A detector registers 96 counts per minute of background radiation. With a source present it registers 896 counts per minute initially and 496 counts per minute after 12 minutes.
.1
Calculate the initial corrected detected count rate in min−1 (counts per minute).
[2 marks]
.2
Determine the half-life in minutes.
[2 marks]
.3
Explain why the background must be subtracted before comparing the rates.
[2 marks]
6 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A 15 Ω resistor carries a current of 0.40 A for 200 s. Its resistance remains constant.
.1
Calculate the resistor's power.
[2 marks]
.2
Calculate the energy transferred in 200 s.
[2 marks]
.3
Predict and explain the effect on power of doubling current at the same resistance.
[2 marks]
5 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
A pure liquid cools at a steady rate of energy loss. Its temperature falls from 60 °C to 40 °C in 4 minutes, stays at 40 °C for 6 minutes, then falls below 40 °C.
024681012203040506070Time (min)Temperature (°C)
.1
Calculate the average rate of temperature decrease during the first 4 minutes, in °C per minute.
[2 marks]
.2
Explain the horizontal section and the fall afterwards on the temperature-time graph.
[3 marks]
5 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
Identical detectors at equal distances from two heated plates record infrared signal after the background reading has been subtracted. Both plates have the same area and temperature. Matt black gives 8.4 units and shiny silver gives 2.1 units.
.1
Calculate how many times larger the black-plate signal is.
[2 marks]
.2
Evaluate whether the measurements support using a shiny surface to reduce thermal radiation losses.
[3 marks]
4 marksFoundation and Higher
Spec and skills
Original practice question
Answer and supported method checks
An atom absorbs electromagnetic radiation and one electron moves to a higher energy level. Later the electron returns to its original level.
Explain the energy transfers and why the element does not change.
