STP Physical Sciences 4

Question 1

In computed tomography (CT), what does the Hounsfield unit (HU) scale measure?

Accepted Answer

The relative linear attenuation coefficient of tissue compared to water

Answer

Hounsfield units quantify X-ray attenuation relative to water (HU=0) and air (HU=−1000), enabling tissue differentiation in CT images.

Question 2

What property of a thermistor makes it useful as a temperature sensor?

Accepted Answer

Its resistance changes significantly and predictably with temperature

Answer

Thermistors exhibit a large, reproducible change in electrical resistance with temperature, making them sensitive and practical temperature sensors.

Question 3

What is the Larmor frequency in MRI physics?

Accepted Answer

The resonant precession frequency of nuclei in a magnetic field

Answer

The Larmor frequency ω₀ = γB₀ is the frequency at which nuclear spins precess around the applied magnetic field, and is used for RF excitation in MRI.

Question 4

Which radiation protection principle requires that doses be kept as low as reasonably practicable?

Accepted Answer

Optimisation (ALARP)

Answer

The ALARP (As Low As Reasonably Practicable) principle, also called optimisation, requires reducing radiation doses as far as reasonably achievable.

Question 5

A sinusoidal AC signal has a peak voltage of 340 V. What is its RMS voltage?

Accepted Answer

240 V

Answer

V_rms = V_peak / √2 = 340 / 1.414 ≈ 240 V, which is the standard UK mains supply RMS voltage.

(STP) Scientist Training Programme Practice Test

(STP) Scientist Training Programme Practice Test

STP Physical Sciences 4