iGCSE Physics (0625) 2.1.1 States of matter Paper 4 -Exam Style Questions- New Syllabus
Question
Fig. 3.1 shows a small block of ice floating in a beaker of warm water.
(i) State the name of the thermal process that transfers energy from the water to the ice.
(ii) Initially, there is 0.34kg of water in the beaker. The specific heat capacity of water is 4200J/(kg°C). Calculate the energy transferred from this water as its temperature decreases from 28°C to 10°C.
(iii) The temperature of the water near the ice decreases first. Explain how convection causes the temperature of all the water in the beaker to decrease.
(iv) State what happens to the internal energy of the water as the temperature of the water decreases. Describe the change in terms of the energy of the particles.
Most-appropriate topic codes (Cambridge IGCSE Physics 0625):
• Topic 2.1.1 — States of matter (Part (a))
• Topic 2.3.1 — Conduction (Part (b)(i))
• Topic 2.2.2 — Specific heat capacity (Part (b)(ii))
• Topic 2.3.2 — Convection (Part (b)(iii))
• Topic 2.2.2 — Specific heat capacity (Part (b)(iv))
▶️ Answer/Explanation
Correct Answer: (they / particles in ice) vibrate (about a fixed position) OR particles in water move throughout the liquid
Detailed solution: In a solid like ice, particles are held in a fixed lattice structure by strong intermolecular forces, so their motion is restricted to vibration about a fixed position. In a liquid like water, particles have more kinetic energy, allowing them to overcome some of these forces and move freely throughout the volume of the liquid.
Correct Answer: conduction
Detailed solution: Conduction is the transfer of thermal energy through a substance or between substances in direct contact via particle collisions. The ice and the warm water are in direct physical contact, so energy transfers from the higher-energy water particles to the lower-energy ice particles across the boundary.
Correct Answer: $2.6 \times 10^4\text{ J}$
Detailed solution: The energy transferred is calculated using $\Delta E = mc\Delta\theta$. The mass $m = 0.34\text{ kg}$, specific heat capacity $c = 4200\text{ J}/(\text{kg}^\circ\text{C})$, and temperature change $\Delta\theta = 28^\circ\text{C} – 10^\circ\text{C} = 18^\circ\text{C}$. The calculation is $0.34 \times 4200 \times 18 = 25704\text{ J}$, which is $2.6 \times 10^4\text{ J}$ to two significant figures.
Correct Answer: density (of water next to the ice) increases cold(er) water sinks warm(er) water replaces cold water OR warm(er) water rises OR making a convection current
Detailed solution: As water near the ice cools, its particles lose kinetic energy and move closer together, causing its density to increase. This denser, colder water sinks to the bottom of the beaker. Warmer, less dense water from below is displaced and rises to the top, creating a convection current that circulates and cools all the water.
Correct Answer: internal energy decreases AND (average) kinetic energy (of particles) decreases
Detailed solution: The internal energy of a substance is the sum of the kinetic and potential energies of its constituent particles. When the temperature of the water falls, it indicates that the average kinetic energy of the water particles has decreased, resulting in a net decrease in the total internal energy of the water.