A-level Physics (Advancing Physics)/Internal Resistance/Worked Solutions

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1. A 9V battery is short-circuited. The potential difference across the battery is found to be 8V, and the current is 5A. What is the internal resistance of the battery?

8 = 9 - 5Rinternal

5Rinternal = 1

Rinternal = 0.2Ω

Internal resistance q2.svg

2. What is the EMF of the battery in the following circuit?

Vexternal = 5 x 3 = 15 V

15 = E - (5 x 10)

E = 50 + 15 = 65 V

Internal resistance q3.svg

3. What is the internal resistance of the battery in the following circuit?

Vexternal = 7.5 x 3.75 = 28.125

Which actually makes this question impossible because the current is too high for the resistance supplied to the circuit.