A-level Physics (Advancing Physics)/Charge/Worked Solutions

1. How much charge do 1234 electrons carry?

1234 x 1.6 x 10⁻¹⁹ = 1.9744 x 10⁻¹⁶ C = 197.44 aC (attocoulombs)

2. How many electrons does is take to carry 5 C of charge?

5 = 1.6 x 10⁻¹⁹ x n

$n={\frac {5}{1.6\times 10^{-19}}}=3.125\times 10^{19}{\mbox{ electrons}}$

3. The total charge on 1 mole of electrons (6 x 10²³ particles) is equal to 1 faraday of charge. How many coulombs of charge are equal to 1 faraday?

1 faraday = 6 x 10²³ x 1.6 x 10⁻¹⁹ coulombs = 96000 coulombs =96kC

4. The mass of a ball is 50 mg. It is supplied 5C of charge. Will there be any change in the mass of the ball? If so, calculate the change of the mass.

5 = 1.6 x 10⁻¹⁹ x n

$n={\frac {5}{1.6\times 10^{-19}}}=3.125\times 10^{19}{\mbox{ electrons}}$

$3.125\times 10^{19}{\mbox{ electrons}}\times {9.11\times 10^{-31}}{\mbox{ kg/electron}}=2.84\times 10^{-11}{\mbox{ kg}}$