Question

A voltmeter is connected in parallel with a variable resistance, R which is in series with an ammeter and a cell. The cell is of e.m.f,E and internal resistance. For one value R¹,of the variable resistance, the ammeter 0.3A and the voltmeter reads 0.9V.For another value R² of the variable resistance, the ammeter reads 0.25A and the voltmeter reads 1.0V.Neglecting the resistance of the meters. Find the values of R¹,R²,E and r.

Answer 1

Answer:

The internal resistance of the cell is 2 ohms...

Explanation:

Let E be the emf of the cell and r be it's internal resistance

In the circuit the voltage equation can be written as,

E - Ir - IR = 0, where I = ammeter reading

but IR = V = voltmeter reading

=> E - Ir - V = 0

=> E = Ir + V

from case-I

E = 0.3r + 0.9

from case-II

E = 0.25r + 1

equating both the equation,

0.3r + 0.9 = 0.25 r + 1

=> 0.05r = 0.1

=> r = 0.1/0.05 = 2 ohms

Hence the internal resistance of the cell is 2 ohms.