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A cell gives a current of 0.15A through a resistance of 8...

A cell gives a current of 0.15A through a resistance of 8\(\Omega\) and 0.3A. When the resistance is changed to 3\(\Omega\) the internal resistance of the cell is

A.

0.05\(\Omega\)

B.

1.00\(\Omega\)

C.

1.50\(\Omega\)

D.

2.00\(\Omega\)

E.

2.50\(\Omega\)

Correct answer is D

The E.M.F of a circuit is given by 

\(E=I(R+r)\)

Hence, E = 0.15(8+r)  = 0.3(3+r)

1.2 + 0.15r = 0.9 + 0.3r

1.2 - 0.9 = 0.3r - 0.15r

0.3 = 0.15r

r = \(\frac{0.3}{0.15}\)

r = 2\(\Omega\)