ScienceGrade 9ages 14–15
🔌 Resistance and current
Charge moving through a wire is constantly colliding with the atoms inside it, and every collision slows it down — which is exactly why a thin, long wire carries less current than a thick, short one, not more.
Try this lesson freeNo card needed. The first lesson is free.
Download on the App StoreWhat your child learns
- Charge moving in a wire keeps colliding with the atoms inside it, and every collision holds it back.
- A narrow wire squeezes the passage, so it brings more collisions for each charge that passes.
- A long wire adds more and more distance over which those collisions repeat.
- So thin and long together give the greatest resistance, and at the same voltage the smallest current.
The mistake most kids make here
The battery is the resistance, and a thin wire always carries more current.
Try one question
If voltage stays and resistance rises, current…
The current
- always rises
- falls
- turns into water
Answer
falls — Yes. The same push against more collisions moves less charge each second.
How Maya teaches it
Your child tells Maya what they did in class. She teaches this topic at her desk, asks questions with tappable answers, and when the answer is wrong she explains why that answer was tempting instead of saying “try again”. She remembers what did not land and comes back to it.
Your child has it when they can: Say what happens to current when resistance rises, and what is not resistance.
How to help at home
Resistance comes from the wire itself, not the battery — it's how much a wire's atoms get in the way of charge trying to move through it. A narrow wire squeezes the path, forcing more collisions for every bit of charge that passes.
Length matters too: a longer wire just adds more distance over which those collisions keep happening, so a thin, long wire has the highest resistance of all.
Ask your child: if the voltage pushing the charge stays the same but the resistance goes up, does more or less charge get through each second? Since the same push now faces more collisions, less charge moves — so current falls.
A good sign they've got it: they can say that resistance lives in the wire (not the battery), that thinner and longer both raise resistance, and that at a fixed voltage, higher resistance always means lower current.
Questions parents ask
- Why does a thin wire carry less current, not more?
- A thin wire squeezes the path charge has to move through, causing more collisions with the wire's atoms for every bit of charge. More collisions mean more resistance, and more resistance means less current at the same voltage.
- Is the battery the resistance in a circuit?
- No. Resistance comes from the wire (and any component in the circuit) getting in the way of moving charge. The battery provides the voltage that pushes the charge — it isn't the obstacle.
- What happens to current if resistance goes up but voltage stays the same?
- Current goes down. The same push (voltage) now has to move charge through more collisions, so less charge gets through each second.
- How does Maya teach this instead of just giving the formula?
- Maya asks what happens to current as resistance rises, with real options, so the child reasons through the collisions in the wire instead of only memorizing that 'V equals I times R.'
No card needed. The first lesson is free.
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Sources: Next Generation Science Standards