TwiddleLab / Physics / Circuits You Can Build
Voltage: The Push Behind the Flow
What you will learn
- Voltage is the energy each coulomb of charge gets from the battery: 1 volt = 1 joule per coulomb.
- A voltmeter measures the difference between two points (the potential difference). Two points on one wire: 0 V.
- Cells in a row add up: four 1.5 V cells make 6 V. Around a loop, the drops through the lamps add up to the battery's rise.
How the lesson goes
A 9 V battery and a 1.5 V battery. What does the number actually measure?
Voltage is energy per unit of charge: a 9 V battery gives every coulomb 9 joules, a 1.5 V cell gives it 1.5 joules.
Turn the battery until your lamp glows like the green one.
Watch the hill on the right: the battery lifts every coulomb up, the lamp lets it down.
Put the voltmeter probes across the bulb.
The voltmeter shows the difference in energy per coulomb between its two probes.
This push is called voltage.
Voltage is the energy each coulomb of charge carries: 1 volt (V) = 1 joule per coulomb.
A voltmeter compares two points: the potential difference between them. Across a 4.5 V battery: 4.5 V. Across the lamp: the same drop.
Two points on the same bare wire are at the same height: 0 V between them.
Build a 6 V battery from 1.5 V AA cells.
Drop cells into the holders. An empty holder is just a metal strip.
Each cell lifts every coulomb by 1.5 J. Charge passing through four cells in a row is lifted four times: 4 × 1.5 V = 6 V.
Game: Coaster circuit. Shape the track so every lamp gets exactly what it needs.
Drag the yellow handles, then press Ride.
Math: volts are joules per coulomb, a rate like dollars per kilometre. Which battery gives each coulomb the most energy?
Voltage is a rate: energy ÷ charge, V = E ÷ Q, just as a price per km is dollars ÷ km. 18 J ÷ 2 C = 9 V.
Make the voltmeter read 0 V with the probes on two different dots.
A wire has (almost) no resistance, so charges lose no energy along it. Any two points on the same wire are at the same voltage: 0 V apart.
Ride your first coaster on your 6 V battery.
Previous lesson: Current: Charge on the Move · Next lesson: Resistance and Ohm's Law · Part of the course: Circuits You Can Build
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