DP Physics (last assessment 2024)

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Question 21M.2.SL.TZ2.6

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Date May 2021 Marks available [Maximum mark: 10] Reference code 21M.2.SL.TZ2.6
Level SL Paper 2 Time zone TZ2
Command term Calculate, Determine, Explain, State Question number 6 Adapted from N/A
6.
[Maximum mark: 10]
21M.2.SL.TZ2.6

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

(a)

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

 

[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-Ir

(b)

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

 

[3]

Markscheme

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

internal resistance =6.50.9 ✓

7.2 «Ω»✓


ALTERNATIVE 2

ε=I(R+r) so ε=V+Ir ✓

21.0=14.5+0.9×r ✓

7.2 «Ω» ✓


Alternative solutions are possible

Award [3] marks for a bald correct answer

(c)

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

energy available every second to the external circuitenergy 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]

Markscheme

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

(d)

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

[2]

Markscheme

«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)

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