IB Physics SL Theme C: Wave behaviour questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

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Question 1

Multiple choiceEasy1 mark

A string supports a standing wave. Points P and Q are antinodes immediately on opposite sides of the same displacement node. What is the phase difference between the oscillations of P and Q, in radians?

Show answer and explanation

Answer: C. Adjacent antinodes separated by a displacement node oscillate in antiphase: when one is at maximum positive displacement, the other is at maximum negative displacement. This is a half-cycle separation, so $\Delta\phi = 2\pi(1/2) = \pi\ \text{rad}$ A: treats the two points as oscillating in phase. B: assigns a quarter-cycle separation instead of opposite-phase motion. D: assigns a three-quarter-cycle separation instead of a half-cycle. Remember: antinodes in neighbouring segments separated by a node oscillate in antiphase.

Question 2

Paper 2Easy9 marks

A sound source emits a steady tone into still air. Its emitted frequency is $f_s$ in both situations shown in Figure 1. The figure shows successive wavefronts along the line of motion at one instant. In A, the source is fixed and O moves as indicated. In B, the source moves as indicated while O₁ and O₂ are stationary. The diagrams are schematic; compare only the separations of adjacent wavefronts.

(a)

Describe the spacing of the wavefronts in A and state whether motion of O changes their spacing in the air.

[2]

(b)

Explain whether the frequency heard by O is higher or lower than $f_s$

[2]

(c)

In B, state the direction in which the source moves and compare the wavefront spacing ahead of and behind it.

[3]

(d)

State whether O₁ hears a frequency higher or lower than $f_s$

[1]

(e)

State whether O₂ hears a frequency higher or lower than $f_s$

[1]

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