This checkpoint covers Lessons 1 to 4: wave types, wave properties, graph reading, intensity, inverse square law, superposition and interference.
Checkpoint Assessment
1. Which wave does not require a medium?
2. A displacement-time graph gives direct information about:
3. A wave has frequency 5 Hz and wavelength 2 m. Its speed is:
4. If distance from a point source doubles, intensity becomes:
5. If amplitude doubles, intensity becomes:
6. Two waves interfere constructively when path difference is:
7. Coherent sources must have:
8. Two pulses with displacements +3 cm and −5 cm overlap. The resultant displacement is:
9. Explain the difference between a mechanical wave and an electromagnetic wave, using one example of each. 3 MARKS
10. A wave travels at 15 m/s and has frequency 3 Hz. Calculate its wavelength. 3 MARKS
11. Explain why a stable two-source interference pattern requires coherent sources, and state the path-difference conditions for constructive and destructive interference. 4 MARKS
1. A — light is electromagnetic.
2. C — displacement-time gives period.
3. D — $v = f\lambda = 5 \times 2 = 10\ \text{m/s}$.
4. B — doubling distance gives one quarter intensity.
5. A — intensity depends on amplitude squared.
6. C — constructive interference occurs for $n\lambda$.
7. D — coherence means same frequency and constant phase relationship.
8. B — resultant = +3 + (−5) = −2 cm.
Q9 (3 marks): A mechanical wave requires a medium, such as sound in air or a pulse on a rope. An electromagnetic wave does not require a medium and can travel through vacuum, such as visible light or radio waves.
Q10 (3 marks): Rearranging $v = f\lambda$ gives $\lambda = v/f = 15/3 = 5\ \text{m}$.
Q11 (4 marks): A stable interference pattern requires coherent sources because the sources must keep the same frequency and a constant phase relationship. Otherwise the reinforcement and cancellation points move around and the pattern is not steady. Constructive interference occurs when path difference equals $n\lambda$. Destructive interference occurs when path difference equals $(n + 1/2)\lambda$.
Tick when you have finished the checkpoint and checked the answers.