AQA A Level Physics Paper 3 Section A: Practical skills and data analysis June 2022 question paper 7408/3A

Figure 1 shows apparatus used to measure the speed of sound in a steel rod.

The steel rod is suspended from a beam using rubber bands. When the hammer is in contact with the end L of the steel rod, a circuit is completed and the signal generator is connected to the oscilloscope.

Figure 2 shows the waveform then displayed on the oscilloscope.

Which control on the oscilloscope should be used to centre the trace vertically on the screen? Tick (✓) one box.

When the hammer hits end L, a sound wave travels along the steel rod and is reflected at end R. When the wave returns to L the rod bounces away from the hammer and the circuit is broken.

Figure 3 shows the waveform produced by the brief contact between the hammer and L. Note that the waveform has now been centred vertically.

Figure 4 shows the time-base setting of the oscilloscope.

The distance between L and R in Figure 1 is 0.870 m.

Deduce the speed of sound in the steel rod.

A student repeats the experiment using a steel rod of twice the length.

Explain:

• how using the longer rod affects the waveform displayed

• any changes needed to get an accurate result for the speed.

You should include numerical detail.

Figure 5 shows a strip of steel of rectangular cross-section clamped at one end. The strip extends horizontally over the edge of a bench.

A mass m is suspended from the free end of the strip. This produces a vertical displacement y. A student intends to measure y with the aid of a horizontal pin fixed to the free end of the steel strip. She positions a clamped vertical ruler behind the pin, as shown in Figure 6.

Explain a procedure to avoid parallax error when judging the reading indicated by the position of the pin on the ruler. You may add detail to Figure 6 to illustrate your answer.

It can be shown that

where:

L is the distance between the free end of the unloaded strip and the blocks w is the width of the strip and is approximately 1 cm t is the thickness of the strip and is approximately 1 mm E is the Young modulus of the steel.

A student is asked to determine E using the arrangement shown in Figure 5 with the following restrictions:

• only one steel strip of approximate length 30 cm is available

• m must be made using a 50 g mass hanger and up to four additional 50 g slotted masses

• the experimental procedure must involve only one independent variable

• a graphical method must be used to get the result for E.

Explain what the student must do to determine E.

Conductive putty can easily be formed into different shapes to investigate the effect of shape on electrical resistance.

A student uses vernier callipers to measure the diameter d of a uniform cylinder made of the putty.

Suggest one problem with using callipers to make this measurement.

Table 1 shows the calliper measurements made by a student.

Show that the percentage uncertainty in d is about 2.4%. Assume that all the data are valid.

The length of the cylinder is 71 ± 2 mm.

Determine the uncertainty, in mm³, in the volume of the cylinder.

A student is given some putty to form into cylinders.

To find the resistance of a cylinder, metal discs are placed in contact with the ends of the cylinder and connected to a resistance meter.

Figure 7 shows the apparatus.

The student forms the putty into cylinders of different lengths, each of volume

The student plots the graph shown in Figure 8.

Determine ρ. State an appropriate SI unit for your answer.

Figure 8

Figure 9 shows air trapped in a vertical cylinder by a valve and a piston P. The valve remains closed throughout the experiment.

A mass is placed on top of P. P moves downwards and the volume of the trapped air decreases. There are no air leaks and there is no friction between the cylinder and P.

The vertical distance y between the end of P and the closed end of the cylinder is measured. Additional masses are used to find out how y depends on the total mass M placed on top of P. Figure 10 shows a graph of these data.

Show that y is not inversely proportional to M. Use data points from Figure 10.

Figure 10

The masses are removed and the cylinder is inverted. P moves downwards without friction before coming to rest, as shown in Figure 11.

Explain why P does not fall out of the cylinder unless the valve is opened.

The mass of P is 0.350 kg.

Deduce y when the cylinder is in the inverted position shown in Figure 11.

Draw a line of best fit on Figure 10 to arrive at your answer.

Figure 12 shows apparatus used in schools to investigate Boyle’s law.

A fixed mass of air is trapped above some coloured oil inside a glass tube, closed at the top. A pump applies pressure to the oil and the air. The trapped air is compressed and its pressure p is read from the pressure gauge.

A scale, marked in 0.2 cm³ intervals, is used to measure the volume V of the air. A student says that the reading for V shown in Figure 12 is 35.4 cm³.

State:

• the error the student has made

• the correct reading, in cm³, of the volume.

Figure 13 shows data obtained using the apparatus in Figure 12.

Explain why the gradient of the graph in Figure 13 confirms that the air obeys Boyle’s law.

The largest pressure that can be read from the pressure gauge is 3.4 × 10⁵ Pa.

Determine, using Figure 13, the volume V corresponding to this pressure.

State one property of the air that must not change during the experiment. Go on to suggest how this can be achieved.