Suggested solutions for Worksheet on waves

Chapter 13
MCQ
 1. D (fact)
 2 B (direction of vibration and wave
motion is parallel, compression and
rarefaction can be seen – longitudinal
wave)
 3 C (Draw the wave for the next instance,
compare the positions)
MCQ
 4 B (speed = frequency x wavelength)
5 D
6 C
Section B
 1a) Transverse wave
 1b) Transverse wave travel perpendicular to
the direction of vibration, whereas
longitudinal waves travel parallel to the
direction of vibration
 1c) Both types of waves transfer energy from
one point to another without physically
transferring the medium the waves travel in.
Section B
 1d) Transverse waves: light waves
 Longitudinal waves: sound waves
 2a) The wavelength of a wave is the shortest
distance between any two points on the
wave that are in phase.
 The amplitude of a wave is the maximum
displacement of a point on the wave from its
rest position.
Section B
 2c) Speed = 0.83 m/s, wavelength = 0.2 m
 Frequency = speed/wavelength = 4.2 Hz
3ai) The period of a wave is the time taken to
produce one complete wave.
3aii) Time taken to travel half a wavelength =
2s.
Period of wave T = time taken to travel one
wavelength = 4s
Section B
 3b) Since the wave travels half a
wavelength (4m) in 2 s,
 Speed = distance / time = 4/2 =2 m/s
 4a) 30 cm
 4b) 4 m
 4ci) frequency = 1/T = 2.0 Hz
Section B
 4cii) The particle moves down past the
rest position until it reaches maximum
displacement in the negative direction. It
then moves up and reaches the rest
position at t = 0.375s.
(explanation: the period of the wave is 0.5
s. After 0.375 s, the wave would have
moved ¾ cycle)
 4ciii) At t=3.25s, the particle would have
oscillated for 6.5 more complete
oscillations. (3.25/0.5). Hence, the
particle is half a cycle out of phase, it will
be at -30 cm.
 5a)
2
 5b)iii)
4
Section B
 5bi) Frequency = speed/wavelength =
0.4/(0.02) = 20 Hz
 5bii) Period = 1 /f = 1/20 = 0.05 s
Section C
 1ai) Speed
 = frequency x wavelength
 = 2 x 0.5 = 1cm/s
 1aii) wavelength
 = speed/frequency
 1/ 2.5 = 0.4 cm
Section C
 2ai) A wavefront is an imaginary line on a
wave that joins all adjacent points that
are in phase.
 2aii) A bright zone indicates a set of
waves near a crest. A dark zone indicates
the a set of wavefronts near a trough.
 2bi) 4 2bii) 10
Section C
 2c) Region A,
 speed = frequency x wavelength
 =2 x 5.5 = 11.0 mm/s
 Region B,
 speed = frequency x wavelength
 =2 x 2 = 4.0 mm/s
Section C
 2d) As the waves move from region A to
region B, their wavelength shortens from
5.5 mm to 2.0 mm. According to the
formula v = f x λ, their speed decreases
from 11mm/s to 4m/s. Their frequency
remains unchanged as the frequency of
the dipper does not change.
Data Based Question
 3ai) Point E and M
 3aii) Point A, I and Q.
 3b) Amplitude = (6.6 – 6.2)/2 =0.2m
 3ci) Frequency = 1/T = ¼ = 0.25 Hz.
 3cii) Wavelength = distance between 2
consecutive points that are in phase
(between the 2 trough) = 8m.
Data Based Question
 3ciii) Speed = 0.25 x 6 = 1.5m/s.
 3d) Transverse wave.