Question 30
Current ElectricityIn the circuit above, the ammeter reads a current of 5.0 A when R = 8 Ω and reads 7.0 A when R = 5 Ω. The value of the unknown resistance X is
- A.10.0 Ω
- B.7.5 Ω
- C.5.0 Ω
- D.2.5 Ω
Show the answer and explanation
Answer: D (2.5 Ω)
Explanation
E = I(R + X) in both cases: 5(8 + X) = 7(5 + X), so 40 + 5X = 35 + 7X and X = 2.5 Ω.