Volt
The unit of potential difference.
One joule for each coulomb
Work of 6 J moves 2 C of charge from one point of a circuit to another point.
Which statement is right for this pair of points?
What this lesson covers
The idea
The SI unit of potential difference is the volt (V): 1 V is the potential difference when 1 joule of work moves 1 coulomb of charge between two points, so 1 V = 1 J C⁻¹.
One joule for each coulomb
Work of 6 J moves 2 C of charge from one point of a circuit to another point.
Which statement is right for this pair of points?
- Each coulomb needs 3 J of work, so the potential difference is 3 V
- Each coulomb needs 12 J of work, so the potential difference is 12 V
- The potential difference is 6 V, the same as the work
Three examples
Open every tab. Look at how much work is done for each coulomb.
Joules for each coulomb
In every example the potential difference came from dividing the work by the charge. So the unit of potential difference is joule per coulomb, which has its own name.
The SI unit of potential difference is the volt (V). 1 volt is the potential difference between two points when 1 joule of work is done to move 1 coulomb of charge from one point to the other, so 1 V = 1 J C⁻¹.
Notes
The SI unit of potential difference is the volt (V): 1 V is when 1 J of work moves 1 C between two points, so 1 V = 1 J C⁻¹.
Check yourself
What is 1 volt?
Which unit is the same as 1 J C⁻¹?
A charge of 2 C is moved between two points that have a potential difference of 3 V. How much work is done, in J?
Answer: 6 J
Each coulomb needs 3 J, so 2 C need 3 J × 2 = 6 J.
18 J of work is done on a charge across a potential difference of 9 V. How much charge is moved, in C?
Answer: 2 C
Each coulomb needs 9 J, so the charge is 18 J divided by 9 J C⁻¹ = 2 C.
- The current when 1 C of charge flows each second. That describes 1 ampere, the unit of current.
- The potential difference when 1 J of work moves 1 C of charge between two points — correct. Yes!
- The charge carried by 1 J of work. Volt is not a unit of charge. It is a unit of potential difference, work done for each coulomb.
- The ampere. An ampere is 1 C each second, a unit of current.
- The coulomb. A coulomb is a unit of charge, not of work for each unit of charge.
- The volt — correct. Yes!