CIE iGCSE Co-Ordinated Science P4.2.4 Resistance Exam Style Questions Paper 3
Question
, for the doorbell.Most-appropriate topic codes (Cambridge IGCSE Coordinated Sciences 0654):
• Topic P4.3.1 — Circuit diagrams and circuit components (Part (a)(i))
• Topic P4.2.4 — Resistance (Part (a)(ii))
• Topic P5.2.2 — The three types of nuclear emission (Part (b)(i))
• Topic P5.2.4 — Half-life (Part (b)(ii))
• Topic P5.1 — The nucleus (Part (b)(iii))
▶️ Answer/Explanation
(a)(i) Correct symbol for battery and switch; series connections
The circuit diagram should show a battery, a switch, and the doorbell symbol connected in series with wires forming a complete loop.
(a)(ii) V = 4 × 1.5 OR 6.0 (seen); R = V/I (in any form) OR 6(.0)/3(.0); 2.0 (Ω)
Total voltage = 4 × 1.5 = 6.0 V. Using Ohm’s law, R = V/I = 6.0/3.0 = 2.0 Ω.
(b)(i) helium nucleus / 2 protons and 2 neutrons
An α-particle consists of 2 protons and 2 neutrons, which is identical to a helium-4 nucleus. It has a charge of +2e.
(b)(ii) decay rate needs to remain constant
A long half-life means the activity remains reasonably constant over the detector’s lifetime, so it does not need frequent replacement and remains reliable.
(b)(iii) 146
Number of neutrons = mass number – proton number = 241 – 95 = 146.
Question
Topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P4.3.1 — Circuit diagrams and circuit components
• Topic P1.6.3 — Energy resources
• Topic P4.2.4 — Resistance
• Topic P4.2.5 — Electrical energy and electrical power
• Topic P2.2.2 — Melting, boiling and evaporation
▶️ Answer/Explanation
(a) Motor: circle with ‘M’ inside. Variable resistor: rectangle (or zigzag) with a diagonal arrow across it.
The motor symbol indicates conversion of electrical energy to kinetic energy.
The arrow on the variable resistor symbol shows that its resistance can be adjusted, making it useful for controlling current in circuits such as dimmer switches or volume controls.
(b) Advantage: renewable / produces no greenhouse gases. Disadvantage: does not work at night / only works in sufficient sunlight.
Solar cells convert light energy directly into electricity with no fuel costs and zero emissions during operation.
However, their output depends entirely on sunlight availability, making them unreliable without battery storage, and initial installation costs can be high.
(c)(i) Current in the washing machine:
\(I = \dfrac{P}{V} = \dfrac{2500}{230} \approx \textbf{11\,A}\)
Using \(P = IV\) and rearranging for current, dividing the power (2500 W) by the supply voltage (230 V) gives approximately 10.87 A, which rounds to 11 A to 2 significant figures.
(c)(ii) Resistance of the heating element:
\(R = \dfrac{V}{I} = \dfrac{230}{3.0} \approx 77\,\Omega\)
Applying Ohm’s law \(V = IR\) and rearranging gives resistance as voltage divided by current.
The high resistance of the element is what causes electrical energy to be converted efficiently into heat.
(c)(iii) The most energetic particles near the liquid surface have enough kinetic energy to overcome intermolecular attractions and escape into the gas phase.
Because it is the fastest-moving particles that escape, the average kinetic energy of the remaining liquid falls, causing the liquid to cool.
Evaporation can occur at any temperature, unlike boiling which requires the entire liquid to reach a fixed boiling point.