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

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

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