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Date	May 2021	Marks available	3	Reference code	21M.2.SL.TZ2.6
Level	Standard level	Paper	Paper 2	Time zone	2
Command term	Calculate	Question number	6	Adapted from	N/A

Question

A photovoltaic cell is supplying energy to an external circuit. The photovoltaic cell can be modelled as a practical electrical cell with internal resistance.

The intensity of solar radiation incident on the photovoltaic cell at a particular time is at a maximum for the place where the cell is positioned.

The following data are available for this particular time:

Operating current = 0.90 A
Output potential difference to external circuit = 14.5 V
Output emf of photovoltaic cell = 21.0 V
Area of panel = 350 mm × 450 mm

Explain why the output potential difference to the external circuit and the output emf of the photovoltaic cell are different.

[2]

Calculate the internal resistance of the photovoltaic cell for the maximum intensity condition using the model for the cell.

[3]

The maximum intensity of sunlight incident on the photovoltaic cell at the place on the Earth’s surface is 680 W m⁻².

A measure of the efficiency of a photovoltaic cell is the ratio

$\frac{energy available every second to the external circuit}{energy arriving every second at the photovoltaic cell surface} .$

Determine the efficiency of this photovoltaic cell when the intensity incident upon it is at a maximum.

[3]

State two reasons why future energy demands will be increasingly reliant on sources such as photovoltaic cells.

[2]

Markscheme

there is a potential difference across the internal resistance
OR
there is energy/power dissipated in the internal resistance ✓

when there is current «in the cell»/as charge flows «through the cell» ✓

Allow full credit for answer based on $V = ε - I r$

ALTERNATIVE 1
pd dropped across cell $= 6.5 « V »$ ✓

internal resistance $= \frac{6.5}{0.9}$ ✓

$7.2 « Ω »$ ✓

ALTERNATIVE 2

$ε = I (R + r)$ so $ε = V + I r$ ✓

$21.0 = 14.5 + 0.9 \times r$ ✓

$7.2 « Ω »$ ✓

Alternative solutions are possible

Award [3] marks for a bald correct answer

power arriving at cell = 680 x 0.35 x 0.45 = «107 W» ✓

power in external circuit = 14.5 x 0.9 = «13.1 W» ✓

efficiency = 0.12 OR 12 % ✓

Award [3] marks for a bald correct answer

Allow ECF for MP3

«energy from Sun/photovoltaic cells» is renewable
OR
non-renewable are running out ✓

non-polluting/clean ✓

no greenhouse gases
OR
does not contribute to global warming/climate change ✓

OWTTE

Do not allow economic aspects (e.g. free energy)

Examiners report

[N/A]

Syllabus sections

Core » Topic 5: Electricity and magnetism » 5.3 – Electric cells

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