# Question 8

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8.1 In the circuit below the battery has an emf (ε) of 12 V and an internal resistance of 0,2 Ω. The resistances of the connecting wires are negligible.

8.1.1 Define the term emf of a battery. (2)

8.1.2 Switch S is open. A high-resistance voltmeter is connected across points a and b.
What will the reading on the voltmeter be? (1)

8.1.3 Switch S is now closed. The same voltmeter is now connected across points c and d.
What will the reading on the voltmeter be? (1)

When switch S is closed, the potential difference across the terminals of the battery is 11,7 V.

Calculate the:
8.1.4 Current in the battery (3)
8.1.5 Effective resistance of the parallel branch (2)
8.1.6 Resistance of resistor R (4)

8.2 A battery with an emf of 12 V and an internal resistance of 0,2 Ω are connected in series to a very small electric motor and a resistor, T, of unknown resistance, as shown in the circuit below.

The motor is rated X watts, 3 volts, and operates at optimal conditions.

When switch S is closed, the motor lifts a 0,35 kg mass vertically upwards at a constant speed of 0,4 m∙s-1. Assume that there is no energy conversion into heat and sound.

Calculate the value of:
8.2.1 X (3)
8.2.2 The resistance of resistor T (5)

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