Unit 12: Waves — Short Questions

Waves transfer energy from one place to another without transferring matter. This is a fundamental characteristic of all waves, whether they are mechanical waves like sound or electromagnetic waves like light. Particles of the medium vibrate but remain in their original positions while passing energy to neighboring particles.

Examples of mechanical waves are:
(i) Sound waves
(ii) Water waves
These waves require a material medium to travel.

Electromagnetic waves can travel through vacuum. They do not require a material medium. Light and radio waves are common examples.

Transverse Waves

• Types of waves in which Particles vibrate perpendicular to the direction of wave travel are called transverse waves
• They have crests and troughs
• Examples: Water waves, electromagnetic waves.

Longitudinal Waves

• Types of waves in which Particles vibrate parallel to the direction of wave travel are called Longitudinal Waves
• They have compressions and rarefactions.
• Examples: Sound waves, seismic P-waves.

The distance between two consecutive corresponding points on adjacent waves, such as crest to crest or compression to compression is called Wavelength.
Symbol: λ
Unit: metre (m)

The number of complete cycles that pass a fixed point in one second is called frequency.
Symbol: f
Unit: hertz (Hz)

A tsunami is caused by sudden disturbances under the sea. These include underwater earthquakes, volcanic eruptions, or landslides. Such disturbances displace a large volume of water.

Waves transfer energy through the vibration of particles in a medium. The particles oscillate in place and pass energy to neighboring particles without moving forward themselves. For example, when a stone is dropped in water, ripples spread outward carrying energy, but the water molecules do not travel with the ripples.

Sound is a mechanical wave that requires a material medium to travel. Space is a vacuum with no particles to vibrate. Therefore, sound cannot travel through space.

Mechanical waves need a medium to travel, such as sound waves or water waves. Electromagnetic waves do not require a medium and can travel through vacuum, such as light and radio waves.

Transverse waves are waves where the particles of the medium vibrate perpendicular to the direction of wave travel. This creates crests and troughs. Examples include water waves and electromagnetic waves like light.

Longitudinal waves are waves where particles vibrate parallel to the direction of wave travel, forming compressions and rarefactions. Sound waves are longitudinal. Unlike transverse waves, they do not have crests and troughs, seismic P-waves etc.

Wavelength is the distance between two consecutive crests or compressions. Frequency is the number of waves passing a point per second. They are related to wave speed by the formula:
v = fλ

Amplitude indicates the energy carried by a wave. Larger amplitude means more energy. For example, a loud sound has higher amplitude in its sound wave compared to a soft sound.

A wave front is an imaginary surface where all points vibrate in the same phase. It helps visualize how waves spread out and interact with obstacles, such as during reflection or refraction.

Crest is the highest point above mean position in transverse waves; trough is the lowest point below mean position.
Compression is where particles are close together (high pressure) in longitudinal waves; rarefaction is where they are spread apart (low pressure). These terms describe wave structure.

Reflection occurs when waves bounce back after hitting a barrier. The angle of incidence equals the angle of reflection. An example is an echo, where sound waves reflect off walls or mountains.

Refraction is the bending of waves when they pass from one medium to another due to a change in speed. It occurs because waves travel at different speeds in different media, like light bending when entering water.

Diffraction is the spreading of waves as they pass through a gap or around an obstacle. If the gap size is smaller than or equal to the wavelength, diffraction is more pronounced. Sound diffracts around corners, allowing us to hear even without direct line of sight.

Seismic waves are waves generated by earthquakes or volcanic activity that travel through the Earth. The two main types are P-waves (longitudinal) and S-waves (transverse).

Tsunamis are formed by underwater disturbances such as earthquakes, volcanic eruptions, or landslides. These events displace large volumes of water, generating long, fast-moving waves that grow in height as they approach shallow coasts.

Sound cannot travel through space, but light can.
Reason
Sound waves are mechanical waves and require a material medium. Space is a vacuum with no medium, so sound cannot travel. Light waves are electromagnetic waves that do not require a medium and can travel through vacuum.

It is a transverse wave.
Reason
When the rope is shaken up and down, the wave travels horizontally along the rope. The particles of the rope vibrate up and down (perpendicular to the direction of wave travel). The wave transfers energy along the rope without moving the rope forward. This is why it is a transverse wave.

The amplitude of a wave is directly related to the energy it carries. A wave with greater amplitude carries more energy.
Reason
Amplitude is the maximum displacement of a point on the wave from its rest position. Higher amplitude means the wave disturbs the medium more, requiring and transferring more energy.
Example
A loud sound (like a shout) has a higher amplitude and carries more energy than a soft whisper, which has a lower amplitude.

We hear sound behind a wall due to diffraction.
Reason
Diffraction is the bending and spreading of waves as they pass through a narrow gap or around an obstacle. Sound waves have relatively long wavelengths that diffract around corners and obstacles like walls, allowing sound to reach us even without direct line of sight.

The wave will show maximum diffraction and spread out circularly.
Reason
When the gap size is smaller than the wavelength, diffraction is maximum. The wave bends strongly at the edges of the gap and spreads out in a circular pattern on the other side. It is almost as if the gap itself were a new source of circular waves.