Class 10 Physics — Chapter 1: Waves (Detailed Notes)
1. What is a Wave?
A wave is a disturbance that transfers energy from one place to another without the net movement of matter.
2. Classification of Waves
Mechanical vs Electromagnetic
- Mechanical waves require a medium (e.g., sound, water waves).
- Electromagnetic waves do not require a medium (e.g., light, radio waves).
Transverse vs Longitudinal
- Transverse: particle motion ⟂ direction of propagation (crest, trough).
- Longitudinal: particle motion ∥ direction of propagation (compression, rarefaction).
3. Important Terms
- Wavelength (λ), Frequency (f), Time period (T), Amplitude (A), Wave speed (v)
v = f × λ
f = 1 / T
T = 1 / f
f = 1 / T
T = 1 / f
4. Sound Waves
Sound is a longitudinal mechanical wave. Speed in air ~343 m/s, water ~1480 m/s, steel ~5000 m/s.
5. Echo (Reflection of Sound)
An echo is a reflected sound heard separately from the original sound.
- Minimum distance of reflecting surface ≈ 17 m (for 0.1 s delay)
- Formula: d = (v × t)/2
Example: Echo heard after 6 s, v = 340 m/s → d = 340×6/2 = 1020 m
6. Applications of Echo
- SONAR, Ultrasound imaging, Animal echolocation
7. Solved Numerical Examples
1) Wave: λ=0.5 m, f=200 Hz → v = 200×0.5 = 100 m/s
2) Echo: t=4 s, v=340 m/s → d = 340×4/2 = 680 m
2) Echo: t=4 s, v=340 m/s → d = 340×4/2 = 680 m
8. Practice Questions
- Frequency=60 Hz, speed=300 m/s → wavelength?
- Echo heard 0.5 s later, v=343 m/s → distance?
Answers: 1) λ=300/60=5 m, 2) d=343×0.5/2=85.75 m
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