Chapter 13: Waves
2 Two points on a progressive wave are 25 cm apart and differ in phase by 90°. a Explain how this information shows that the wavelength of the wave is 100 cm. b Determine the distance between two points on the wave that have a phase difference of 270°. c Two points on the wave are separated by a distance of 15 cm. Calculate the phase difference between the two points. 3 Explain in your own words what is meant by a phase difference. 4 This diagram shows the variation of displacement with time of two points A and B on the same rope: Displacement A B
00
Time
a Compare the amplitude of the motions of A and B. b Compare the frequency of the motions of A and B. c Compare the phases of the motions of A and B. 77
Exercise 13.3 Wave intensity, measuring time and the electromagnetic spectrum This exercise involves some more complex ideas, such as intensity, the electromagnetic spectrum and using the time base on an oscilloscope to measure a time. 1 Two waves of the same frequency have amplitudes of 1.5 cm and 3.0 cm. intensity of wave of amplitude 1.5 cm Calculate the ratio intensity of wave of amplitude 3.0 cm Remember: intensity � (amplitude)2. 2 A wave has amplitude A 0 and intensity I0. The other waves in this table have the same frequency but different intensities and amplitudes:
initial wave wave A
Amplitude
Intensity
A0
I0
1 2
A0 1 I 2 0
wave B wave C wave D
3 A0 16 I0
Copy and complete the table, determining the missing amplitudes and intensities, in terms of A 0 and I0.