Coulomb
The unit in which electric charge is counted.
Counting the uncountable
Electrons are far too small to count one by one, so a big unit is used for electric charge. The charge of a single electron is a very tiny part of it.
Roughly how many electrons make up one unit of charge, 1 coulomb?
What this lesson covers
The idea
The SI unit of electric charge is the coulomb (C), equivalent to the charge of nearly 6 × 10¹⁸ electrons; an electron carries a negative charge of 1.6 × 10⁻¹⁹ C.
Counting the uncountable
Electrons are far too small to count one by one, so a big unit is used for electric charge. The charge of a single electron is a very tiny part of it.
Roughly how many electrons make up one unit of charge, 1 coulomb?
- About 6 × 10¹⁸ electrons
- About 6000 electrons
- About 6 × 10⁻¹⁹ electrons
Fill the coulomb boxes
Use the plus button to collect charge. Each box is 1 C.
A huge number of electrons
Each coulomb holds a huge number of electrons, because one electron carries only a tiny charge. Check: 6 × 10¹⁸ electrons times 1.6 × 10⁻¹⁹ C each gives 0.96 C, which is nearly 1 C.
The SI unit of electric charge is the coulomb (C), equivalent to the charge of nearly 6 × 10¹⁸ electrons. An electron carries a negative charge of 1.6 × 10⁻¹⁹ C.
Notes
The SI unit of charge is the coulomb (C), nearly the charge of 6 × 10¹⁸ electrons; one electron carries a negative charge of 1.6 × 10⁻¹⁹ C.
Check yourself
What is the SI unit of electric charge?
About how many electrons are in a charge of 1 C?
What is the charge on one electron?
About how many electrons does a charge of 2 C contain? Give the number in units of 10¹⁸.
Answer: 12 × 10¹⁸
1 C is nearly 6 × 10¹⁸ electrons, so 2 C is nearly 12 × 10¹⁸ electrons.
- The ampere. The ampere is the unit of current, which is the charge flowing each second.
- The joule. The joule is a unit of work done, not of charge.
- The coulomb — correct. Yes!
- Nearly 6 × 10¹⁸ — correct. Yes!
- 1.6 × 10⁻¹⁹. That number is the charge of one electron, in coulombs, not the number of electrons in a coulomb.
- Exactly one. One electron has a charge of only 1.6 × 10⁻¹⁹ C, so a whole coulomb needs a huge number of them.
- Positive, 1.6 × 10⁻¹⁹ C. An electron carries a negative charge.
- Negative, 1.6 × 10⁻¹⁹ C — correct. Yes!
- Negative, 6 × 10¹⁸ C. The number 6 × 10¹⁸ is the number of electrons in a coulomb, not the charge on one electron.