Name the unit for each electrical quantity, tell conductors from insulators, and explain what makes AC different from DC.
Syllabus: Current and voltage: terminology and units, conductors and insulators, alternating and direct current
Compendium articles on the ideas in this lesson, beyond what the exam asks.
Practise the 11 pool questions for this group. Answers are shuffled, and every one comes with a one-line "why".
A difference in voltage pushes electrons along. Their flow is current. Power is how fast electrical energy is used.
RememberVolts push. Amperes flow. Watts measure how fast energy is used.
In metals, outer electrons are loose and drift when voltage pushes them. In an insulator, every electron stays bound to its atom.
RememberMetals have many free electrons. Glass, plastic and air do not.
DC flows one way. AC alternates between positive and negative directions. Complete cycles per second is frequency, in hertz (Hz).
RememberAC swings both ways, not just to zero. Hertz = cycles per second.
Resistance opposes current of every kind: DC, AC and RF.