AQA A Level Physics Paper 3 Section A: Practical skills and data analysis June 2017 question paper 7408/3A

A microwave transmitter T and a receiver R are arranged on a line marked on the bench.

A metal sheet M is placed on the marked line perpendicular to the bench surface.

Figure 1 shows side and plan views of the arrangement. The circuit connected to T and the ammeter connected to R are only shown in the plan view.

The distance y between T and R is recorded.

T is switched on and the output from T is adjusted so a reading is produced on the ammeter as shown in Figure 2.

M is kept parallel to the marked line and moved slowly away as shown in Figure 3

The reading decreases to a minimum reading which is not zero. The perpendicular distance x between the marked line and M is recorded.

The ammeter reading depends on the superposition of waves travelling directly to R and other waves that reach R after reflection from M.

State the phase difference between the sets of waves superposing at R when the ammeter reading is a minimum. Give a suitable unit with your answer.

Explain why the minimum reading is not zero when the distance x is measured.

When M is moved further away the reading increases to a maximum then decreases to a minimum.

At the first minimum position, a student labels the minimum n = 1 and records the value of x. The next minimum position is labelled n = 2 and the new value of x is recorded. Several positions of maxima and minima are produced.

Describe a procedure that the student could use to make sure that M is parallel to the marked line before measuring each value of x. You may wish to include a sketch with your answer.

It can be shown that

The student plots the graph shown in Figure 4.

and adds error bars to the graph.

Determine

the maximum gradient G_max of a line that passes through all the error bars

the minimum gradient G_min of a line that passes through all the error bars.

Explain how the graph in Figure 4 can be used to obtain the value of y. You are not required to determine y.

Suppose that the data for n = 13 had not been plotted on Figure 4.

Add a tick () in each row of Table 1 to identify the effect, if any, on the results

The Y-voltage gain and time-base settings of the oscilloscope are shown in Figure 6.

When switch S is open (off) the oscilloscope displays the waveform shown in Figure 7.

When S is closed (on) the oscilloscope displays the waveform shown in Figure 8.

Determine the peak-to-peak voltage V of the waveform shown in Figure 8.

Determine the frequency f of the waveform shown in Figure 8.

Figure 9 shows the signal generator connected in series with a resistor R and a capacitor C.

The oscilloscope is connected across the capacitor. The Y-voltage gain and time-base settings are still the same as shown in Figure 6.

When S is closed (on) the oscilloscope displays the waveform shown in Figure 10.

Determine the time constant of the circuit in Figure 9.

A student suggests that setting the time-base to 0.2 ms division might reduce uncertainty in the determination of the time constant.

State and explain any possible advantage or disadvantage in making this suggested adjustment.

The student connects an identical resistor in parallel with R and uses the oscilloscope to display the waveform across C.

Draw on Figure 11 the waveform you expect the student to see.

The waveform of Figure 10 is shown as a dashed line to help you show how the waveform changes.

Explain the change in the waveform.

Figure 12a is a graph of voltage against time showing the output of the signal generator. Figure 12b shows the voltage across C during the same time interval. The student interchanges the positions of R and C and connects the oscilloscope across R. Complete Figure 12c to draw the voltage across R during the time interval.

State and explain what changes, if any, the student needs to make to the settings of the oscilloscope so the waveform across R is fully displayed.

A block is used to raise one end of the track. A bumper fitted with a rubber cord is attached at the lower end of the track. The air track has a length of 2 m and there is a scale with major divisions marked in centimetres along the side; the zero of the scale is at the lower end, as shown in Figure 13.

A glider is placed in contact with the rubber cord on the bumper at the lower end of the track. The position of the glider relative to the fixed scale can be determined using Figure 14.

The glider is then moved to the position shown in Figure 15.

Figure 15

The air supply to the track is turned on and the glider is released. The glider accelerates down the track, strikes the rubber cord on the bumper and rebounds back up the track. The glider is allowed to bounce off the rubber band 20 times before it is stopped.

A student reads and records the highest position p of the glider after each rebound n. Some of the student’s data are shown in Table 2. Additional columns have been provided to allow you to complete question 03.2 and question 03.3.

The value of p corresponding to n = 0 is the glider’s initial position at the top of the track.

Deduce this value of p using Figure 13 and Figure 15. Write this result in Table 2.

As it travels from the lower end of the track to each position p the glider moves through a distance x.

Deduce x for all the values of n using Figure 14. Write these results in Table 2.

Plot on Figure 16 a graph of ln (x /cm) against n.

Record your values of ln (x /cm) in Table 2.

Explain why the graph you plotted confirms that x decreases exponentially with n.

Figure 16

Determine, using your graph in Figure 16, the value of x when n is 20.

Describe and explain two procedures the student should take to reduce uncertainty in the measurements of p.