A storage battery of emf 8.0 V and internal resistance 0.5`Omega` is being charged by a 120 V de supply using a series resistor of 15.5`Omega`. What is the terminal voltage of the battery during charging? What is the purpose of having a series resistor in the charging circuit?

Explanation

`E=V+1(R_r) `
`I=(E=V)/(R+V)=(120-8)/(15.5+0.5)=7A`
Terminal voltage =+ `(7xx0.5)=11.5V` The series resistor limits the current drawn from the external source. In its absence, the current will be dangerously high.