Question

A portable x-ray unit has a step-up transformer. The 120 V input is transformed to the 100 kV output needed by the x-ray tube. The primary has 47 loops and draws a current of 16 A when in use. What is the current output of the secondary in milliAmpere

Answer 1

The number of loops in the primary winding of the transformer draws our attention to it like some kind of consciousness-magnet. But if and when we start to actually THINK about this question, we notice a subtle bad smell, and we realize that the number of loops in the transformer is a total red herring, and we don't need to worry about it at all.

-- The electrical power coming out of the transformer is equal to the electrical power going into it.

-- Electrical power = (voltage) x (current)

-- Power going in = (120 V) x (16 A) = 1,920 watts

-- Power coming out = (100,000 V) x (current)

100,000v x current = 1,920 W

Current = 1,920 W / 100,000 V

Current = 0.0192 A

Current = 19.2 milliAmperes

Leave the red herring where we found it and let it rot.