What does the voltage between two points of a circuit state?
Every circuit so far has a battery in it. Take the battery out, and nothing flows. What exactly does the battery do? And what runs out when it dies?
In earlier grades you saw energy changing form: chemical energy becoming light, motion, or heat. The battery is where a circuit's energy story starts.
A battery holds a store of chemical energy.
Each coulomb of charge that passes through the battery is given some of that energy: the battery transfers chemical energy to each coulomb.
The component that gives energy to the charge passing through it is called the source of the circuit.
A battery is a source. A power supply, a plug-in box doing the same job, is a source too.
How much energy per coulomb does the source give? That is its voltage: a 9 V battery gives each coulomb 9 J.
The source sets the voltage, and that voltage drives the current around the loop.
Which job does the source of a circuit do?
One correction is worth making now: a battery does not drive one fixed current wherever it is used.
Connect different components across the same 9 V battery, and different currents flow. But the battery still gives each coulomb 9 J.
A battery drives a current through a music player's motor. Which energy transfer happens inside the battery?
Write down the facts:
A battery holds chemical energy.
Each coulomb passing through the battery is given some of that energy.
Inside the battery, chemical energy is transferred to each coulomb of charge passing through.
A battery drives a current through a camping lantern. Which energy transfer happens inside the battery?
The same 6 V battery is connected first to a small heater, then to a toy siren. What does the battery hold the same in both circuits, and what may differ?
Write down the rule:
The source sets the voltage: 6 V means 6 J given to each coulomb, in both circuits.
The current is not fixed by the battery. It depends on the circuit connected.
The battery gives each coulomb 6 J in both circuits; the two currents may differ.
The same battery is connected first to one component, then to a different one. What stays the same?
And the dead battery? Its store of chemical energy is used up. That is what runs out.
A fresh 6 V battery is connected to a small heater, and later to a toy siren. Which statement is correct?
What runs low as a battery is used?
Jonah says a battery always pushes out the same current, whatever is connected to it. What does a battery actually fix?