Lessons · Teaching · circuits and magnets
A circuit has to be a complete loop
Current flows only around a complete loop from one terminal of a cell, through the components, and back to the other. A switch works by breaking the loop. Conductors let current pass and insulators do not. Magnets attract magnetic materials and have two poles that behave oppositely.
Hone is a place to practise a career, one idea a day. This is one of its lessons, written out in full and free to read without an account.
In beta. This lesson was written for Hone and has not yet been checked by a state certification officer. Practice material, not professional advice. What that means.
What it is for
'The battery sends electricity to the bulb' leaves out the return path, and a pupil who believes it will wire a circuit with one wire and be puzzled. The loop is the idea, and building one wrong is the fastest way to learn it.
How to think about it
Trace the loop with a finger from one terminal all the way back to the other. If the finger cannot get home, nothing lights. Then add components: in series the current has one path, so a break stops everything; in parallel there is more than one, so the others carry on.
Worked example
Current flows only if the loop is complete from one terminal back to the otherTrace it with a finger. A gap anywhere stops everything.
A switch is a deliberate gap you can open and closeWhich is all a switch has ever been.
In series one break stops all of it; in parallel the other branches keep workingWhich is why house lights are not wired in series.
Like poles repel and unlike poles attract; magnetism works through a gapNot every metal is magnetic: aluminium and copper are not.
Your turn
Name what a circuit must form for current to flow.
Current flows only around a complete
Solve one, graded on the server
The trap
Saying all metals are magnetic. Iron, nickel and cobalt are; aluminium, copper and gold are not, and a class testing coins will find that out within a minute.