Calculating the number of electrons

When calculating the number of electrons, you’re really calculating the charge (because charge is just a multiple of the number of electrons).

Charge of a single electron

The charge of a single electron is about -1.60\times 10^{-19} coulombs.

Similarly a coulomb has the same charge as 6.25\times 10^{18} electrons.

Equation for the number of electrons in a charge

n=\frac Qe

Where:

• n is the number of electrons
• Q is the total charge in coulombs
• e is the charge of a single electron (1.60\times 10^{-19}C)

Example: if 0.032C flows into a motoro in 0.20s, calculate the current flow

• Q=It
• 0.032C=I\times 0.20s
• I=\frac{0.032C}{0.20s}
• I=0.16A

Estimate the number of electrons flowing in 20s if a current of 25mA flows

• I=25mA=0.025A
• t=20s
• Q=It
• Q=0.025A\times 20s
• Q=0.50C
• n=\frac Qe
• n=\frac{0.50C}{1.60\times 10^{-19}C}
• n=3.1\times 10^{18} electrons

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