Interference & Stationary Waves (Edexcel International A Level Physics)

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

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.

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

i) 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

Total mass of hanging masses = ............................(5)

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)

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.

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.

The student recorded values of d when the receiver showed a maximum value of intensity.

He recorded d for a sequence of five maxima.

i) Determine the wavelength of the microwaves being transmitted.

Wavelength = .......................................... (3)

ii) Calculate the frequency of the microwaves being transmitted. Frequency = ...........................................(2)