The rule that connects them
Show on a big screenMore push. More flow. Does twice the push give twice the flow?
- Axes (the two number lines): push in volts, current in amperes.
- At 1 V the current is 0.2 A.
- At 2 V it is 0.4 A.
- At 3 V it is 0.6 A.
- At 4 V it is 0.8 A.
- At 5 V it is 1.0 A.
- All the points sit on one straight line, through zero.
Drag the push. Then let the wire get warm.
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Twice the push gives twice the current at a fixed temperature.
New word
Resistance — how strongly a part holds current back. Its unit is the ohm (Ω).
The rule
V = IR
V is the push, in volts. I is the current, in amperes. R is the , in ohms. V = IR holds for a metal wire at a fixed temperature.
This is Ohm's law. At a fixed temperature, current is proportional to the push. R stays the same, so V and I climb together. Proportional means twice the push gives twice the current.
For the wire above, 5 V gives 1.0 A. So R = V ÷ I = 5 ÷ 1.0 = 5 Ω. At 2 V the current is 0.4 A. So R = 2 ÷ 0.4 = 5 Ω too. R is the same at every point on the line.
Take a different wire. It has 10 V across it and 2 A through it. Its is R = V ÷ I = 10 ÷ 2 = 5 Ω too.
Watch out!
More push does not always mean more current in the same proportion. That holds only if the temperature stays fixed. A hot metal wire has a higher . So the same push drives less current.
Try the lab to finish this lesson.