Question 21
Current ElectricityA cell of internal resistance r supplies current to a 6.0 Ω resistor and its efficiency is 75%. Find the value of r.
- A.4.5 Ω
- B.1.0 Ω
- C.8.0 Ω
- D.2.0 Ω
Show the answer and explanation
Answer: D (2.0 Ω)
Explanation
Efficiency = R/(R + r): 0.75 = 6/(6 + r), so 6 + r = 8 and r = 2.0 Ω.