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NCERT Class XII Chapter
Current Electricity
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Question : 11 of 24
Marks: +1, -0
A storage battery of emf 8.0 V and internal resistance 0.5 Ω is being charged by a 120 V dc supply using a series resistor of 15.5 Ω. What is the terminal voltage of the battery during charging? What is the purpose of having a series resistor in the charging circuit?
Solution:  
During charging, the electric current is sent into the 8.0 V battery.
The current in the circuit
I = E1−E2Rext+r\frac{E_1-E_2}{R_{ext}+r} = 120−815.5+0.5\frac{120-8}{15.5+0.5}
or I = 11216\frac{112}{16} = 7 A
Now, terminal voltage of the battery during charging
V = E + Ir = 8 + 7(0.5) = 11.5 V
A series resistance is joined in the charging circuit to limit the excessive current so that charging is slow and permanent.
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