Phase Difference and Amplitude
Phase Difference and Amplitude
- Phase compares positions within a cycle. Amplitude measures one centre-to-extreme distance.
Phase says where the object is in its cycle
- Two objects can have the same frequency but reach their turning points at different times. They have a phase difference.
Definition
1 markWhat is meant by phase difference?
Model answer: The fraction of a complete cycle by which one oscillation leads or lags another.
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Symbols
- = phase difference (rad)
- = time shift between matching points (s)
- = period (s)
- Use matching points on the two graphs: for example, two upward crossings of the equilibrium line.
- A quarter-cycle shift is 90° or one-half pi radians. A half-cycle shift is 180° or pi radians.
Common mistake
Do not compare a peak on one graph with a zero crossing on the other. Compare the same point in the cycle and the same direction of motion.
Three common amplitude questions
Two extreme positions
Take half of the full range.
Amplitude is centre to one extreme.
Distance travelled in one cycle
Divide the distance by four.
One cycle has four centre-to-extreme journeys.
Height or depth from a fixed point
Find the mid-value first.
The graph's zero may not be equilibrium.
These forms appear directly in recent Paper 4 questions (9702/42/F/M/24 Q3(a)) (9702/41/O/N/24 Q4(b)(i)).