Question

a cell of emf E volts and internal resistance r ohm when connected to an
external resistance of 1 ohm gives a current of 1 A and when it is connected to a resistance of 4 ohm gives current of 0.4 A. Find E and r.

Answer 1

I = E/(R+r)

I = current E = Emf R = external resistance

r = internal resistance

1 = E/(1+r)

E = 1+r

0.4 = E/(4+r)

E = 1.6 + 0.4r

1+r = 1.6 + 0.4r

0.6r = 0.6

r = 1 ohm

E = 1+r = 2 V

E =2V & r = 1 Ohm

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