internal resistance of the D Cell Battery Measure potential

Measure potential difference across its terminals close switch rightarrow measure potential difference also assume the internal resistance of the battery is in series with resistor, Calculate internal resistance of the Battery. If oen: V_B - V_A = epsilon If Clsoe: TPD = epsilon - I_r r = epsilon - TPD/I

Solution

In OPEN circuit case :

--- > no current is flowing, so potential difference across terminal = emf of battery

Vb - Va = EMF = E = 1.518 V

In CLOSED case :

current flows in the circuit.

Applying KVL :

Vb - Va = E - I*r = 1.455

where I = current in the circuit

r = internal resistance of the battery

Now, I = E/(R+r) = 0.122 A

So, 1.518 - 0.122*r = 1.455

So, r = 0.516 ohm <------------answer