Question

34. A storage battery of e.m.f. 12.0 V and internal
resistance 0.5 12 is to be charged by a 120V
d.c. supply of negligible internal resistance
What resistance is required in the circuit for
the charging current to be 3 A ? What is the
terminal voltage of the battery during
charging?​

Answer 1

Solution :-

As per the given data ,

• EMF(E) = 12 V
• Internal resistance (r) = 0.5 Ω
• Current flowing through the circuit (I) = 3 A
• Voltage of the DC supply(V) = 120 V

(1)

As per the formula ,

➜ I =  (V-E) ÷ (R +r)

Now let's substitute the given values in the above equation ,

➜ 3  = 120 - 12 / R + 0.5

➜ 3 R + 1.5 = 108

➜ 3R = 108 - 1.5

➜ 3R = 106.5

➜ R = 106.5 / 3

➜ R = 35.5 Ω

The resistor required to provide a charging current of 3 A is 35.5 Ω.

(2)

➜ Terminal voltage = E - I r

➜ Terminal voltage = 12 - 3 x 0.5

➜ Terminal voltage = 12 - 1.5

➜ Terminal voltage = 10.5 V

The terminal voltage of the battery during charging is 10.5 V