thus, light in glass has a shorter wavelength compared to light in air.

Frequency Constancy

A crucial point about light refraction is that the frequency of light remains constant as it passes from one medium to another. The frequency is intrinsic to the light wave and is determined by its source. This means, whether the light is traveling through air, glass, or any other medium, the number of wave crests passing a fixed point per second (frequency) won't change.
This constancy is important because even though the speed and wavelength of the light can alter, the frequency staying the same ensures that the light retains its original color and other properties tied to its source frequency.

Light Transmission

When light fully transmits through a medium, without being reflected or absorbed, its amplitude remains the same. This means that the energy of the light wave remains consistent as it passes through different materials.
Light transmission through materials like glass can be visualized as a process where the light wave neither loses nor gains intensity, maintaining a steady amplitude throughout its journey as long as the transmission is complete and no part of the wave is lost.

Medium Properties

Different media have unique properties that affect how light travels through them. The most notable property is the refractive index, which is a measure of how much the speed of light is reduced inside the medium. The higher the refractive index, the slower the speed of light in that medium.
This change in speed causes the light to bend at the boundary between two media - this bending is what we call refraction. The extent of refraction depends on the angles of incidence and transmission and the indices of refraction of the two media. By understanding these properties, we can predict and explain how and why light behaves as it travels through different substances.