hl waves reflect refract answers

7/27/2019 Hl Waves Reflect Refract Answers

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Home learning: Waves - Reflection and refraction

1. Fill out the table below to show the types of waves

Transverse orlongitudinal?

Mechanical orelectromagnetic?

A plucked guitar string transverse mechanical

Radio waves transverse EMSound from a radio longitudinal mechanical

Light from a torch transverse EM

2. Water waves pass by at a rate of one every 7 seconds. Their wavelength is 5metres. Calculate their speed. (hint: calculate their frequency first, then use v=f)frequency = number of waves

time in secondsf = 1 7 = 0.14Hz

v = f = 0.14 * 5 = 0.71 = 0.7 ms -1 (1sf)

3. A wave generator makes 16 waves every 4.0 seconds. These 16 waves cover adistance of 16cm.a) Calculate the frequency of the waves.frequency = number of waves

time in secondsf = 16 4.0 = 4.0Hzb) Calculate the period of the waves.

T = 1f

T = 1 4.0 = 0.25 s (2sf)c) Calculate the wavelength of the waves.16 waves cover 16cm, so 1 wave (which is one wavelength) covers 1.0cmd) Calculate the speed of the waves.v = f = 4.0 * 0.01 = 0.040 ms -1 (2sf)

4. Complete the diagram below to show how the waves are reflected from the

boundary.

a) Label your diagram to show thedirection of travel of thereflected waves.b) Label the angle of incidenceand angle of reflection.

angle of

reflection

angle ofincidence


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5. The diagram shows waves arriving at a boundary between deep and shallow water.In the deep region a total of 10 waves are counted passing by in 4.0s. Theirwavelength is 3.0cm in the deep water and 2.0cm in the shallow water.

a) Calculate the frequency of the waves in thedeep region.frequency = number of waves

time in secondsf = 10 4.0 = 2.5Hz (2sf)b) What is the frequency of the waves in theshallow region?2.5Hz (the frequency of the waves does notchange from deep to shallow water, only the

wavelength and speed change).c) Calculate the wave speed in the shallow region.v = f = 2.5 * 0.020 = 0.050 ms-1 (2sf)

6. The diagram shows a ripple tank set up to demonstrate refraction. As the wavestravel from the deep region into the shallow region they refract and changedirection.

a) Draw the pattern showing the wave fronts as they pass into the shallow region.b) Each incident wave takes 0.20s to travel the 15cm shown. Calculate the speed ofthe waves.v = d

tv = 0.15 0.20 = 0.75 ms-1 (2sf)c) Use the diagram to work out the wavelength of the incident waves.3 waves cover 15cm (remember to count complete wavelengths, not number ofcrests). So 1 wave covers 5cm. The wavelength is 5.0cm (2sf)d) Calculate the frequency of the incident waves.f = v

f = 0.75 0.050 = 15Hz (2sf)e) What is the frequency of the refracted waves?15Hz (the frequency of the waves does not change from deep to shallow water, onlythe wavelength and speed change).

DEEP

SHALLOW

15cm

DEEP SHALLOW

direction of propagation


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f) The wavelength of the refracted waves is measured to be 4.0cm. Use v=f tocalculate the speed of the waves in the shallow region.v = f = 15 * 0.040 = 0.60 ms-1 (2sf)g) Use your values to verify that v1/v2 = 1/2v1/v2 = 0.75 0.60 = 1.251/2 = 0.05 0.04 = 1.25Both are equal to 1.25, so v1/v2 = 1/2 is proven to be true.

7. The diagram below shows a wave generator producing waves with a frequency of 20Hz. The wave fronts are incident on a plane boundary which separates a shallowregion from a deep region. at an angle of 30. The speed of the waves in the shallowregion is 40 cm s-1 and in the deep region is 55 cm s-1.

a) Calculate the angle of refraction in the deep region.(Use vdeep/vshallow = sin deep/sinshallow)

vdeep = 55 cm s-1vshallow = 40 cm s

-1

deep = ?shallow = 30

55 = sin deep40 sin30

sin30 x 55 = sin deep

40

sin-1( sin30 x 55 ) = deep40

deep = 43 (2sf)

DEEP

SHALLOW

30

hl waves reflect refract answers

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