What Actually Flows in a Wire
- Physics
- Ages 14–18 · Grades 9–12
- Hands-on experiment
What you’ll find out
- Current is a flow of charge and needs a complete loop.
- Voltage is the push that drives the current, not the thing that flows.
- Resistance opposes current, and the three quantities are linked by Ohm’s law.
No sign-up and no real names. In the lesson you check your understanding as you read, run the experiment yourself, and practise until it sticks.
It has to be a loop
A lamp does not use electricity up. Charge travels round a loop and returns to where it started. That loop is what a circuit is: charge leaves the cell, passes along the wire, through the lamp, and back into the cell. Break the loop at any point and everything stops immediately — not just the part beyond the break, but all of it. That is exactly what a switch does: it makes a deliberate gap in the loop. And the same amount of charge that flows into a lamp flows out of the other side. Nothing is consumed on the way.
Voltage is the push, not the stuff
If charge is the thing that flows, what is voltage? Voltage is the push behind the flow, and it is not something that travels along the wire. Water helps here. A pump lifts water to a height; the water then falls and turns a wheel at the bottom. The height is the push. Lift it higher and each litre arrives with more energy, so the wheel does more work. Voltage behaves in the same way: a larger voltage drives the same charge harder, so more energy is delivered where the charge falls through it. The cell does the lifting. The lamp is the wheel at the bottom.
Resistance, and the law that ties it together
Some materials let charge through easily and some fight it. That opposition is called resistance. A thin wire resists more than a thick one, in much the same way that a narrow pipe carries less water than a wide one at the same pressure. Now put the three ideas together, because they are linked by one short rule. More voltage pushes more current through. More resistance lets less current through. Written down, that is Ohm’s law: voltage equals current multiplied by resistance. Knowing any two of the three always gives you the third, which is why it is the first equation anybody learns in electricity.
Curriculum links: NGSS HS-PS3-3