Interference & Stationary Waves (Edexcel International A Level Physics)

Topic Questions

2 marks

In an experiment to determine the speed of sound in air, a student held a vibrating tuning fork above a glass tube. The air column in the tube could be adjusted by raising or lowering the tube into a cylinder containing water. When the length of the air column was $l$ , a stationary wave with one node and one antinode was produced as shown.
This caused a sound to be heard.

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Explain how the stationary wave was formed in this experiment.

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5 marks

A sound was heard when $l$ was 19.3 cm.

Determine a value for the speed of sound in air.

frequency of tuning fork = 440 Hz

(3)

Speed of sound in air = .......................................................

ii)

The antinode is slightly further from the water than the end of the glass tube.

Explain how this would affect the accuracy of your calculated value for the speed of sound.

(2)

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3 marks

A student investigated the reflection of microwaves from a metal plate and a glass plate.

The metal plate reflects microwaves and the glass plate partially reflects microwaves.

A plan view of the apparatus is shown.

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The metal plate, the transmitter and the receiver were kept in fixed positions.

The value of d was varied by moving the glass plate.

As d varied, the intensity of the microwaves detected by the receiver varied.

Explain why.

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5 marks

The student recorded values of d when the receiver showed a maximum value of intensity.
He recorded d for a sequence of five maxima.

Maxima	1	2	3	4	5
d / cm	9.9	11.1	12.7	13.9	15.4

Determine the wavelength of the microwaves being transmitted.

(3)

Wavelength = ..........................................

ii)

Calculate the frequency of the microwaves being transmitted.

(2)

Frequency = ...........................................

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1 mark

A student investigated stationary waves on a string, using the apparatus shown.

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The frequency f of the vibrator was adjusted until a stationary wave was formed with a node at each end. This was repeated for various stationary waves on the string. A metre rule was used to measure the distance d between adjacent nodes on the string.

The resolution of the metre rule was 1 mm, but the measurements were recorded to the nearest 0.5 cm.

Suggest why.

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7 marks

The student plotted a graph of d against 1/f as shown.

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Determine the total mass of the hanging masses used in the investigation. Mass per unit length of string = 4.5 × 10^–4 kg m^–1

(5)

Total mass of hanging masses = ............................

ii)

The string was replaced with one that had twice the mass per unit length.

The length of the string and the mass of the hanging masses did not change.

Add a line to the graph to show how d varied with 1/f for the new string.

(2)

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