# Wave properties multiple choice questions

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## Full text

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1. Two identical triangular pulses of amplitude X travel toward each other along a string. At the instant shown on the diagram below, point M is midway between the two pulses.

X

X

M

The amplitude of the disturbance in the string as the pulses move through M is

A. 2X.

B. X.

C. .

2 X

D. 0.

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2. A pulse is sent down a string fixed at one end.

Which one of the following diagrams best represents the reflected pulse?

A .

C .

B .

D .

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3. A plane wave approaches and passes through the boundary between two media. The speed of the wave in medium 1 is greater than that in medium 2. Which one of the following diagrams correctly shows the wavefronts?

A .

C .

B .

D . M e d i u m 1

M e d i u m 1

M e d i u m 1

M e d i u m 1 M e d i u m 2

M e d i u m 2

M e d i u m 2

M e d i u m 2 (1)

4. Which diagram best shows diffraction of plane wavefronts at a single slit?

A .

C .

B .

D .

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5. When a wave crosses the boundary between two media, which one of the following properties of the wave does not change?

A. Amplitude

B. Wavelength

C. Frequency

D. Speed

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6. On which one of the following graphs is the wavelength λ and the amplitude a of a wave correctly represented?

D i s p l a c e m e n t

D i s p l a c e m e n t

D i s p l a c e m e n t

D i s p l a c e m e n t 0 0 0 0 0 0 0 0 a a a a    

D i s t a n c e a l o n g w a v e

D i s t a n c e a l o n g w a v e

D i s t a n c e a l o n g w a v e

D i s t a n c e a l o n g w a v e A .

B .

C .

D .

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Which one of the following diagrams shows the resultant pulse when the two pulses are superposed?

A . B .

C . D .

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8. What change, if any, occurs in the wavelength and frequency of a light wave as it crosses a

boundary from air into glass?

Wavelength Frequency

A. Decreases Decreases

B. Decreases Unchanged

C. Increases Increases

D. Increases Unchanged

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9. The variation with time t of the separate displacements d of a point in a medium due to two

waves is shown below.

+ 2 a

+ a

+ a 0

0 – a

– a – 2 a

d

d

t

t

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the resultant displacement d of the point in the medium?

+ 2 a + 2 a

+ 3 a + 3 a

+ a + a

+ a + a

0 0

0 0

– a – a

– a – a

– 2 a – 2 a

– 3 a – 3 a

d d

d d

t t

t t

A . B .

C . D .

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10. Which of the following diagrams best illustrates the diffraction of waves by an obstacle?

A .

C .

B .

D .

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11. A source S produces sound waves of frequency f and is moving along a straight line as shown below.

I

I I I I I

I V S

Which observer I, II, III or IV could hear a sound of frequency f when the source is in the position shown?

A. I

B. II

C. III

D. IV

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12. The two graphs show the variation with time of the individual displacements of two waves as they pass through the same point.

A

A – A

– A x

– x

1

2 1

2 1

2

0

0 0

0

T

T

t i m e

t i m e d i s p l a c e m e n t

d i s p l a c e m e n t

The displacement of the resultant wave at the point at time T is equal to A. x1 + x2.

B. x1 – x2.

C. A1 + A2.

D. A1 – A2.

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13. A string is stretched between two fixed points. The string is plucked at its centre and is seen to

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Which one of the following expressions gives the frequencies of other possible modes of vibration that have an antinode at the centre? The number n in each expression is an integer.

A. nf

B. (2n – 1)f

C. (n – 1)f

D. (n + 1)f

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14. Sound waves move faster in warm air than in cold air. The diagram below shows plane waves in

cold air moving towards a boundary with warm air.

w a r m a i r

c o l d a i r b o u n d a r y

I

I I

I I I

I V

Which of the arrows shows the possible direction of waves after reaching the boundary?

A. I

B. II

C. III

D. IV

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15. The speed of sound in still air is c. A source of sound moves away from an observer at speed v.

What will be the speed of sound as measured by the observer?

A. c

B. c + v C. c – v D. v – c

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16. The diagram below shows two pulses on a string travelling toward each other.

Which of the following diagrams best shows the shape of the string after the pulses have passed through each other?

A .

B .

C .

D .

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17. Diagram 1 below shows the displacement of part of a medium through which a wave is travelling at time t = 0. Diagram 2 shows the displacement at a later time t = 4.0 s in which the wave has moved forward 10 cm. In this time, the point P on the wave has moved from a crest through zero displacement to a trough.

D i a g r a m 1 D i a g r a m 2

P P

The wavelength of the wave is

A. 5.0 cm.

B. 10 cm.

C. 20 cm.

D. 40 cm.

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18. A source produces water waves of frequency 10 Hz. The graph shows the variation with

horizontal position of the vertical displacement of the surface of water at one instant in time.

## h o r i z o n t a l p o s i t i o n / c m

The speed of the water waves is

A. 0.20 cm s−1.

B. 4.0 cm s−1.

C. 10 cm s−1.

D. 20 cm s−1.

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19. The diagram below shows a transverse wave on a string. The wave is moving from right to left.

X

Y

d i r e c t i o n o f w a v e

u p w a r d s

l e f t r i g h t

d o w n w a r d s

In the position shown, point X has zero displacement and point Y is at a position of maximum displacement. Which one of the following gives the subsequent direction of motion of point X and of point Y?

Point X Point Y

A. left left

B. upwards upwards

C. downwards left

D. downwards upwards

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20. A water surface wave (ripple) is travelling to the right on the surface of a lake. The wave has

period T. The diagram below shows the surface of the lake at a particular instant of time. A piece of cork is floating in the water in the position shown.

Which is the correct position of the cork a time

## T

later?

c o r k

A . B .

C . D .

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21. A wave is travelling through a medium. The diagram shows the variation with time t of the displacement d of a particle of the medium from t = 0 to t = 25 ms.

1 . 5

1

0 . 5

0

– 0 . 5

– 1

– 1 . 5

2 5 2 0

1 5 1 0

5 0

d / c m

t/ m s

Which of the following correctly gives the frequency and the amplitude of the wave?

frequency / Hz amplitude / cm

A. 2.0  10–2 2.0

B. 2.0  10–2 1.0

C. 50 2.0

D. 50 1.0

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22. Which of the following best describes the wave speed of a progressive wave travelling through a

medium?

A. The maximum speed of the vibrating particles of the medium

B. The average speed of the vibrating particles of the medium

C. The speed of the medium through which the wave travels

D. The speed of transfer of energy through the medium

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23. One end of a long string is vibrated at a constant frequency f. A travelling wave of wavelength  and speed v is set up on the string.

The frequency of vibration is doubled but the tension in the string is unchanged. Which of the following shows the wavelength and speed of the new travelling wave?

Wavelength Speed

A.

2 λ

v

B.

2 λ

2v

C. 2

v

D. 2

## 

2v

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24. A string with both ends fixed is made to vibrate in the second harmonic mode as shown by the

dashed lines in the diagram below.

P

Q

The solid line shows a photograph of the string at a particular instant of time. Two points on the string have been marked P and Q.

Which of the following correctly compares both the period of vibration of P and Q and the average speed of P and Q?

Period Average speed

A. same same

B. same different

C. different same

D. different different

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25. The diagram below represents the fundamental (first harmonic) standing wave of sound inside a pipe.

p i p e

P Q

Which of the following correctly represents the displacement of the air at P and Q?

A .

B .

C .

D .

P Q

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26. A transverse travelling wave has amplitude A0 and wavelength λ.

The distance between a crest and its neighbouring trough, measured in the direction of energy transfer of the wave is equal to

A. A0.

B. 2A0.

C. 2

.

D. λ.

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