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.

Type

Multiple choice Written

Difficulty

Easy Medium Hard

Question 1

Paper 2Hard10 marks

A small mass attached to a vertical spring oscillates in simple harmonic motion between upper turning point U and lower turning point L, passing through equilibrium position O. The spring remains stretched throughout the motion. Consider the mass, spring and Earth as the system. Air resistance and other resistive forces are negligible. The mass is released from rest at U. Its mechanical energy consists of kinetic, gravitational potential and elastic potential energy.

(a)

As the mass moves from U to L, state how its gravitational potential energy and elastic potential energy change.

[2]

(b)

At which position, U, O or L, is the kinetic energy greatest?

[1]

(c)

Compare the total potential energy of the system at U and L. Explain your answer with reference to the gravitational and elastic potential energies.

[3]

(d)

A student says: “The gravitational potential energy is lower at L than at U, so mechanical energy has been lost during the motion from U to L.” Evaluate this statement by describing the energy changes over U→O→L→U.

[4]

Question 2

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 3

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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