The Basic lessons · Basic electronics and theory · B-005-011

Transformers, Magnetic Fields, and Energy Transfer

Learn how transformers change voltage and current while keeping power balanced, and understand how magnetic fields behave around wires. This lesson explains why wires get warm and how to maximize energy transfer between circuits.

This lesson is part of SignalPrep Pro. The subsection's 11 exam questions are free to practise: practise B-005-011.

What this subsection asks

• A transformer with a 120-volt primary voltage supplies 250 watts to a transmitter. Neglecting losses, what is the approximate primary current?
• How can a transformer with two windings change impedance?
• A transformer with a single 12-volt secondary draws 0.5 amperes through its 120-volt primary. Assuming no losses, what current is drawn from the secondary?
• The primary winding of a transformer has 250 turns, and the secondary has 500 turns. If the input voltage is 120 volts, what is the secondary voltage?
• The strength of the magnetic field around a conductor in air is:
• Maximum induced voltage in a coil occurs when:
• A transformer primary winding consumes 10 watts. Neglecting losses, if the secondary voltage is 5 volts, what is the secondary current?
• 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?
• When is coupling (induction) between two wires maximum?
• A permanent magnet would most likely be made from:
• What confirms the fact that the transfer of energy from the primary to the secondary of a transformer is not perfect?