Question

Internal resistance of primary cell is 8 Ohm. It generates a current of 0.4A in an external resistance of 21 ohm. The rate at which chemical energy id consumed in providing the current is -

A) 3.12 J/S

B) 4.64 J/S

C) 5.36 J/S

D) 1.32 J/S
​

Answer 1

The total resistance of a circuit connected to the given cell of emf 15 V is the sum of all the resistances from various sources like, resistors, ammeter, voltmeter, etc., connected in series along with the internal resistance of the cell.

In this case, the total resistance is given as 3Ω+3Ω+6Ω=12ohms.

From the ohm's law the total current can be calculated from the formula I=V/R.

That is, I=

R

V

=

12A

15V

=1.25A.

Hence, the current through the battery is 1.25 amperes.

The voltage output of a device is measured across its terminals and is called its terminal voltage V. Terminal voltage is given by the equation V=emf−Ir where, r is the internal resistance and I is the current flowing at the time of the measurement.

Therefore, V=15V−(1.25×3)=11.25V.

Hence, the potential difference across the terminals of the cell is 11.25V

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