What are wavefronts?
4 marks · HardA science teacher explains that 'wavefronts help us understand how energy moves in waves.'
Explain what is meant by a wavefront. Your answer should include how particles move and what 'in phase' means.
Describe how you could use the concept of wavefronts to find the direction in which a wave is moving in water.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) A wavefront is a line joining points on a wave that are in phase (vibrating in the same way at the same instant). Particles on a wavefront move in the same pattern or position at the same time. · must show Refer to 'in phase', Particles having same motion
(b) The wave moves at right angles to the wavefronts. By observing the wavefronts (lines of ripples in water), you can identify which way the wave energy is moving: it travels perpendicular to the wavefronts. · must show Energy moves perpendicular to wavefronts, Observation linked to direction
Common mistakes: Confusing wavefront with crest only; Incorrect direction of energy
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Marking points
M1 (a) · 1 mark · Defines wavefront as line (or surface) of points vibrating in phase/on same stage.
A1 (a) · 1 mark · Explains 'in phase': same motion/same part of vibration for particles.
M2 (b) · 1 mark · States wave energy travels at right angles/perpendicular to wavefronts.
B1 (b) · 1 mark · Describes using observation of wavefronts/ripples to determine energy direction.
Worked solution
(a) A wavefront is a line (or surface) connecting all points on a wave that are in phase. This means all the particles along the wavefront are vibrating in exactly the same way or are at the same stage of oscillation.
(b) In water waves, you can observe the lines of ripples as wavefronts. The direction of wave travel, and of energy transfer, is perpendicular (at right angles) to the wavefronts. Thus, by looking at the orientation of the wavefronts, you can deduce that the wave is moving in the direction normal to these lines.