AQA A Level Physics Paper 3 Section B: Medical physics June 2024 question paper 7408/3BB

A human eye has a far point of 6.0 m.

State the name of this defect of vision.

Calculate the power of the correcting lens required for this eye.

An eye with astigmatism requires the following prescription:

−4.00 –0.75 ×30

Which row identifies the meaning of each number?

A stadium is full of spectators. The peak sound-intensity level at the centre of the stadium is 110 dB.

On another occasion the number of spectators in the stadium is reduced by 60%.

Estimate the peak sound-intensity level at the centre of the stadium.

You should assume that on both occasions:

• the sound intensity produced by each spectator is the same

• the spectators are distributed evenly around the stadium.

Describe the changes to a person’s hearing that may result from prolonged exposure to sound at 110 dB.

Name the two types of optical fibre bundle used in an endoscope. Go on to discuss whether the optical fibres in either of these bundles require cladding.

Modal and material dispersion can cause problems in fibre-optic communications.

Discuss why the methods used to reduce modal and material dispersion are not required in an endoscope.

In your answer you should:

• describe the methods used to reduce dispersion in an optical fibre used for communication

• explain why the methods are not required in an endoscope

• explain how using these methods in an endoscope would affect its function.

Fluorine-18 has a biological half-life of 6.0 hours.

Explain what is meant by this statement.

In a PET scan, fluorine-18 is used as a tracer and is injected into the person being scanned.

The physical half-life of fluorine-18 is 110 minutes.

Calculate the percentage of fluorine-18 that remains in the person 4.0 hours after it is injected.

Name the particles emitted when a fluorine-18 nucleus decays.

Figure 1 shows the cross-section of a body inside a ring of detectors during a PET scan. The side of each square represents 5 cm.

One of the products from the fluorine-18 decay goes on to produce two new particles. These particles travel in opposite directions in the plane shown in Figure 1. The particles are then detected by the detectors labelled A and B. Detector A detects a particle 0.79 ns before detector B.

Determine the square in Figure 1 in which the particles were produced. You should identify the square with a letter and a number, eg B 5.

Figure 2 shows a transducer used in a medical ultrasound scanner.

Explain why a backing material is used.

A beam of ultrasound is transmitted from muscle into bone.

Calculate the percentage of the incident intensity that is transmitted.

acoustic impedance of bone = 5.3 × 10⁶ kg m⁻² s⁻¹