IB Physics HL C.2 Wave model Questions

SLSL HLHL

Practise IB Physics HL C.2 by reading wave diagrams, using v = fλ with wave data, and explaining how sound and electromagnetic waves propagate.

131 questions in this syllabus scope, with question parts counted together.

Exam points & syllabus

Exam points

Describe a travelling wave as energy or information propagating through oscillations of a medium or fields, with the disturbance moving onward.
Compare particle oscillation with energy propagation: longitudinal motion is parallel, while transverse motion is perpendicular.
Sound in air is a longitudinal travelling disturbance of pressure, forming compressions and rarefactions as energy propagates through the medium.
Compare light’s transverse electric and magnetic fields and vacuum propagation with sound’s longitudinal pressure oscillations and need for a medium.
Read amplitude from equilibrium to an extreme and period between equivalent states with the same direction of motion; include the graph units.
Keep displacement–position and displacement–time graphs separate: obtain wavelength from the former and period from the latter for the same wave.
Use v = fλ = λ/T with consistent units; distinguish a material particle’s changing oscillation speed from the speed of wave propagation.
Convert microseconds or milliseconds before using f = 1/T or counting cycles; 24 full cycles in 6 µs gives 4 MHz.
To find wave speed from two spatial snapshots, measure the shift of a matching feature and divide by elapsed time, respecting the given period limit.
After finding wave speed, read a full spatial wavelength before using f = v/λ, keeping graph-reading and unit tolerances.
In one unchanged medium, use the same wave speed to compare frequencies from different wavelengths rather than assuming their frequencies match.
When a source drives sound in a new medium, retain its frequency and use the speed of that medium to find wavelength.
For light crossing a boundary, connect the speed change and unchanged frequency to the wavelength change through λ = v/f.
Apply the same wave equation to electromagnetic waves; for an infrared frequency of 7 × 10¹² Hz, c/f gives about 4.3 × 10⁻⁵ m.
When wavelength is given and wave speed is known, calculate T = λ/v and round to the number of significant figures explicitly requested.
Show an explicitly requested frequency step before finding wavelength, even when λ = vT could give the same numerical answer.
A separation of one sixth of a wavelength gives a 60° phase difference; use the full wavelength with f when finding wave speed.
Use distance as a fraction of wavelength to shift a particle’s time trace by the corresponding cycle fraction, preserving the period.
For a travelling longitudinal wave, infer particle motion from the changing horizontal displacement, rather than calling a falling graph downward motion.
Find a compression centre where neighbouring particles are displaced towards each other; a downward displacement zero crossing gives that centre.
Explain a rarefaction by neighbouring particles displaced apart: particles on the right displaced right and those on the left displaced left.
For sound in a pipe, an air molecule oscillates back and forth along the pipe axis; a single left or right arrow does not describe its oscillation.
When a prior pipe pattern establishes wavelength, use that wavelength with the source frequency and keep the accepted significant figures.
For a first-harmonic rod coupled to air, equate frequencies and use the stated mode: λrod = 2L and adjacent air displacement nodes are λair/2 apart.
If a permitted depth is specified in wavelengths, turn that limit into a maximum λ and then a minimum f using the stated sound speed.
For travelling-wave energy transfer, distinguish local oscillation from net propagation; an ideal standing wave has no net energy transfer along it.
Describe monochromatic radiation by a single frequency or narrow range of frequencies or wavelengths, rather than the phrase one colour alone.

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: 2]

Outline what is meant by a travelling wave.

[Maximum number: 2]

A spring, such as that in (a), is stretched horizontally and a longitudinal travelling wave is set up in the spring, travelling to the right.

Draw, on the graph in (c)(ii), the displacement of a coil of the spring that is 1.8 cm away from C in the direction of travel of the wave, explaining your answer.

[Maximum number: 2]

A spring, such as that in (a), is stretched horizontally and a longitudinal travelling wave is set up in the spring, travelling to the right.

The graph shows how the displacement x of one coil C of the spring varies with time t.

The speed of the wave is $3.0 \mathrm{~cm} \mathrm{~s}^{-1}$ . Determine the wavelength of the wave.

frequency $=\left(\frac{1}{T}=\frac{1}{0.80}=\right) 1.25 \mathrm{~Hz}$ ;
wavelength $=\frac{v}{f}=\frac{3.0}{1.25}=2.4 \mathrm{~cm}$ or $2.4 \times 10^{-2} \mathrm{~m}$ ;

[Maximum number: 2]

A spring, such as that in (a), is stretched horizontally and a longitudinal travelling wave is set up in the spring, travelling to the right.

Describe, in terms of the propagation of energy, what is meant by a longitudinal travelling wave.

More syllabus points

C.2.5—Mechanical and electromagnetic wave models8 questions

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