IB Physics SL C 2 Wave Model Questions

In IB Physics SL C.2, use particle-motion sketches to distinguish wave types, calculate speed or wavelength from v=fλ, and explain how sound or light propagates.

Exam points

Classify transverse and longitudinal waves from particle oscillation relative to energy propagation.
Read displacement-position/time graphs and use v = fλ = λ/T to calculate speed, wavelength, frequency or period.
Describe sound as a mechanical longitudinal wave with particle motion, compressions and rarefactions.
Describe transverse E/B fields, vacuum speed c and wavelength scales in electromagnetic-wave questions.
Explain energy transfer without net matter motion and relate amplitude or speed to wave intensity/power.

Covered syllabus points

C.2.1—Transverse and longitudinal travelling waves C.2.2—Wave quantities and wave equation C.2.3—Nature of sound waves C.2.4—Nature of electromagnetic waves C.2.5—Mechanical and electromagnetic wave models

[Maximum number: 4]

(a)

Outline what is meant by a travelling wave.

[ 2 ]

(b)

A loudspeaker emits sound of frequency 210 Hz into a pipe with one open and one closed end. The diagram shows a representation of the standing wave established in the pipe.

[ 2 ]

(i)

Calculate the speed of sound in the pipe stating the answer to an appropriate number of significant figures.

[ 2 ]

$c=\ll \lambda f=1.60 \times 210 \Rightarrow \gg 336$ OR $340 \ll \mathrm{~m} \mathrm{~s}^{-1} \gg$
Any answer to 2 OR 3 s.f.

Marking guidance:

Allow ECF from incorrect wavelength in bii)

[Maximum number: 6]

This question is in two parts. Part 1 is about the nuclear model of the atom and radioactive decay. Part 2 is about waves.

Part 1 Nuclear model of the atom and radioactive decay

(a)

Part 2 Waves
Two waves, A and B, are travelling in opposite directions in a tank of water. The graph shows the variation of displacement of the water surface with distance along the wave at a particular instant.

State the amplitude of wave A.

[ 1 ]

5 mm or 5.0 mm ;
units are required Allow other units, eg: $5 / 5.0 \times 10^{-3} \mathrm{~m}$ .

(b)

Wave A has a frequency of 9.0 Hz . Calculate the velocity of wave A .

[ 2 ]

wavelength $=8.0 \mathrm{~cm}$ or 8 cm ;
(accept clear substitution in MP2 for this mark) $v=(f \lambda=) 9 \times 8=72 \mathrm{~cm} \mathrm{~s}^{-1}$ ;
units are required

(c)

Deduce the frequency of wave B.

[ 3 ]

wavelength $=3.9 \mathrm{~cm}$ ;
(accept answers in the range of 3.8 to 4.0 cm )
frequency $=\left(\frac{72}{3.9}=\right) 18$ ;
Hz or $\mathrm{s}^{-1}$ ;

[Maximum number: 4]

This question is in two parts. Part 1 is about a thermistor circuit. Part 2 is about vibrations and waves.
Part 1 Thermistor circuit
The circuit shows a negative temperature coefficient (NTC) thermistor X and a $100 \mathrm{k} \Omega$ fixed resistor R connected across a battery.

The battery has an electromotive force (emf) of 12.0 V and negligible internal resistance.

Part 2 Vibrations and waves

The cone and dust cap D of a loudspeaker L vibrates with a frequency of 1.25 kHz with simple harmonic motion (SHM).

(a)

The sound waves from the loudspeaker travel in air with speed $330 \mathrm{~m} \mathrm{~s}^{-1}$ .

[ 4 ]

(i)

Calculate the wavelength of the sound waves.

[ 1 ]

(ii)

Describe the characteristics of sound waves in air.

[ 3 ]

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Covered syllabus points

Question 1

Question (a)

Question (b)

Question (i)

Question 2

Question (a)

Question (b)

Question (c)

Question 3

Question (a)

Question (i)

Question (ii)