Physics
Physics
Problem
An ideal mains transformer, working with a supply voltage of 240 V, has 2000 turns on its primary coil and 100 turns on its secondary coil. The transformer is used to operate a laptop computer, through which a current of 4 A flows. The best estimate of the current flowing in the primary coil is a. 2 mA. b. 20 mA. c. 200 mA. d. 2 A.Intuitive explanation
The key to this problem is the transformer equation, which relates voltage and current changes to the ratio of coil turns. Since an ideal transformer conserves power, the voltage steps down by the same factor that the current steps up—so a smaller secondary voltage requires a larger secondary current to deliver the same energy. Use the turn ratio to find the secondary voltage, then apply power conservation () to find the primary current.
Intuitive explanation
The key to this problem is the transformer equation, which relates voltage and current changes to the ratio of coil turns. Since an ideal transformer conserves power, the voltage steps down by the same factor that the current steps up—so a smaller secondary voltage requires a larger secondary current to deliver the same energy. Use the turn ratio to find the secondary voltage, then apply power conservation () to find the primary current.