Question

In the future, people will only enjoy one sport: Electrodes. In this sport, you gain points when you cause metallic discs hovering on a field to exchange charge. You are an Electro Disc player playing the popular four disc variant. The disks have charges of qA = −8.0 µC, qB = −2.0 µC, qC = +5.0 µC, and qD = +12.0 µC. (a) You bring two disks together and then separate them. You measure the resulting charge of these two disks and find that it is +8.5 µC per disk. Which two disks did you bring together

Answer 1

• Disk C and Disk D

Step-by-step explanation:

The total charge in the disks

`q_1 + q_2 = q_(total)`

must be conserved before and after bringing them together.

Lets equate the sum of the initial charge with the sum of the final for the disk:

`q_(1_i) + q_(2_i) = q_(1_f) + q_(2_f) = 2 * (+8.5) \mu C`

`q_(1_i) + q_(2_i) = +17 \mu C`

So, the initial charges must sum +17 μC.

Now, as there are no charges over +17 μC, this means that both charges must be positive.

As the only positive charges are
`q_C` and
`q_D`, this disk must be the ones we are looking for. And, as we can see, they sum 17 μC:

`q_(C) + q_(D) = 5 \mu C + 12 \mu C = 17 \mu C`