JAMB Physics 2007 Objective — Question 18
Question 18 of 50 from the Joint Admissions and Matriculation Board (JAMB) Physics 2007 Objective paper, with the correct answer and a full explanation.
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A 120V, 60W lamp is to be operated on a 220V a.c. supply mains. Calculate the value of non-inductive resistance that would be required to ensure that the lamp is run on correct voltage.
- A. 500 ohm
- B. 300 ohm
- C. 200 ohmCorrect
- D. 100 ohm
Explanation
I = P/V = 60/120 = 0.5A. Rin = 120/0.5 = 240 ohm. Rout = 220/0.5 = 440 ohm. Extra non-inductive resistance needed = 440-240 = 200 ohm.
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