Concept Notes – Waves & Resonance (Physics)
⚙️ Waves
- A wave is a disturbance that transfers energy without transfer of matter.
- Types of Waves:
- Mechanical waves – need a medium (sound, water).
- Electromagnetic waves – no medium required (light, radio).
- Mechanical waves further:
- Transverse waves → Particles vibrate ⟂ to wave propagation (example: water surface waves).
- Longitudinal waves → Particles vibrate ∥ to wave propagation (example: sound waves).
📌 Important Terms:
- Wavelength (λ) = distance between two successive crests/troughs.
- Frequency (f) = number of vibrations per second.
- Time Period (T) = 1/f.
- Wave velocity (v):
latexlatexlatex v = f \times \lambda [/latex]
⚙️ Resonance
- Resonance = Phenomenon where a body vibrates with maximum amplitude when frequency of external force = natural frequency of body.
- Examples:
- Tuning fork making another fork vibrate.
- Swing going higher when pushed at correct intervals.
- Breaking of glass by loud sound at resonant frequency.
📌 Natural frequency (f₀): 
where k = stiffness (spring constant), m = mass.
⚙️ Formulas (Quick Reference)
- Velocity of wave:
- Time period:
- Natural frequency of simple pendulum:
- Natural frequency of spring–mass system:
🔟 10 Expected MCQs – ECET 2026 (Physics: Waves & Resonance)
Q1. In a transverse wave, particle vibration is:
A) Parallel to wave direction
B) Perpendicular to wave direction
C) At 45° to wave direction
D) Random
Q2. Which of the following is a longitudinal wave?
A) Light
B) Sound
C) Water surface wave
D) Radio wave
Q3. Relation between velocity, wavelength, and frequency is:
A) v = λ / f
B) v = f × λ
C) v = λ – f
D) v = λ + f
Q4. Resonance occurs when:
A) External frequency > natural frequency
B) External frequency < natural frequency
C) External frequency = natural frequency
D) External force = zero
Q5. Which is not an example of resonance?
A) Swing in playground
B) Glass breaking due to sound
C) Moon revolving around Earth
D) Tuning fork vibration
Q6. SI unit of frequency is:
A) Second
B) Hertz
C) Joule
D) Newton
Q7. In sound waves, compression and rarefaction are features of:
A) Transverse waves
B) Longitudinal waves
C) Stationary waves
D) Electromagnetic waves
Q8. Formula for natural frequency of pendulum is:
A) f = 2π√(l/g)
B) f = (1/2π)√(g/l)
C) f = (1/2π)√(l/g)
D) f = √(g/l)
Q9. Maximum amplitude at resonance is due to:
A) Zero damping
B) External force equal to weight
C) Equal frequencies
D) Strong medium
Q10. Which wave does not require a medium?
A) Sound
B) Water wave
C) Light
D) Seismic
✅ Answer Key
| Q.No | Answer |
|---|---|
| Q1 | B |
| Q2 | B |
| Q3 | B |
| Q4 | C |
| Q5 | C |
| Q6 | B |
| Q7 | B |
| Q8 | B |
| Q9 | C |
| Q10 | C |
🧠 Explanations
- Q1 → B: Transverse waves have vibrations ⟂ to wave motion.
- Q2 → B: Sound is longitudinal.
- Q3 → B: v = f × λ is standard wave relation.
- Q4 → C: Resonance when frequencies match.
- Q5 → C: Moon revolution is gravitational, not resonance.
- Q6 → B: Hertz (Hz) is SI unit of frequency.
- Q7 → B: Longitudinal sound waves have compressions and rarefactions.
- Q8 → B: f = (1/2π)√(g/l) is correct.
- Q9 → C: Amplitude max when external = natural frequency.
- Q10 → C: Light (EM waves) need no medium.
🎯 Why This Matters for ECET 2026
Physics always has 2–3 direct questions from Waves & Resonance. Formulas are simple but repeatedly asked. By practicing both concept + MCQs, students can score easy marks. Also, resonance is an important real-life concept (engineering, music, bridges, instruments).
📲 CTA
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