Basic Qualification · B-005 Basic electronics and theory · B-005-011-008
A step-up transformer with a primary to secondary turns ratio of 1:5 delivers 50 milliamperes to a load. Assuming 100% efficiency, what is the primary current?
- A 2500 mA
- B 10 mA
- C 0.25 mA
- D 250 mA
Correct answer: D — 250 mA. From the official ISED question bank, verified word for word.
Why
With a 1:5 step-up transformer, the voltage increases five times, but to keep power constant at 100% efficiency, the current must drop by that same factor. The full explanation — and one for every question — is in Pro.
Practise this section
The theory: Ohm's law, power, series and parallel circuits, AC and DC, frequency and wavelength, decibels, and the metric prefixes the exam leans on.