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Practical electricity experiment questions

Q2.

(a) An engineer wants to use solar cells to provide energy for a filament lamp in a road sign.

The engineer first investigates the emf and internal resistance of a solar cell under typical operating conditions. She determines how the potential difference across the solar cell varies with current.

The results are shown in the graph in below:

(i) The engineer used the graph to deduce that when operating in typical conditions a single solar cell produces an emf of 0.70 V and has an internal resistance of 8.0 Ω.

Explain how she used the graph to obtain the values for the emf and internal resistance of the solar cell.

[2 marks]

(ii) To operate effectively the lamp in the road sign needs a minimum current of 75 mA.

At this current the resistance of the filament lamp is 6.0 Ω.

The engineer proposes to try the two circuits shown below:

Deduce, using calculations, whether the circuits are suitable for this application.

[4 marks]

(b) Solar cells convert solar energy to useful electrical energy in the road sign with an efficiency of 4.0%. The solar-cell supply used by the engineer has a total surface area of 32 cm2 .

Calculate the minimum intensity, in W m–2 , of the sunlight needed to provide the minimum current of 75 mA to the road sign when it has a resistance of 6.0 Ω.

[3 marks]

(Total 9 marks)