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10
v = 5 × 2.
Class 11 · English Version · Physics
Waves, light and sound
Relate wave speed, frequency, refraction and interference.
Shared cross-level core and stretch unit. Start with the core questions, then use the stretch example for deeper work. The same unit is available in related class and board pathways; it is not a full grade-specific or examination-specification course. A teacher should select the appropriate depth and further topics.
Learn the idea
Wave speed v = fλ links frequency f and wavelength λ. Frequency counts cycles per second. A wave crossing into a different medium keeps its frequency while speed and wavelength can change. Superposition adds displacements where waves overlap; persistent interference also requires an appropriate phase relationship.
Worked example
A wave at 50 Hz with wavelength 0.4 m travels at 20 m/s. If its speed becomes 10 m/s in a new medium, its unchanged 50 Hz frequency gives wavelength 0.2 m.
- Identify the medium and quantities.
- Keep frequency fixed across a stationary boundary.
- Explain the physical relationship as well as the calculation.
Stretch example
For double-slit light interference at small angles, fringe spacing w = λD/a. With λ = 500 nm, D = 2 m and a = 0.5 mm, w = 0.002 m = 2 mm.
Your written practice
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170
f = v/λ.
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yes
Sound is a mechanical wave.
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Transverse displacement is perpendicular to propagation; longitudinal displacement is parallel.
Compare direction of oscillation with propagation.
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Light is electromagnetic; sound needs mechanical interactions in matter.
Identify the different mechanisms.
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2
Spacing is directly proportional to D.
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Sources need the same frequency and a stable phase difference; the setup must allow overlapping waves.
Mention coherence and overlap; practical visibility can need comparable amplitudes.
Wave diagram
Draw two labelled wave profiles and explain one constructive and one destructive overlap.
Review with a guardian or teacher
- Use displacement axes.
- State relative phase.
- Distinguish a diagram from an actual measurement.
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