Question

find the value of emf e when Ammeter reads 3 A current flowing through it​

Answer 1

Answer ⇒ Option (c).

Explanation ⇒ Current through 3 ohm resistor is 3 A.

Hence, Potential difference across it = 9 V.

Now, in the closed loop,

12 - 9 - 6i = 0 [Kirchoff's second law.]

∴ 3 - 6i = 0

∴ i = 1/2 A.

This means, current through 3 ohm is 3 A and current in 6 Ohm is 1/2 A. Hence. Current going in an cell of emf e is  3 - 1/2 A

= 5/2 A.

Hence, current going in 6 ohm resistor is 5/2 A.

Now, in another loop,

-ε + 6 × 5/2 - 6 × 1/2 = 0

∴ ε = 15 - 3

∴ ε = 12 V.

Hence, Option (c). is correct.

Hope it helps.

Answer 2

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