General Properties Of Waves

Waves Transfer Energy, Not Matter

• Waves transfer energy from one place to another without transferring matter.
• For example, sound waves travel through air, but the air molecules themselves do not travel with the wave.
• A floating object on water bobs up and down as waves pass, but does not move horizontally with the wave.

A toy duck floats on water. Waves pass underneath it. Which statement best describes the duck's motion?

• The duck moves with the wave in the direction of energy transfer.
• The duck moves up and down but stays in roughly the same position.
• The duck moves sideways but not up and down.
• The duck does not move at all.

Features of a Wave

• Amplitude: maximum displacement from the undisturbed position (measured in metres).
• Wavelength (λ): distance from one point on the wave to the same point on the next wave (measured in metres).
• Frequency (f): number of waves passing a point per second (measured in hertz, Hz).
• Crest: highest point above undisturbed position. Trough: lowest point below undisturbed position.

Which of the following is the correct definition of wavelength?

• The distance from a crest to a trough.
• The distance from one point on a wave to the same point on the next wave.
• The number of waves passing a point per second.
• The maximum displacement from the undisturbed position.

The Wave Equation

• Wave speed (v) = frequency (f) × wavelength (λ).
• v is measured in m/s, f in Hz, λ in m.
• The period (T) is the time for one complete wave: T = 1/f, so f = 1/T.

A wave has a speed of 2 m/s and a wavelength of 0.5 m. Its frequency is ____ Hz.

Transverse vs Longitudinal Waves

• Transverse waves: vibrations perpendicular to direction of energy transfer. Examples: light, water ripples, S-waves.
• Longitudinal waves: vibrations parallel to direction of energy transfer. Examples: sound, P-waves.
• Transverse waves have crests and troughs; longitudinal waves have compressions and rarefactions.

Which of these are transverse waves?

• Sound waves
• Light waves
• Water ripples
• Seismic P-waves

Reflection, Refraction, and Diffraction

• Reflection: wave bounces off a surface; angle of incidence = angle of reflection.
• Refraction: wave changes speed (and direction) when entering a different medium; wavelength changes, frequency stays the same.
• Diffraction: wave spreads out when passing through a gap or around an edge; most noticeable when gap size ≈ wavelength.

When a water wave passes from deep to shallow water, its speed decreases. What happens to its wavelength?

• It increases.
• It decreases.
• It stays the same.
• It becomes zero.

Ripple Tank Experiments

• A ripple tank uses a motor to generate water waves on a shallow tray.
• Reflection: place a barrier; waves reflect obeying the law of reflection.
• Refraction: place a glass block to create shallow region; waves slow down and wavelength decreases.
• Diffraction: use barriers with gaps; diffraction is greater when gap is similar to wavelength.

In a ripple tank, the ____ of the motor affects the wavelength of the waves: higher frequency gives ____ wavelength.

Diffraction and Gap Size

• Diffraction is most prominent when the gap width is approximately equal to the wavelength.
• If the gap is much larger than the wavelength, diffraction is negligible.
• Longer wavelengths diffract more than shorter wavelengths around edges.

A wave of wavelength 2 cm passes through a gap of width 10 cm. What can you say about the diffraction?

• The wave spreads out a lot.
• The wave spreads out very little.
• The wave is reflected.
• The wave changes speed.

Longitudinal Waves: Compressions and Rarefactions

• In a longitudinal wave, particles vibrate parallel to the direction of energy transfer.
• Compressions: regions where particles are close together (high pressure).
• Rarefactions: regions where particles are spread apart (low pressure).
• Wavelength is measured from the centre of one compression to the centre of the next.

In a longitudinal wave, the regions where particles are closest together are called ____.

Wave Speed in Different Media

• Wave speed depends on the medium (e.g., sound travels faster in solids than in gases).
• When a wave enters a new medium, its speed and wavelength change, but frequency remains constant.
• For light, speed is fastest in a vacuum; it slows down in denser media like glass or water.

A light ray travels from air into glass. Which property of the wave remains unchanged?

• Speed
• Wavelength
• Frequency
• Direction