A cell of emf 'E' and internal resistance 'r' is connected across a variable load resistor R. Draw the plots of the terminal voltage V versus (i) R and (ii) the current I. It is found that When R=4Ω, the current is 1 A and when R is increased to 9Ω, the current reduces to 0.5 A. Find the values of the emf E and internal resistance r.
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Solution
current in the circuit is given by
I=εR+r
Terminal voltage V=IR=VA−VBV=εIR+r=ε−IrI=ε4+r⟹r+4=ε⟶(1)0.5=ε9+r0.5r+4.5=ε⟶(2)