JAMB - Physics (1979 - No. 40)
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
0.5 ohm
0.62 ohm
1.0 ohm
2.0 ohm
3.0 ohm
Explanation
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 \(\Omega\)
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