Topic 4 – Waves — Edexcel GCSE Physics
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Topic 4 – Waves explained
A wave transfers energy and information through a medium while the medium itself stays in place.
Read the full explanation
For water waves, a floating cork or a droplet bobs up and down as a ripple passes but does not travel along with the ripple, so the water oscillates about a fixed position while the wave pattern moves outward. For sound, air particles vibrate back and forth about fixed positions and pass the disturbance to neighbours; the compression travels but the air does not move from source to ear. A smoke or dust trace, or a loudspeaker cone pushing air, shows the same point. The evidence is that the medium oscillates locally while the wave disturbance propagates, so the wave, not the water or air, travels.
Your focus
- Describe evidence that a floating object bobs in place as a water wave passes.
- Explain that air particles vibrate locally to transmit sound.
- Conclude that the wave, not the medium, travels.
Topic 4 – Waves exam tips
Marking Points
- States that a floating object on water bobs up and down as a wave passes without moving along with the wave.
- Explains that water particles oscillate about fixed positions while the wave pattern travels outward.
- States that air particles vibrate about fixed positions and pass the disturbance to neighbouring particles.
- Identifies that the compression or sound energy travels through the air while the air itself does not move from source to listener.
- Concludes that the wave transfers energy through the medium while the medium stays in place.
Examiner Tips
- 💡Name a concrete observation, such as a cork bobbing on water, to support the claim.
- 💡State clearly that the medium oscillates about a fixed position while the wave moves.
- 💡Use the word energy to describe what the wave carries through the medium.
Common Mistakes
- Claims that the water moves along with the wave; correct this by noting the cork bobs in place while the wave pattern moves.
- Asserts that air travels from the source to the ear; correct this by explaining that air particles oscillate locally and pass on the disturbance.
- Treats the medium and the wave as the same thing; correct this by separating the oscillating particles from the travelling disturbance.