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In a circuit (as shown in a figure), ideal ammeter and ideal voltmeter are used. Given EMF E = 4 V, external resistance R = 9 ohm, and internal resistance r = 1 ohm. Find the readings of the ammeter and voltmeter.

1. 1A, 3V
2. 2A, 3V
3. 1A, 4V
4. 2A, 4V

Correct answer: 1A, 3V

Solution

For the answer 1A, 3V: total resistance = E/I = 4/1 = 4 ohm. With r=1 ohm, external = 3 ohm. This implies the figure shows an arrangement where the effective external resistance is 3 ohm (e.g., R=9 ohm in parallel with 4.5 ohm, or another topology not visible in text). Terminal voltage = 4 - 1*1 = 3 V. Ammeter: 1A; Voltmeter: 3V.

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