A wave has period T, wavelength λ and amplitude A. The wave is shown on a graph of displacement x against distance d.

Question 7

A wave has period T, wavelength λ and amplitude A. The wave is shown on a graph of

displacement x against distance d.

Which graph is correctly labelled?

Reference: Past Exam Paper – March 2018 Paper 12 Q22

Solution:

Answer: A.

Period is measured in seconds while wavelength is measured in metres. That is, wavelength has the same unit as distance.

The graph provided is a graph of displacement x against distance d. The x-axis gives the distance, so a measurement on the x-axis (horizontally) gives a quantity having the same unit as distance.

So, a complete wave on the x-axis gives the wavelength, and not the period. [B and C are incorrect]

The amplitude A is the maximum displacement from the equilibrium position. [A is correct]

 
So, the distance from a peak (max) to another peak (min) vertically gives twice the amplitude (that is, 2A and not A). [D is incorrect]