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Date	May 2017	Marks available	2	Reference code	17M.2.HL.TZ2.3
Level	Higher level	Paper	Paper 2	Time zone	2
Command term	Estimate	Question number	3	Adapted from	N/A

Question

The electrical circuit shown is used to investigate the temperature change in a wire that is wrapped around a mercury-in-glass thermometer.

A power supply of emf (electromotive force) 24 V and of negligible internal resistance is connected to a capacitor and to a coil of resistance wire using an arrangement of two switches. Switch S₁ is closed and, a few seconds later, opened. Then switch S₂ is closed.

The capacitance of the capacitor is 22 mF. Calculate the energy stored in the capacitor when it is fully charged.

[1]

The resistance of the wire is 8.0 Ω. Determine the time taken for the capacitor to discharge through the resistance wire. Assume that the capacitor is completely discharged when the potential difference across it has fallen to 0.24 V.

[3]

The mass of the resistance wire is 0.61 g and its observed temperature rise is 28 K. Estimate the specific heat capacity of the wire. Include an appropriate unit for your answer.

[2]

c.i.

Suggest one other energy loss in the experiment and the effect it will have on the value for the specific heat capacity of the wire.

[2]

c.ii.

Markscheme

« $\frac{1}{2}C{V^2} = \frac{1}{2} \times 0.22 \times {24^2}$ » = «J»

$\frac{1}{{100}} = {e^{ - \frac{t}{{8.0 \times 0.022}}}}$

$\ln 0.01 = - \frac{t}{{8.0 \times 0.022}}$

0.81 «s»

c = $\frac{Q}{{m \times \Delta T}}$

$\frac{{6.3}}{{0.00061 \times 28}}$

370 J kg^–1 K^–1

Allow ECF from 3(a) for energy transferred.

Correct answer only to include correct unit that matches answer power of ten.

Allow use of g and kJ in unit but must match numerical answer, eg: 0.37 J kg^–1 K^–1 receives [1]

c.i.

ALTERNATIVE 1

some thermal energy will be transferred to surroundings/along connecting wires/to
thermometer

estimate «of specific heat capacity by student» will be larger «than accepted value»

ALTERNATIVE 2

not all energy transferred as capacitor did not fully discharge

so estimate «of specific heat capacity by student» will be larger «than accepted value»

c.ii.

Examiners report

[N/A]

c.i.

[N/A]

c.ii.

Syllabus sections

Core » Topic 3: Thermal physics » 3.1 – Thermal concepts

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