A cell of e.m.f 1.5V, records a p.d of 1.3V, when connected to an external resistance R, such that current flowing through circuit is 0.25A. Calculate the value of R and internal resistance of cell
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A battery of e.m.f 15 V and internal resistance 3 ohm is connected to two resistors of resistances 3 ohm and 6 ohm in series. The p.d between the terminals of the battery is
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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