Question

A storage battery is of emf 8V and internal resistance 0.5 ohm is being charged by d.c supply
of 120 V using a resistor of 15.5 ohm
a) Draw the circuit diagram.
b) Calculate the potential difference across the battery.
c) What is the purpose of having series resistance in this circuit?

Answer 1

Explanation:

E=8V, internal resistance R  

1

​  

=0.5Ω

V=120V, resistance R  

2

​  

=15.5Ω

Effective voltage V  

′

 

=V−E=112 V

I=  

R  

1

​  

+R  

2

​  

 

V  

′

 

 

​  

=7 A

Voltage across R  

1

​  

=IR  

1

​  

=3.5 V

Terminal voltage =8+3.5=11.5 V

Series resistor in the charging circuit limits the current drawn from the external source.

Answer 2

Answer:

ANS AS FOLLOWS

Explanation:

current i =v1-E/R+r=120-8/15.5+0.5

             =7A

∴∴ Terminal voltage of battery during charging,

V = E + Ir = 8 + 7 x 0.5 = 11.5 V

(c) Series resistance controls the current drawn from external supply. In its absence, the current during the charging will be dangerously high.