A cell can supply current of 0.8A and 0.4A through a 2\Omega and a 3\Omega resistors respectively. Calculate the internal resistance of the cell.
A
0.2Ω
B
0.4Ω
C
1.0Ω
D
3.0Ω
E
9.0Ω
Verified Correct Answer: C.
Physical Principles & Numerical Solution
Assume the internal resistor = R
Current with 2 Ohm Resistor = 0.80A
Voltage = (R + 2) x 0.80 = V ; That is 0.8R + 1.6 = V ———————[[1]
Current with 3 Ohm Resistor = 0.40 A
Voltage = (R+3) x 0.40 = V ; That is 0.4R + 1.2 = V ————————[[2]
Subtracting 1 from 2 gives
--> (0.8 - 0.4) R
( 1.6 - 1.2 )
( V - V )
Therefore
0.4R + 0.4 = 0
R = 0.4 /0.4 = 1 Ohms
Source: Myschool Past Questions Archive (Record #21254)