Ohm's Playground

Why it matters

Georg Ohm spent years heating wires to find one straight line hiding in his numbers. You will find it in sixty seconds.

The idea in plain words

Three letters that run every circuit. Tap them.

V = I × R

A 4 Ω resistor is connected across 12 V. Find the current.

I = 3 A

• volt (V): V — potential difference across the conductor
• ampere (A): I — current through it
• ohm (Ω): R — resistance — the slope of your V–I line
• I = V ÷ R = 12 ÷ 4

Predict first

You double the voltage across a resistor kept at the same temperature. The current…

For a metal at steady temperature, I grows in exact step with V. That straight line through the origin IS Ohm's law: V = I·R.

• doubles — correct
• stays the same — the cell decides the current
• becomes four times

What you do

Plot at least four V–I points for a resistor, then four for the filament bulb. One graph is a ruler-straight line, the other bends — work out why before Decode tells you.

Check yourself

The V–I graph of an ohmic conductor is…

Constant R means I ∝ V — straight, and through zero because no volts, no current.

Why did the bulb's graph bend?

A glowing filament is far hotter than a cold one — hotter metal, higher R, so the current gains less and less.

From a V–I experiment: V = 6 V gives I = 1.5 A. The resistance is…

R = V ÷ I = 6 ÷ 1.5 = 4 Ω.

• a straight line through the origin — correct
• a curve that flattens
• a horizontal line
• The filament heats up, so its resistance rises — correct
• The bulb uses up current as light
• Voltage weakens over time
• 4 Ω — correct
• 9 Ω
• 0.25 Ω