AQA A Level Physics Paper 3 June 2025 question paper 7408/3

This question is based on an investigation into how the frequency of the first-harmonic stationary wave on a string varies with tension (required practical activity 1).

Figure 1 shows the arrangement for this investigation.

The tension in the string is equal to the weight mg of the total mass m tied to the string.

The frequency is changed until the first-harmonic stationary wave appears on the string. This frequency f is determined using the oscilloscope.

The process is repeated for different values of m.

Identify two control variables for the arrangement shown in Figure 1.

You may annotate Figure 1 as part of your answer.

The total mass m is made from a mass hanger and up to three slotted masses.

One 20 g, one 50 g and one 100 g slotted mass are provided. The hanger has a mass of 100 g.

The hanger must not be removed from the string.

Which statement is correct?

Tick (✓) one box.

The frequency f is calculated using the waveform displayed on the oscilloscope. Figure 2 shows the waveforms displayed on the oscilloscope when m = 100 g and when m = 200 g.

m = 100 g m = 200 g

The y-voltage gain setting is 5 V div⁻¹. The time-base setting is 20 ms div⁻¹.

Determine V_rms, the root mean square voltage of the ac supply.

Determine the period of the waveform on Figure 2 when m = 100 g.

Deduce whether Figure 2 shows the expected result of doubling m from 100 g to 200 g.

Figure 3 shows a circuit that causes a loudspeaker to emit ‘clicks’ at a constant rate. The time T between successive clicks depends on the resistances R₁ and R₂ and the capacitance C. You do not need to know any details about the electronic system.

A student uses a stopwatch to determine T. Table 1 shows the student’s repeated measurements of 20 T.

Suggest why the student measures 20 T.

Suggest why the student repeats their measurements of 20 T.

Determine the percentage uncertainty in the student’s result for T. Assume that all the data in Table 1 are valid.

The student determines T for different values of R₂. The values of R₁ and C are not changed.

The student produces the graph in Figure 4.

It can be shown that

The student has access to a range of fixed and variable resistors. The student wants to modify the circuit in Figure 3 so that T can be varied continuously from a minimum of 0.70 s to a maximum of 1.25 s.

Show how the student can achieve this by combining two resistors to make R₂. You should use information from Figure 4.

Figure 5 shows apparatus to investigate how the resistance R of a lamp filament varies with the absolute temperature T of the filament.

The lamp is inside an oven.

The oven temperature is increased to a steady value. The filament is at the same temperature as the inside of the oven.

The temperature T in kelvin is determined using the thermometer. An ohm-meter is connected to the filament to determine R at temperature T.

The oven temperature is increased to new steady values and further readings of T and R are recorded.

Figure 6 shows the variation of R with T.

It can be shown that:

where:

R₀ is the resistance of the filament at temperature T₀ α is a constant.

Determine α using the graph in Figure 6. State an appropriate SI unit for your answer.

In a different investigation, a student investigates how the electrical power P transferred in the same filament lamp varies for values of T greater than 800 K.

The student assumes that α is constant for all values of T.

Figure 7 shows the circuit that the student uses. The temperature of the filament is controlled by the energy supplied to it from the battery.

Complete Table 2.

It can be shown that P₁ Tⁿ where n is an integer.

Determine n.

In your answer you should:

• use Table 3 to organise the data you will plot

• plot a suitable graph on Figure 9.

This question is about the vertical oscillations of a test tube in a liquid.

Figure 10 shows some wire wound tightly around a test tube. The ends of the wire are secured with tape.

P and Q are points marked on the wire, as shown in the enlarged view in Figure 10. A travelling microscope with a vernier scale is used to measure the distance between P and Q. The microscope reading at P is 9.26 mm.

Figure 11 shows the microscope reading at Q.

Show that the wire has a thickness of approximately 1.2 mm.

The external diameter of the test tube is 18.0 mm.

Deduce the length of wire between P and Q.

A student investigates vertical oscillations of the test tube in a liquid.

Figure 12 shows the test tube and wire floating at rest in a beaker of dark-coloured oil. The part of the test tube below the surface cannot be seen clearly through the oil.

The test tube is then pushed downwards as far as possible, as shown in Figure 13.

The test tube is now released from the position shown in Figure 13. The test tube oscillates vertically with simple harmonic motion of period T.

A horizontal fiducial mark is used to reduce uncertainty in the measurement of T. The fiducial mark is to be placed level with one of the positions A, B, C or D shown in Figures 12 and 13.

Identify the correct position for the fiducial mark. Go on to explain why you chose this position.

When the total mass of the test tube, wire and tape is constant, it can be shown that:

When the test tube oscillates in the oil, T is 0.587 s.

The test tube is cleaned and placed in an identical beaker containing milk. When the test tube oscillates in the milk, T is 0.534 s.

Determine the density of the milk.

Due to damping, only a small number of oscillations occurs after the test tube is released.

The student wants to produce a greater number of oscillations for a particular liquid without changing T.

State and explain two ways in which the apparatus can be modified to achieve this.