Physics help

I have a LOT of physics homework. if some smart people can help me that will be amazing, as I am not that good at physics.
it is higher physics and the unit is Electricity.

first question:
1a) A 50microfarad is charged until the p.d. across it is 100V. Calculate the charge on the capacitor when the p.d. across it is 100V.

I got 5x10^-3 C.

1b) the capacitor is now fully discharged in a time of 4 milliseconds. Calculate the avg current during this time. Why is this avg current?
how to do part b?

Reply 1

Joinedup

20

Original post by dude101010

I have a LOT of physics homework. if some smart people can help me that will be amazing, as I am not that good at physics.
it is higher physics and the unit is Electricity.

first question:
1a) A 50microfarad is charged until the p.d. across it is 100V. Calculate the charge on the capacitor when the p.d. across it is 100V.

I got 5x10^-3 C.

1b) the capacitor is now fully discharged in a time of 4 milliseconds. Calculate the avg current during this time. Why is this avg current?
how to do part b?

Current is measured in Amps and one Amp is defined as a Coulomb per second

for the average current you want to divide the quantity of charge by the time taken for it to flow (in seconds)... so quite similar to the calculation you'd do to find the average speed of a car that travelled 40 miles in one hour.

pretty sure that's all they'll be expecting.

Reply 2

dude101010

OP

13

thanks, mate. :smile:

Reply 3

dude101010

OP

13

wait, why is it average current?

Reply 4

uberteknik

21

Original post by dude101010

wait, why is it average current?

The actual current follows a logarithmic decay curve not a straight line. i.e.
The instantaneous current at any time during the discharge, is not the same.