In a given circuit, the cell P has an emf 1.5V and an unknown internal resistance while cell Q has an emf 2.0V and an internal resistance of 1 ohm if the ammeter reads 50m A, Then r is equal to
Attached Figure / Diagram
A
0.5 ohm
B
0.62 ohm
C
1.0 ohm
D
2.0 ohm
E
3.0 ohm
Verified Correct Answer: D.
Physical Principles & Numerical Solution
Total emf in the circuit (E) = 2.0 - 1.5 = 0.5V ( due to nature of the connection; +ve terminal to -ve terminal)
Total resistance in the circuit(both r & R) = 7 + 1 + x = 8 + x
Using, E = I(R + r)
E = I(R + r)
0.5 = 50 x 10\(^{-3}\)(8 + x)
8 + x = \(\frac{0.5}{50 \times 10^{-3}}\)
8 + x = 10
x = 10 - 8 = 2 \(\Omega\)
Source: Myschool Past Questions Archive (Record #41597)