CIE iGCSE Co-Ordinated Science P5.2.1 Detection of radioactivity Exam Style Questions Paper 3
Question
(a) A technician is checking for sources of radioactive emissions around a building.
(i) A radiation detector is placed in front of a source of ionising radiation. A piece of paper is placed in front of the source, and the radiation is no longer detected from the source. Identify the type of radiation being emitted by the source.
▶️Answer/Explanation
Alpha radiation (α). Alpha particles are stopped by a piece of paper, which is why the radiation is no longer detected when the paper is placed in front of the source.
(ii) The radioactive source is removed. State why the radiation detector continues to detect a small amount of radiation.
▶️Answer/Explanation
Background radiation. Even when the radioactive source is removed, the detector will still pick up background radiation from natural sources such as cosmic rays, rocks, and building materials.
(b) The graph in Fig. 9.1 shows the decay curve for a radioactive source.
Determine the half-life of the source. Show on the graph how you determined your answer.
▶️Answer/Explanation
The half-life is the time taken for the activity of the radioactive source to decrease to half of its initial value. To determine the half-life from the graph, identify the point where the activity is half of its initial value and read the corresponding time from the x-axis. For example, if the initial activity is 80 counts per second, the half-life is the time it takes for the activity to drop to 40 counts per second. This can be shown by drawing a horizontal line from 40 counts per second to the curve and then dropping a vertical line to the time axis.
(c) The radiation detector is powered by a battery. Fig. 9.2 shows the part of the electrical circuit which lights a lamp when the detector is switched on.
(i) The technician checks the potential difference across the lamp. On Fig. 9.2, add the circuit symbol for a meter to measure the potential difference across the lamp.
▶️Answer/Explanation
To measure the potential difference across the lamp, a voltmeter should be connected in parallel with the lamp. The circuit symbol for a voltmeter is a circle with a “V” inside it. Draw this symbol across the lamp in the circuit diagram.
(ii) The current supplied by the battery is 0.1A. The technician adds another cell to the battery. Describe how the current changes.
▶️Answer/Explanation
Adding another cell to the battery increases the voltage (potential difference) of the battery. According to Ohm’s Law (V = IR), if the resistance of the circuit remains constant, an increase in voltage will result in an increase in current. Therefore, the current in the circuit will increase.
(iii) Complete the sentence to describe current in metals.
Current in metals is due to the flow of ……
▶️Answer/Explanation
electrons. In metals, electric current is due to the flow of free electrons, which are negatively charged particles.