Oscillations – Complete Formula & Question Profiling (JEE Main Only)
1. Periodic & Oscillatory Motion
- Periodic motion: Repeats itself after equal intervals of time
- Oscillatory motion: To-and-fro about mean position
- All oscillatory motions are periodic (not vice-versa)
2. Simple Harmonic Motion (SHM)
Defining condition:
a ∝ −x
a = −ω²x
- Restoring force always towards mean position
3. SHM Kinematics
Displacement:
x = A sin(ωt + φ)
Velocity:
v = ω√(A² − x²)
Acceleration:
a = −ω²x
Maximum values:
- vmax = ωA
- amax = ω²A
4. Time Period & Frequency
T = 2π / ω
f = 1 / T
- Independent of amplitude (for SHM)
5. Mass–Spring System
ω = √(k / m)
T = 2π√(m / k)
- Horizontal and vertical springs → same T
- Extension due to gravity does not affect T
6. Simple Pendulum
T = 2π√(l / g)
- Valid for small angular displacement
- Independent of mass
Effective length change:
- In lift accelerating upward → g' = g + a
- In lift accelerating downward → g' = g − a
7. Energy in SHM
Kinetic Energy:
K = ½ mω²(A² − x²)
Potential Energy:
U = ½ mω²x²
Total Energy:
E = ½ mω²A² = constant
- At mean position → KE max
- At extreme → PE max
8. Phase & Phase Difference
Phase: ωt + φ
- Same phase → zero phase difference
- Opposite phase → π rad
9. Damped Oscillations
- Amplitude decreases with time
- Energy continuously lost
- Time period slightly increases
10. Forced Oscillations & Resonance
- External periodic force applied
- Resonance → max amplitude when driving freq = natural freq
- At resonance → energy absorption maximum
11. JEE Main Question Profiling
| Question Type | JEE Tests | Common Trap |
|---|---|---|
| SHM definition | a ∝ −x condition | Ignoring negative sign |
| Energy based MCQ | KE–PE exchange | Wrong position substitution |
| Spring–block | k/m dependence | Gravity affecting T |
| Pendulum in lift | Effective g concept | Sign error in g' |
| Resonance | Frequency matching | Confusing amplitude & energy |
| Phase questions | Trigonometric understanding | Using degrees instead of radians |
12. JEE Main Weightage Insight
- 1–2 MCQs in most sessions
- Formula-heavy, concept-light
- Very high scoring chapter
StudyBeacon • JEE Main Physics • Oscillation Master Sheet
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