Kalaafaanu School KALAAFAANU SCHOOL DEPARTMENT OF PHYSICS WORKSHEET- WAVES & SOUND GRADE-09 Name: ----------------------Index: --------------Reg.:------------Class: ---------

Grade -9 / Physics

1. A wave travels along a stretched spring. Fig. 3.1 shows the appearance of the spring at one instant.

(a) (i) On Fig. 3.1, label one compression. (ii) Describe what is meant by a compression. (iii) Sound waves also contain compressions and rarefactions. Give one other similarity between the motion of particles in a sound wave and the motion of coils in the stretched spring. ] (b) Fig. 3.1 is drawn full scale. (i) (ii) Measure the wavelength of the wave travelling along the spring. Determine the frequency of the wave, given that the speed of the wave is 75 cm/s. State clearly the formula that you use and give your answer to a suitable number of significant figures.

2. (a) Fig. 6.1 shows the position of layers of air, at one moment, as a sound wave of constant frequency passes through the air. Compressions are labelled C. Rarefactions are labelled R.

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Kalaafaanu School (i) State how Fig. 6.1 would change if 1. the sound had a higher frequency, 2. the sound were louder. (ii)

Grade -9 / Physics

On Fig. 6.1, draw a line marked with arrows at each end to show the wavelength of the sound.

3. Fig. 8.1 shows a loudspeaker cone oscillating to produce sound waves.

(a) As the sound wave passes a point, it produces regions of higher and lower pressure. State the names of these regions. higher pressure .......................................................... lower pressure .......................................................... (b) Describe how the movement of the loudspeaker cone produces these regions of different pressure. I. II. higher pressure lower pressure

(c) State the effect on the loudness and pitch of the sound from the loudspeaker when (i) the amplitude increases but the frequency of the sound stays the same,

(ii) I. II.

I. loudness II. pitch the amplitude stays the same but the frequency increases. loudness pitch

4. A disused railway line has a length of 300 m. A man puts his ear against one end of the rail and another man hits the other end with a metal hammer, as shown in Fig. 7.1.

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Kalaafaanu School

Grade -9 / Physics

(a) (i) State an approximate value for the speed of sound in air. (iii) Sound travels at 5000 m / s in steel. Calculate the time it takes for the sound to travel along the rail.

(b) The man with his ear to the railway line actually hears two sounds from the hammer, separated by a short interval. Explain why he hears two sounds. 5. A tsunami is a giant water wave. It may be caused by an earthquake below the ocean. Waves from a certain tsunami have a wavelength of 1.9 105 m and a speed of 240m/s. Calculate the frequency of the tsunami waves.

6. On the below figure shows a machine for making loud sounds. It is called a siren. This consists of a rotating disc with 25 holes. As each hole passes the jet, a puff of air passes through the hole.

(i) How many puffs of air will there be during one revolution of the disc? (ii) The disc rotates 40 times per second. Show that the frequency of the note produced by the siren is 1000 Hz. (b) The siren described in (a) is located some distance from a large building The siren is briefly sounded once. A short time later, the sound is heard again. KS/Grade-8/ Dept of Physics/Worksheet on waves and sound Page 3

Kalaafaanu School

Grade -9 / Physics

(i) Why is this second sound heard? (ii) What is the frequency of this second sound? (iii) What is the amplitude of this second sound? 7. Observations of a distant thunderstorm are made. (a) During a lightning flash, the average wavelength of the light emitted is 5 10 light travels at 3 10 m/s. Calculate the average frequency of this light.87

m. This

(b) The interval between the lightning flash being seen and the thunder being heard is 3.6 s. The speed of sound in air is 340 m/s. (i) (ii) Calculate the distance between the thunderstorm and the observer. Explain why the speed of light is not taken into account in this calculation.

8. (a) The below figure shows the air pressure variation along a sound wave.

(i) On AB of the above figure, mark one point of compression with a dot and the letter C and the next point of rarefaction with a dot and the letter R. (ii) In terms of the wavelength, what is the distance along the wave between a compression and the next rarefaction? (b) A sound wave travels through air at a speed of 340 m/s. Calculate the frequency of a sound wave of wavelength 1.3 m.

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Kalaafaanu School

Grade -9 / Physics

9. A girl is walking along a path 1600m from the rock-face of a quarry (a place where stone is obtained).

(a) The quarry workers set off an explosion at X to break up some rock. The girl measures the time interval between seeing the flash and hearing the bang. The time is 5.0 s. (i) Calculate the speed of the sound. (ii) State what assumption you have made in your working in (i). (b) Suppose the explosion had taken place at Y instead of X. State two ways in which the girls observations would have been different.

10. A student sits in the middle of a large rectangular hall which is 17m wide. When the student bangs a drum, two echoes are heard, 50 ms and 80ms, respectively, after the bang. Assuming that there is no echo from the ceiling, calculate (a) the speed of sound in air, (b) the length of the hall. The speed of light in air is 3.00 x 10 6 m/s. The speed of sound in air is 0.340 Km/s. An observer is 5.00 km away from a lightning discharge. (c) Calculate the travel time, to the observer, of (i) light from the lightning flash, (ii) sound from the thunder. (d) what is the time interval between the observer seeing the lightning and hearing the thunder?

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Kalaafaanu School

Grade -9 / Physics

11. A student measures the speed of sound in a laboratory, as shown in the below figure.

The sound is received by two microphones placed a distance d apart. The time interval t between the sound arriving at the two microphones is recorded. (a) (i) Explain how sound travels through the air to the microphones. (ii) Explain why microphone 2 detects a quieter sound than microphone 1. (b) Fig. 11.2 shows average values for t as d is varied.

(i) Draw a distance-time graph from the results given from the above table. (ii) Using your graph, calculate the speed of sound in air.

12. Fig. 4.1 shows circular wavefronts produced at the centre of a circular ripple tank.

Two corks, A and B, float on the water in the ripple tank. They move up and down on the surface of the water as the wave passes. The wavelength of the wave is 8.0 cm.

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Kalaafaanu School Fig. 4.2 shows how the displacement of A varies with time.

Grade -9 / Physics

(a) State the amplitude of the vibrations of A as the wave passes. (b) The horizontal distance between A and B is half the wavelength of the wave. On Fig. 4.2, sketch a graph to show how the displacement of B varies with time. (c) (i) Use Fig. 4.2 to determine the frequency of the wave. (ii) The distance between the centre of the ripple tank and its edge is 40 cm. Determine the time taken by a wavefront to travel from the centre of the tank to the edge.

13. Fig. 4.1 and Fig.4.2 are diagrams of a ripple tank being used to show two properties of waves. (a) Fig. 4.1 shows wavefronts approaching a barrier in the water.

Complete Fig. 4.1 to show the reflection of the wavefronts at the barrier.

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Grade -9 / Physics

(b) Fig. 4.2 shows the wavefronts approaching shallow water above a piece of glass.

(i) (ii)

Complete Fig. 4.2 to show the wavefronts in the shallow water. As the wave passes into the shallow water, state what, if anything, happens to

1. the wave speed, .............................................................................................. 2. the frequency. .................................................................................................. 14. a) Describe a method for measuring the speed of sound in air. In your account, state clearly how the sound is made, what measurements are taken, how the result is calculated, one precaution to produce an accurate result. (b) Ultrasound is used in quality control to detect cracks in metal. Pulses of ultrasound are sent into the metal from a transmitter. A detector is placed next to the transmitter on the front surface of the metal. Fig. 10.1 shows the oscilloscope trace of the ultrasound pulses produced if the metal contains no cracks.

One division along the x-axis represents 1.0 10-6 s. Pulses labelled S are the pulses initially sent out from the transmitter. Each pulse labelled R is the reflection from the back surface of the metal of the previous pulse S. KS/Grade-8/ Dept of Physics/Worksheet on waves and sound Page 8

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Grade -9 / Physics

(i) . (ii)

State what is meant by ultrasound. Use Fig. 10.1 to calculate the number of pulses sent out by the source in one second. Suggest two reasons why the amplitude of R is less than the amplitude of S. Some time later, the piece of metal is tested again. It now has a small Crack half-way between the front surface and the back surface.

(iii) (iv)

On Fig. 10.1, draw the position and size of the pulses produced by this crack. Label each of these pulses C. (v) A second beam of ultrasound has a frequency of 8.0 106 Hz and a speed of 4000 m / s in the metal.

Calculate the wavelength of this ultrasound in the metal. 15. (a) Ripple tanks may be used to produce plane water waves. Draw a labelled diagram of a ripple ank used to produce plane water waves. Your diagram should show how the waves are made and how they are observed. (b) Water waves may be refracted at a boundary. Fig.11.1 shows four wavefronts of a water wave incident on a boundary. As the wave crosses the boundary, the wave is refracted. (i) Copy Fig.11.1 and draw the wavefronts after refraction, to the right of the boundary.

(ii) Describe how the ripple tank in (a) could be used to produce this refraction.

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Kalaafaanu School

Grade -9 / Physics

(iii) State why the water waves are refracted. (c) Water waves may be refracted at a boundary. Fig.11.1 shows four wavefronts of a water wave incident on a boundary. As the wave crosses the boundary, the wave is refracted. (i) Copy Fig.11.1 and draw the wavefronts after refraction, to the right of the boundary. (ii) Describe how the ripple tank in (a) could be used to produce this refraction. (iii) State why the water waves are refracted. (d) The wavefronts shown in Fig. 11.1 are drawn full-scale. It takes 0.75 s for a wavefront to travel from A to D. Using measurements taken from Fig.11.1, determine, for this wave, (i) the speed, (ii) the wavelength, (iii) the frequency.

16. During a thunderstorm, thunder and lightning are produced at the same time. (a) A person is some distance away from the storm. Explain why the person sees the lightning before hearing the thunder. A scientist in a laboratory made the following measurements during a thunderstorm.

time from start of storm / minutes time between seeing lightning and hearing thunder /s (i)

0.0 3.6

2.0 2.4

4.0 1.6

6.0 2.4

8.0 3.5

10.0 4.4

How many minutes after the storm started did it reach its closest point to the laboratory? How can you tell that the storm was never immediately over the laboratory? When the storm started, it was immediately above a village 1200 m from the laboratory. Using this information and information from Fig. 7.1, calculate the speed of sound.

(ii) (iii)

(iv)

State the assumption you made when you calculated your answer to (b)(iii).

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Kalaafaanu School

Grade -9 / Physics

17. Some plane waves travel on the surface of water in a tank. They pass from a region of deep water into a region of shallow water. Fig. 6.1 shows what the waves look like from above.

(a) State what happens at the boundary, if anything, to (i) (ii) (iii) the frequency of the waves, the speed of the waves, the wavelength of the waves.

(b) The waves have a speed of 0.12 m / s in the deep water. Wave crests are 0.08 m apart in the deep water. Calculate the frequency of the source producing the waves. State the equation that you use. Fig. 6.2 shows identical waves moving towards the boundary at an angle.

On Fig. 6.2, draw carefully the remainder of waves A and B, plus the two previous waves which reached the shallow water. You will need to use your ruler to do this.

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