AQA A Level Physics Paper 3 Section A: Practical skills and data analysis June 2019 question paper 7408/3A

Figure 1 shows a sealed radioactive source used in schools and colleges.

State two safety procedures to reduce risk when using this type of source.

Safety procedure 1

Safety procedure 2

226²²⁶Ra A sealed source contains radium- (₈₈).

²²⁶₈₈Ra decays by emitting and ^– particles to produce²⁰⁶₈₂Pb which is stable.

Figure 2 is a graph of neutron number N against proton number Z, showing the different ways that²²⁶₈₈Ra can decay into²⁰⁶₈₂Pb.

Points A to M represent all the unstable nuclei that may be formed as²²⁶₈₈Ra decays into²⁰⁶₈₂Pb.

Determine the number of routes by which B can change into K.

Identify which of the nuclei A to M are common to all the possible ways that²²⁶₈₈Ra

The sealed source emits γ radiation in addition to and ^– particles. A student uses the sealed source to investigate the inverse-square law for γ radiation. The student begins by making measurements to find the count rate A_b for the background radiation.

State and explain procedures

to eliminate systematic error in the measurements used to find A_b

to reduce the percentage uncertainty in A_b.

Figure 3 shows an aluminium absorber placed between the sealed source and a radiation detector. This is to make sure that only γ radiation from the source reaches the detector.

The sealed source emits:

• particles with energy E_k between 3.8 MeV and 7.8 MeV

• ^– particles with energy E_k between zero and 5.5 MeV.

Figure 4 shows how the range of ^– particles in aluminium depends on E_k.

Deduce the minimum thickness of the aluminium absorber that should be used in the experiment.

Ionisation takes place inside the detector. The effective distance travelled by radiation from the source is (d + e). The distance e, shown in Figure 5, cannot be measured directly.

From the inverse-square law for radiation, it can be shown that

where A is the count rate, corrected for background radiation k is a constant. The student plots the graph of d against shown in Figure 6.

Deduce k using Figure 6. Explain your reasoning. Give a suitable unit for your result.

Determine e using Figure 6.

Figure 7 shows apparatus used to investigate the rate at which water flows through a horizontal cylindrical tube T of internal diameter d and length L.

The apparatus ensures that the water level in the can is at a constant height h above the centre of T.

Water flows out of T at a steady rate.

The volume flow rate through T is Q, where Q is in m³ s^–1. A student wants to measure Q as water flows through T.

Outline a procedure the student should follow to measure Q. Include in your answer

the measuring instruments used

how uncertainty in the measurements can be reduced.

It can be shown that

During the experiment the temperature is kept constant. Q is found for different values of h and a graph of these data is plotted, with Q on the vertical axis. The percentage uncertainty in the gradient of the graph is 6.4%.

The dimensions of tube T are measured and the uncertainties in these data are calculated.

The percentage uncertainty

In a different experiment, the horizontal tube T is connected to a vertical glass tube. Marks have been made at regular intervals on the glass tube. The student measures and records the vertical distance y between each of the marks and the centre of T.

She seals the open end of T and fills the glass tube with water, as shown in Figure 9

T is opened and water flows into a beaker. When the water level falls to the highest mark on the tube, she starts a stopwatch. She records the time t for the water to reach each of the other marks.

Explain how the student could check that the glass tube was vertical. You may wish to add detail to Figure 9 to illustrate your answer.

Figure 10 shows part of the graph drawn from the student’s data.

It can be shown that y decreases exponentially with t.

T₁₂ is the time for y to decrease by 50%, as shown in Figure 11.

The apparatus is adjusted so that the glass tube is inclined at 30 to the horizontal tube T, as shown in Figure 12.

The student measures and records the new values of y, the mean vertical distance between each of the marks and the centre of T. She then carries out the experiment as before, recording new values of t corresponding to each new value of y.

Draw a line on Figure 13 to show the graph produced using the modified apparatus. The dashed line is the original graph when the glass tube was vertical as shown in Figure 9.

A stationary wave is formed on a stretched wire.

Figure 14 shows the wire, fixed at one end, supported by two bridges and passing over a pulley.

A 0.500 kg mass is attached to the free end of the wire. A uniform horizontal magnetic field is applied perpendicular to the wire between the bridges. A signal generator is connected to each end of the wire.

The oscilloscope shown is used to determine the frequency of the output of the signal generator. The wire oscillates because the alternating current in the wire interacts with the magnetic field.

Figure 15 shows the first harmonic stationary wave produced when the distance x between the bridges is adjusted.

The output potential difference (pd) of the signal generator is displayed on the oscilloscope, as shown in Figure 16.

The time-base setting of the oscilloscope is 10 ms cm¹.

Determine f, the frequency of the alternating pd.

A metre ruler is placed next to the bridges supporting the wire, as shown in Figure 17

Determine c.

Determine, in kg m¹, the mass per unit length of the wire.

A student uses digital vernier callipers to measure the diameter of a cylindrical metal rod. The student places the rod between the jaws of the callipers and records the reading indicated. Without pressing the zero button, the student removes the rod and closes the jaws.

Figure 18 shows the calliper readings in millimetres, before and after the jaws are closed.

Calculate the diameter d of the rod.

Describe relevant procedures to limit the effect of random error in the result for d.

Determine the density of the rod. The mass per unit length of the rod is 3.54 10³ kg m¹.