Properties of Waves
5 marks · NormalA ripple tank is used to study water waves. When the frequency of the motor is increased, the spacing of the wavefronts changes.
Describe, using the terms wavelength and frequency, how the spacing between wavefronts changes as the frequency is increased.
The distance from a crest to the next crest in the tank is measured to be . The frequency of vibration is . Calculate the speed of the water waves. Give your answer in .
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) As the frequency increases, the spacing between wavefronts (wavelength) decreases. · must show frequency and wavelength relationship
(b) 0.48 m/s · must show conversion of wavelength to m, correct substitution, wave speed calculation
Common mistakes: Incorrectly converting mm to m; Using period instead of frequency
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States that as frequency increases, wavelength decreases (or spacing between wavefronts gets smaller).
B2 (a) · 1 mark · Uses the terms frequency and wavelength correctly.
M1 (b) · 1 mark · Converts 12 mm to 0.012 m correctly.
M2 (b) · 1 mark · Writes down v = f × λ or substitutes values into the wave equation.
A1 (b) · 1 mark · Correct final answer for speed to 2 significant figures (0.48 m/s). (follow-through)
Worked solution
a) According to the wave equation, for a constant wave speed, as the frequency increases, the wavelength decreases. This means the wavefronts become closer together.
b) Given:,