CIE iGCSE Co-Ordinated Science P2.3.4 Consequences of thermal energy transfer Exam Style Questions Paper 3
Question
the water ……………………………..
the saucepan. …………………………
Complete Table 9.1 by placing ticks (✓) in the correct boxes to show which description describes a solid, a liquid and a gas.
Describe one difference between the magnetic properties of steel and the magnetic properties of soft iron.
Calculate the mass of the saucepan in grams.
The gravitational force on unit mass, \(g = 10 \, \text{N/kg}\).
to represent the hotplates.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P2.3.4 — Consequences of thermal energy transfer (Parts (a)(i)–(a)(ii))
• Topic P2.2.2 — Melting, boiling and evaporation (Part (a)(iii))
• Topic P2.1.1 — States of matter (Part (a)(iv))
• Topic P4.1 — Simple phenomena of magnetism (Part (b))
• Topic P1.3 — Mass and weight (Part (c))
• Topic P4.3.2 — Series and parallel circuits (Part (d))
▶️ Answer/Explanation
(a)(i) through the water: convection; through the saucepan: conduction.
In liquids, thermal energy is transferred mainly by convection — heated water near the bottom becomes less dense, rises, and cooler water sinks to replace it.
In solids such as the steel saucepan, thermal energy is transferred by conduction — vibrating particles pass energy to neighbouring particles without bulk movement of material.
Radiation can also occur from the outer surface of the pan, but convection and conduction are the main methods here.
(a)(ii) The temperature remains constant / stays at 100 °C while the water is boiling.
During boiling, all the energy supplied is used to overcome the intermolecular forces and convert liquid water to steam.
No energy goes into increasing the kinetic energy of the particles, so the temperature does not rise.
This energy used during a change of state is called latent heat of vaporisation.
(a)(iii) 100 °C
The boiling point of pure water at standard atmospheric pressure (101 325 Pa) is exactly 100 °C.
At higher pressures, the boiling point is higher; at lower pressures (e.g. at altitude), the boiling point is lower.
This fixed boiling point is used as one of the calibration points on the Celsius temperature scale.
(a)(iv) 
A gas expands to fill any container completely, so “takes up all the space available” describes a gas.
A liquid takes the shape of its container but has a definite volume, so the second description applies to a liquid.
A solid has a fixed shape and volume because its particles are held in fixed positions by strong intermolecular forces.
(b) Steel retains its magnetism better (is a permanent magnet); soft iron loses its magnetism more readily (is a temporary magnet).
Steel is a hard magnetic material — once magnetised it remains magnetised, making it suitable for permanent magnets.
Soft iron is an easy magnetic material — it is easily magnetised but loses its magnetism quickly when the external field is removed.
This makes soft iron suitable for electromagnet cores (e.g. in transformers and electric bells) where magnetism must be switched on and off.
(c) 1500 g
Using \(W = mg\), rearranged to \(m = \frac{W}{g} = \frac{15}{10} = 1.5 \, \text{kg}\).
Converting to grams: \(1.5 \, \text{kg} \times 1000 = 1500 \, \text{g}\).
The question specifically asks for the mass in grams, so the conversion from kg to g is essential for full marks.
(d) The completed circuit has: the 240 V supply connected to two branches in parallel, each branch containing a switch in series with a heater symbol. Correct symbol for switch; second heater connected in parallel; each heater controlled by a separate switch.
In a parallel circuit, each branch operates independently so each hotplate can be switched on or off without affecting the other.
A switch must be placed in series with each heater so that it can control that heater individually.
The circuit symbol for a heater is a rectangle with slanted lines inside (resembling a heating element).
Question
Only the water molecules with the greatest …………………………………………….. escape.
State the boiling point of water.
State what happens to the temperature of the water when it is boiling.
Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):
• Topic P4.3.2 — Series and parallel circuits (Part (a))
• Topic P2.3.4 — Consequences of thermal energy transfer (Part (b)(i)–(ii))
• Topic P2.2.2 — Melting, boiling and evaporation (Part (b)(iii)–(v))
▶️ Answer/Explanation
(a)(i) 6 A
Current is calculated using \( I = \dfrac{V}{R} \).
\( I = \dfrac{240}{40} = 6 \, \text{A} \).
(a)(ii) parallel
Fig. 6.2 shows both hotplates connected across the same two points of the supply.
This is the arrangement known as a parallel circuit.
(a)(iii) 20 Ω
For resistors in parallel, the combined resistance is always less than the smallest individual resistance.
Since both hotplates have equal resistance of \(40 \, \Omega\), the combined resistance is \(20 \, \Omega\).
(b)(i) conduction
Thermal energy passes through the solid metal base of the saucepan by conduction.
This occurs as vibrating particles pass on energy to neighbouring particles.
(b)(ii) arrows circulating upward then outward and down
Water heated at the bottom becomes less dense and rises.
Cooler, denser water then sinks to take its place, creating a circulating convection current.
(b)(iii) surface; energy
Evaporation occurs only at the surface of the liquid.
Only the water molecules with the greatest energy have enough energy to escape into the air.
(b)(iv) 100 °C
Water boils at \(100\,^\circ\text{C}\) at standard atmospheric pressure.
(b)(v) no change in temperature
While boiling, the extra thermal energy supplied is used to change state rather than raise temperature.
So the temperature of the water remains constant at \(100\,^\circ\text{C}\) throughout boiling.