Progressive waves

WPH12Topic 2.14 questions

Wave properties, the wave equation, longitudinal and transverse waves, and intensity of radiation.

Specification points

Understand the terms amplitude, frequency, period, speed and wavelength
Be able to use the wave equation $v = f\lambda$
Be able to describe longitudinal waves in terms of pressure variation and the displacement of molecules
Be able to describe transverse waves

Be able to draw and interpret graphs representing transverse and longitudinal waves including standing/stationary waves

CORE PRACTICAL 4: Determine the speed of sound in air using a 2-beam oscilloscope, signal generator, speaker and microphone

Be able to use the equation for the intensity of radiation $I = \frac{P}{A}$

Get a plain-language explanation, a worked example and the usual mistake.

Sign in to get a plain-language explanation of any specification point.

Original practice questions written in the style of the exam.

Question 12 marks
Explain the difference between a transverse wave and a longitudinal wave. Give one example of each.
Mark scheme
- Transverse: oscillations perpendicular to the direction of energy transfer; longitudinal: oscillations parallel to the direction of energy transfer (1)
- Valid examples, e.g. transverse — light/any EM wave/water ripples; longitudinal — sound/P-waves (1)
Question 23 marks
A microphone connected to an oscilloscope detects a sound wave. One complete cycle of the trace occupies 4.0 horizontal divisions, and the time-base is set to $0.50\,\text{ms div}^{-1}$ . The speed of sound in air is $340\,\text{m s}^{-1}$ .

Calculate the wavelength of the sound.
Mark scheme
- Period $T = 4.0 \times 0.50\,\text{ms} = 2.0 \times 10^{-3}\,\text{s}$ (1)
- (1)

f = 1/T = 500\,\text{Hz}

f = 1/ T = 500 Hz

\lambda = v/f = 340/500 = 0.68\,\text{m}

(1)