(a) The picture shows a person using a set of electronic ‘Body Fat Scales’. When the person stands on the scales, a small, harmless, electric current passes through the person’s body. The scales then calculate the resistance of the person’s body and convert the resistance into a prediction of body fat content.

(a) (i) The scales contain two 3 V cells joined in series.

Calculate the resistance of a person’s body, if when he stands on the scales, a current of 0.12mA passes through his body.

1000 mA = 1 A

Use the correct equation from the Physics Equations Sheet.

Show clearly how you work out your answer and give the unit.

Resistance = ...........................................

(3 marks)

 

(a) (ii) The scales can only produce a prediction of body fat content and not an accurate measurement.

Suggest why.

(1 mark)

(a) (iii) It is recommended that the scales are not used immediately after a person has drunk a large amount of water.

Suggest why.

(2 marks)

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(b) The diagram shows how someone could get an electric shock from accidentally cutting into an electric cable. If this happens, and a Residual Current Circuit Breaker (RCCB) is being used, the circuit will switch off automatically.

(b) (i) A faulty appliance or circuit can be switched off by a RCCB or a fuse.

Compare the action of a RCCB with the action of a fuse.

(2 marks)

(b) (ii) The graph shows how the severity of an electric shock depends on the size of the current and the time that the current flows through the body.

Using the RCCB helps prevent an electric shock seriously injuring the person using the hedge trimmers.

Using information from both the diagram and the graph explain how.

(2 marks)

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From Q6 P2 AQA June 2012 (Higher)