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JAMB Physics 1993 Question 42

Question 42

Electrical Energy and Power

A 40-W instrument has a resistance of 90Ω. On what voltage should it be operated normally?

  1. A.60 V
  2. B.150 V
  3. C.225 V
  4. D.3600 V
Show the answer and explanation

Answer: A (60 V)

Explanation

P = V2/R, so V = √(PR) = √(40 × 90) = √3600 = 60 V.