AQA A Level Physics Paper 3 Section A: Practical skills and data analysis June 2023 question paper 7408/3A

A stroboscope emits bright flashes of white light. The duration of each flash and the frequency of the flashes can be varied.

Table 1 shows information about the stroboscope.

The duration of each flash is T₁. The time from the start of a flash to the start of the next flash is T₂.

The duty cycle of a stroboscope is defined as .

What is the maximum duty cycle of the stroboscope?

Tick () one box.

Figure 1 shows images produced in an experiment in which a bouncing ball is illuminated by a stroboscope. The stroboscope flashes at a constant frequency.

Suggest why T₁ must be very short for this experiment.

Figure 2 shows the first six images starting with n = 0, where n is the image number.

The images are used to determine: H, the vertical distance from the bottom of the ball to the floor when n = 0 h, the vertical distance from the bottom of the ball to the floor for each non-zero value of n.

The n = N image is produced at the instant that the ball hits the floor for the first time. For n between 0 and N it can be shown that

where u₀ is the vertical velocity of the ball when n = 0 g is the acceleration due to gravity f is the frequency of the flashes.

In order to find g, a graph is plotted with values of on the y

Suggest what is plotted on the x-axis. Go on to explain how g is determined from this graph.

The following data are recorded.

H = 1550 mm f = 31.0 Hz

The graphical analysis of data from Figure 1 gives g as 9.79 m s⁻².

Determine u₀.

Figure 3 shows positions of the bottom of the ball for n = 40 to n = 66 In this range of positions, the ball makes contact with the floor for the second and third times. Values of h, the vertical distance from the bottom of the ball to the floor, are plotted on the y-axis. Values of s, the horizontal displacement from a point on the floor below the centre of the n = 0 image, are plotted on the x-axis.

Determine, in mm s⁻¹, the horizontal velocity of the ball between the second and third contacts of the ball with the floor.

Determine the time between the second and third contacts. Annotate Figure 3 to show your method.

Figure 4 is a plot of current – voltage data for a filament lamp L.

Figure 4

The current I was measured as the voltage V across L was increased at a steady rate. These data were obtained using a current sensor and a voltage sensor connected to a data logger. The logger recorded data at a rate of 2.5 Hz.

Determine, in V s⁻¹, the rate of increase of V.

State two advantages of using data logging for this experiment.

Figure 5 shows two circuits that can be used to collect current–voltage data.

The dc supply has an emf of 12 V and negligible internal resistance. The current sensor and the voltage sensor behave as ideal meters.

In circuit 1:

• X is used as a variable resistor with a maximum resistance of 14.9 Ω

• when X is set to maximum resistance, the resistance of L is 2.3 Ω.

In circuit 2, X is used as a potential divider.

Discuss, with reference to circuit 1 and circuit 2, whether either circuit can produce all the data shown in Figure 4. Support your answer with a calculation.

Table 2 shows some values of V that are plotted on Figure 4 and corresponding results for I and for the power P dissipated in L.

Complete Table 2.

Plot on Figure 6 a graph of P against V. You should use only the data in your completed Table 2.

L is connected to a 12 V power supply of negligible internal resistance. L then dissipates its rated power P_r.

A second lamp, identical to L, is now connected in series with L.

Determine the percentage of P_r that is dissipated in this circuit.

Figure 7a shows the front view of a vertical coil mounted on a circular frame.

Figure 7b is a side view showing a section through the frame and coil. A constant direct current in the coil produces magnetic flux represented by the magnetic field lines on this diagram.

Figure 7a Figure 7b

Point Q is at the centre of the coil. A sensor placed at Q detects B_H, the horizontal component of the magnetic flux density. The effect of the Earth’s magnetic field at Q is negligible.

Discuss whether a search coil is a suitable sensor to detect B_H.

B_H is measured at Q with the coil vertical.

The coil is now rotated about Q through 25° as shown in Figure 8. The current in the coil does not change.

A new measurement of B_H is made with the coil fixed in this new position.

Determine the percentage change in B_H produced by this rotation of the coil. Show your working.

Figure 9 shows a protractor being used to measure the angle through which the coil is rotated.

Estimate the percentage uncertainty in this result. Justify your answer.

Figure 10 shows an arrangement of two vertical coils. Four experiments are done using this arrangement.

Coil 1 and coil 2 are identical and have a radius r. The coils are separated by a distance r and have a common axis PR. Q is at the centre of coil 1.

The four different experiments investigate how B_H varies with x, the displacement of the sensor from Q along PR.

In experiment 1, the current in coil 1 is 225 mA and the current in coil 2 is zero.

In experiment 2, the current in coil 1 is zero and the current in coil 2 is 225 mA.

Figure 11 shows the results of experiment 1 and experiment 2.

During experiment 1, B_H is measured with the sensor at Q. The sensor is then moved along PR until the value of B_H is halved. The distance from Q to the sensor is x_0.5

In experiment 3, the current in both coils is 225 mA so that the magnetic fields produced by coil 1 and coil 2 are combined.

The resultant B_H has a constant maximum value in the region between x = and

Deduce, in mT, the value of B_H in this region.

State two characteristics of the magnetic field lines in this region.

In experiment 4, the current in coil 2 is reversed so that the direction of the magnetic field produced by coil 2 is also reversed. The magnitudes of the currents in coil 1 and coil 2 are still 225 mA.

Sketch a graph to show how B_H varies between x = 0 and x = r. The x-axis has been provided for you.

Your graph should include numerical values on your B_H axis that correspond to x = 0 and x = r.