3 mistakes learners make with circuits, each one named and explained.
Current is not used up. It is the same all the way round a series circuit.
The current after a lamp is said to be smaller than the current before it.
The lamp clearly consumes something, and current is the thing that was flowing into it.
Question. Two lamps in series, points X before and Y after
A common answer. the current at X is larger
The answer. the current is the same at X and Y
Why. Charge cannot pile up or disappear inside the lamp; what the lamp uses is energy, not charge.
Current is how much charge passes each second. In a series loop it is the same everywhere.
Adding a resistor in parallel is said to leave the total resistance unchanged.
The original resistor is still exactly as it was, so it seems nothing has changed.
Question. A second identical resistor added in parallel
A common answer. the total resistance is unchanged
The answer. the total resistance halves
Why. The first resistor is unchanged, but there is now a second path alongside it.
Total resistance is about the whole circuit, not about any one component.
Two identical resistors in parallel are said to double the total resistance.
Adding components sounds like adding resistance, which is exactly what happens in series.
Question. Two identical resistors in parallel
A common answer. the resistance doubles
The answer. the resistance halves
Why. A second path is another route for the current, so more charge can flow, not less.
Think of doors out of a room. A second door never makes leaving harder.
WAJD spots these patterns in your child's answers and names the one behind their wrong answers, instead of just marking them wrong.