Phase difference, intensity and the oscilloscope
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 4 practice questions, 5 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- Two swings, one ahead
- Phase difference
Read the transcript of the teaching part
Last time
Before we start: last time, in Doppler effect, electromagnetic spectrum and polarisation, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
Two swings, one ahead
Two children on neighbouring swings start together. One is a little behind, always catching up the same swing a moment later. How far behind in the cycle one oscillation lags another is its phase difference, measured as an angle.
Phase difference
Phase difference describes how much one oscillation is ahead of or behind another, as a fraction of a cycle. One full cycle is three hundred and sixty degrees, or two pi radians. A half cycle is one hundred and eighty degrees. Points that oscillate in step are in phase, with a phase difference of zero. Points in opposite step are in antiphase, one hundred and eighty degrees. For two points a distance x apart on a wave, the phase difference is x over lambda times three hundred and sixty degrees.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Cathode-ray oscilloscope · Intensity · Phase difference.
Chapter 7.1: Waves
- Progressive waves and the wave equation 6 min
- Phase difference, intensity and the oscilloscope 6 min
Also for A Level Physics 9702
Which topics come up most in A Level Physics 9702 past papers, counted from every paper since 2004: Paper 1 topic frequency, Paper 2 topic frequency.