9.1 Learners investigated the relationship between potential difference (V) and current (I) for the combination of two resistors, **R**_{1} and **R**_{2}. In one experiment, resistors **R**_{1} and **R**_{2} were connected in parallel. In a second experiment, resistors **R**_{1} and **R**_{2} were connected in series.

The learners then plotted graph **X**, the results of one of the experiments, and graph **Y**, the results of the other experiment, as shown below.

9.1.1 State Ohm’s law in words. (2)

9.1.2 What physical quantity does the gradient (slope) of the V-I graph represent? (1)

9.1.3 Calculate the gradient (slope) of graph **X**. (2)

9.1.4 Determine the resistance of resistor **R**_{1}. (4)

9.2 The circuit below consists of three resistors, **M**, **N** and **T**, a battery with emf Ɛ and an internal resistance of 0,9 Ω. The effective resistance between points **a** and **b** in the circuit is 6 Ω. The resistance of resistor **T** is 1,5 Ω.

When switch **S** is closed, a high-resistance voltmeter, V1, across **a** and **b** reads 5 V.

Calculate the:

9.2.1 Current delivered by the battery (3)

9.2.2 Emf (Ɛ) of the battery (4) Voltmeter V_{2} reads 2,5 V when the switch is closed.

9.2.3 Write down the resistance of **N**. (No calculations required.)

Give a reason for the answer. (2)

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