A cell of e.m.f. 1.5v is connected in series with a resistor of 3\(\Omega\). A high resistance voltmeter connected across the cell registers only 0.9v. Calculate the internal resistance of the cell
A
5.0\(\Omega\)
B
4.5\(\Omega\)
C
2.4\(\Omega\)
D
2.0\(\Omega\)
E
1.8\(\Omega\)
Verified Correct Answer: D.
Physical Principles & Numerical Solution
E.M.F (E) = 1.5v, Internal Resistance (r) = ?, Potential Difference (V) = 0.9v, Load resistance (R) = 3\Omega,
Current (I) = V / R = 0.9 / 3 = 0.3A
USING : E = I ( R + r )
r = (E / I) - R = (1.5 / 0.3) - 3
r = 5 - 3
r = 2\Omega,
Source: Myschool Past Questions Archive (Record #33672)