Ad Banner Placeholder

Cambridge IGCSE Physics · 0625

Chapter 3: Waves — Part 1

Topic 3.1 · General properties of waves

What a wave transfers

Waves transfer energy without transferring matter. A cork on water bobs up and down as the wave passes; it is not carried along with the energy.

Wave motion can be shown with a rope or spring, and with water waves in a ripple tank.

Wave features

Wavefront
A line joining points that are in step (for example, a line along a crest).
Wavelength λ
Distance between neighbouring crests (or neighbouring compressions).
Frequency f
Number of waves per second. Unit: hertz (Hz).
Amplitude
Maximum displacement from the rest position.
Wave speed v
Distance travelled by a wavefront per unit time.

Wave equation: v = fλ

A water wave has frequency 5.0 Hz and wavelength 0.40 m. Calculate the wave speed.

Worked example: wave speed is 5.0 times 0.40 equals 2.0 metres per second
v = fλ = 2.0 m/s.

A sound wave has period 0.020 s and wavelength 4.0 m. Calculate its speed.

Worked example: frequency 50 hertz then speed 200 metres per second
f = 1/T = 50 Hz, then v = 200 m/s.

Transverse and longitudinal

In a transverse wave, vibration is at right angles to the direction of travel. Model electromagnetic waves, water waves and seismic S-waves as transverse.

In a longitudinal wave, vibration is parallel to the direction of travel. Model sound and seismic P-waves as longitudinal.

A transverse wave on a rope labelled with amplitude, wavelength, crest, trough, and the vibration direction at right angles to the direction of energy transfer.
Diagram 1: A transverse wave on a rope labelled with amplitude, wavelength, crest, trough, and the vibration direction at right angles to the direction of energy transfer.
A longitudinal wave on a spring labelled with compressions, rarefactions, wavelength, and vibration parallel to the direction of travel (sound / P-waves).
Diagram 2: A longitudinal wave on a spring labelled with compressions, rarefactions, wavelength, and vibration parallel to the direction of travel (sound / P-waves).

Reflection, refraction and diffraction

Waves can:

  • reflect at a plane surface
  • refract because speed changes (in a ripple tank, when depth changes)
  • diffract through a narrow gap and at an edge

A ripple tank shows all three: barrier for reflection; shallow region for refraction; gap and edge for diffraction.

Diffraction through a gap is more noticeable when the gap is comparable to the wavelength. Longer wavelength diffracts more at an edge.

Ripple tank: plane waves reflecting from a barrier (i = r), refracting as they enter shallower water (wavelength and speed change), and diffracting through a gap and around an edge.
Diagram 3: Ripple tank: plane waves reflecting from a barrier (i = r), refracting as they enter shallower water (wavelength and speed change), and diffracting through a gap and around an edge.

0/10

Ad Banner Placeholder