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JAMB Physics 2006 Question 27

Question 27

Alternating Current Circuits

When a certain a.c. supply is connected to a lamp, it lights with the same brightness as it does with a 12 V d.c. battery. The r.m.s. value of the a.c. supply is

  1. A.8.5 V.
  2. B.17.0 V.
  3. C.3.5 V.
  4. D.12.0 V.
Show the answer and explanation

Answer: D (12.0 V.)

Explanation

The r.m.s. value of an a.c. is the d.c. value that gives the same heating effect. Same brightness as 12 V d.c. means the r.m.s. voltage is 12 V.