Light and Sound
5 marks · NormalSound and light both travel as waves but have different properties.
State whether light and sound are transverse or longitudinal waves respectively. Give one piece of evidence for your answer in each case.
A sound wave has a frequency of 440 Hz and travels at 340 m/s in air. Calculate its wavelength.
State the range of frequencies the average person can hear. Describe how loudness and pitch are represented on an oscilloscope trace of a sound wave.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
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(a) — · must show light: transverse; sound: longitudinal; evidence for each (e.g., polarisation for light, needs medium for sound)
(b) 0.77 m · must show use v = f × λ
(c) — · must show audible range: 20 Hz to 20 000 Hz; loudness = amplitude; pitch = frequency on oscilloscope
Must show: Both types stated; clear evidence; correct calculation; correct description of frequency and amplitude
Common mistakes: Mixing up wave types; incorrect calculation formula
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States light is transverse and sound is longitudinal.
B1 (a) · 1 mark · Provides correct evidence for each type (e.g., polarisation for light, needs medium for sound).
M1 (b) · 1 mark · Uses correct formula λ = v/f. (follow-through)
A1 (b) · 1 mark · Correct answer 0.77 m. (follow-through)
B1 (c) · 1 mark · States correct audible range; matches amplitude and frequency to loudness and pitch on oscilloscope.
Worked solution
a) Light waves are transverse because they oscillate perpendicular to direction of energy transfer and can be polarised. Sound waves are longitudinal because oscillations are parallel to the direction of travel and require a medium.
c) The human audible range is 20 Hz to 20 000 Hz. Loudness is shown by amplitude (height of trace); pitch is shown by frequency (number of waves per second) on an oscilloscope trace.