Question

Define each of the following wave phenomena, and give an example of where each occurs: (a) refraction; (b) diffraction; (c) dispersion; (d) interference.

Short answer

Refraction: Light bending in water. Diffraction: Sound spreading around a corner. Dispersion: Rainbow formation. Interference: Water wave patterns.

Step-by-step solution

- Define Refraction

Refraction is the bending of a wave as it passes from one medium into another where its speed is different. Example: Light bending when it passes from air into water.

- Define Diffraction

Diffraction is the spreading out of waves when they pass through a narrow aperture or around obstacles. Example: Sound waves bending around a corner of a building.

- Define Dispersion

Dispersion is the process in which the phase velocity of a wave depends on its frequency. Example: A rainbow is formed when light disperses through raindrops.

- Define Interference

Interference is the process where two waves superpose to form a resultant wave of greater, lower, or the same amplitude. Example: Constructive and destructive interference patterns in water waves.

Key concepts

Refraction

Refraction occurs when a wave changes direction as it passes from one medium to another. This change in direction happens because the wave's speed is different in the two media. For example, when light travels from air into water, it slows down and bends towards the normal (the imaginary line perpendicular to the surface). This bending effect is why a straw in a glass of water appears bent at the point where the air meets the water.

Refraction can also occur with other types of waves, such as sound waves, but it is most commonly observed with light waves. Understanding refraction is key in fields such as optics, helping with the creation of lenses and the correction of vision.

Diffraction

Diffraction describes the spreading out of waves as they pass through a narrow opening or go around obstacles. When waves encounter a slit or an edge, they spread out instead of traveling in straight lines. A classic example of this is hearing someone's voice around the corner of a building; sound waves can bend and spread out, allowing you to hear even without a direct line of sight.

This phenomenon is not limited to sound waves. Light waves also diffract, although the effect is more noticeable when the obstacles or openings are comparable in size to the wavelength of the light. This principle is important in various applications, including the design of audio systems and understanding the behavior of different kinds of waves.

Dispersion

Dispersion refers to the separation of waves of different frequencies as they travel. This phenomenon can be observed when different colors of light spread out to form a spectrum, like a rainbow. In a rainbow, sunlight is dispersed by raindrops, which breaks the light into its component colors, exhibiting different angles of refraction for each wavelength.

Dispersion occurs because the phase velocity of a wave depends on its frequency. In practical applications, understanding dispersion is vital in fields such as fiber optics and spectroscopy, where different wavelengths of light need to be managed effectively.

Interference

Interference is a wave phenomenon that occurs when two or more waves overlap and combine to form a new wave pattern. This can result in either constructive interference, where the waves add together to create a wave of greater amplitude, or destructive interference, where the waves cancel each other out, resulting in a wave of lower amplitude.

One common example is the interference pattern observed when two sets of water waves meet. These patterns can produce regions of more significant wave height (constructive) and regions of cancelation (destructive). Interference is a key concept in many areas of physics, and is pivotal in technologies such as noise-canceling headphones, which use destructive interference to reduce unwanted sounds.