Retrieval Practice
Forced Vibrations & Resonance — AQA A-Level Physics
Q1. Define damping.
The reduction in energy and amplitude of oscillations due to resistive forces acting on the oscillating system.
Q2. Name the three types of damping and give one example of each.
- Light damping: swinging pendulum in air.
- Critical damping: car suspension.
- Heavy damping: door closer mechanism.
Q3. What happens to the frequency of oscillation as a lightly damped system loses amplitude?
- The frequency stays the same.
- Only the amplitude decreases.
- The time period remains constant.
Q4. Define critical damping.
The degree of damping where the system returns to equilibrium in the shortest possible time without any oscillation.
Q5. Distinguish between free and forced oscillations.
- Free: only internal forces, no energy input, oscillates at natural frequency.
- Forced: periodic external driving force, energy input, oscillates at the driving frequency.
Q6. Define resonance.
Resonance occurs when the driving frequency equals the natural frequency of a system, causing the amplitude to reach a maximum.
Q7. Describe three effects of increased damping on a resonance curve.
(1) Peak amplitude decreases. (2) The peak broadens. (3) The peak shifts slightly to the left of f_0.
Q8. Does the natural frequency change when damping is increased?
- No.
- The natural frequency f_0 is a property of the system and does not change with damping.
Q9. In Barton's pendulums, which pendulum has the largest amplitude and why?
- The pendulum with the same length as the driving pendulum.
- Its natural frequency equals the driving frequency, so resonance occurs.
Q10. What is the phase difference between the resonating pendulum and the driver in Barton's pendulums?
- pi/2 radians (90 degrees).
- The resonating pendulum lags the driver by a quarter cycle.
Q11. Give two useful applications of resonance.
- Organ pipes (air resonates to produce sound).
- Radio tuning (circuit resonates at broadcast frequency).