Question

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

Answer 1

Given :

EMF of the cell = 1.5V

p.d. across terminals = 1.3V

Current flow in the circuit = 0.25A

To Find :

Value of E and internal resistance of the cell$.$

Solution :

■ For a cell of internal resistance r, the emf is

• e = V + Ir

✵ e denotes emf of battery

✵ V denotes terminal voltage

✵ r denotes internal resistance

By substituting the given values;

➠ e = V + Ir

➠ 1.5 = 1.3 + 0.25r

➠ 0.25r = 1.5 - 1.3

➠ 0.25r = 0.2

➠ r = 0.2/0.25

➠ r = 0.8 Ω

■ As per ohm's law current flow in circuit is directly proportional to the applied potential difference.

Therefore, V = IR

⭆ 1.3 = 0.25R

⭆ R = 1.3/0.25

⭆ R = 5.2 Ω