CIE iGCSE Co-Ordinated Science P2.2.2 Melting, boiling and evaporation Exam Style Questions Paper 3
Question
Another student wears a white T-shirt in the Sun and does not become as hot.
Explain why.
Most-appropriate topic codes (Cambridge IGCSE Coordinated Sciences 0654):
• Topic P1.2 — Motion (Part (a)(i))
• Topic P1.6.4 — Power (Part (a)(ii))
• Topic P2.2.2 — Melting, boiling and evaporation (Part (b)(i))
• Topic P2.3.3 — Radiation (Part (b)(ii))
• Topic P6.2.1 — The Sun as a star (Part (b)(iii), (b)(iv))
▶️ Answer/Explanation
(a)(i) evidence of total time = 15 (s); v = s/t (in any form) OR (average speed =) 100/15; 6.7 (m/s)
Total time = 3.7 + 3.1 + 2.6 + 2.6 + 3.0 = 15.0 s. Average speed = 100/15 = 6.7 m/s.
(a)(ii) P = W/t (in any form) OR (work done =) 600 × 3.0; 1800; J
Work done = power × time = 600 × 3.0 = 1800 J. The unit for work is the joule (J).
(b)(i) evaporation
Sweating cools the body because the most energetic water particles evaporate from the skin surface, taking thermal energy with them and lowering the skin temperature.
(b)(ii) white absorbs less (thermal) radiation / white reflects more (thermal) radiation
White surfaces reflect most incident radiation, so less thermal energy is absorbed. Black surfaces absorb more radiation, leading to greater heating.
(b)(iii) helium or hydrogen
The Sun is composed mainly of hydrogen (about 75%) and helium (about 25%), with small amounts of other elements.
(b)(iv) infrared; (visible) light; ultraviolet
The Sun emits energy across the electromagnetic spectrum, but most is in the infrared, visible, and ultraviolet regions.
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.