Suppose a step-down transformer has a turns ration of 5:1. If the secondary current is 1A rms, what is the primary-current? A. 0.3 A B. 0.2 A C. 0.4 A D. 0.6 A E. None of the above

The answer is $\boxed{\text{B) 0.2 A}}$.

The turns ratio of a transformer is the ratio of the number of turns in the primary winding to

the number of turns in the secondary winding. In a step-down transformer, the turns ratio is greater than 1. This means that the voltage in the secondary winding is less than the voltage in the primary winding. The current in the secondary winding is greater than the current in the primary winding.

The current in the primary winding is equal to the current in the secondary winding times the turns ratio. In this case, the turns ratio is 5:1, so the current in the primary winding is 1A / 5 = 0.2A.

Option A is incorrect because the current in the primary winding cannot be

less than the current in the secondary winding. Option C is incorrect because the current in the primary winding cannot be twice the current in the secondary winding. Option D is incorrect because the current in the primary winding cannot be three times the current in the secondary winding. Option E is incorrect because the current in the primary winding must be greater than 0.