Edexcel IGCSE Physics 5.11P Change-of-State Practical

Practise obtaining and interpreting temperature–time graphs with a constant-temperature plateau during a change of state.

[Maximum number: 4]

This question is about specific heat capacity.

After finishing the experiment, the student removes the aluminium block and places the container of water into a freezer.

The water loses energy at a constant rate and cools from $38^{\circ} \mathrm{C}$ to $-20^{\circ} \mathrm{C}$ .
The water freezes and turns into ice at $0^{\circ} \mathrm{C}$ .
Ice has a lower specific heat capacity than water.
Use the axes to sketch a temperature-time graph from when the water is placed in the freezer until it reaches its lowest temperature.

No calculations are required.

Figure for Question 5.11P Change of state practical question 1 — Edexcel IGCSE Physics

Marking points:
- line has two downward sloping sections of different gradient
- horizontal line at $0^\circ\mathrm{C}$ between the downward sloping sections
- line starts at $38^\circ\mathrm{C}$ and finishes at $-20^\circ\mathrm{C}$
- initial downward sloping line has smaller gradient than final downward sloping line

Ignore:
- where lines intersect the time axis
- start or finish time

Marking guidance:
- Sections do not need to be straight, but one must be clearly steeper than the other.
- Reject the horizontal-line marking point if there is more than one horizontal line lower than $38^\circ\mathrm{C}$ and higher than $-20^\circ\mathrm{C}$ .
- Judged by eye.
- Responses with initial and final downward sections parallel by eye can only score the horizontal-line and start/finish marking points.

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5.11P Change of state practical question 1