Question

A 100 pF capacitor has circular plates of 10.0 cm radius that are 5.0 mm apart and have air beteween them. The capacitor is charged by connecting it to a 12.0 V battery through a 1.0 ohms resistor.

a) Determine the current through the plates at t = 0 (when the battery is connected)

b) Determine the current through the plates at t = 60s?

c) Determine the rate at which the electric field between the plates changes at t= 0 and t = 60s

d) Determine the magnetic field between the plates at t = 0 and at t = 60s

Don't really care about the answers as much, but more about what formulas are being used.

Thanks!

Answer 1

regarding RC circuit, we have following formulas that we usually need

1. quation for charge while charging in RC ckt is Q = Q0(1-e^-t/T)
where T = timeconstant = RC
Q0 = initail charge = CV

2.equation for charge while discharging in RC ckt is Q = Q0(e^-t/T)
where T = timeconstant = RC
Q0 = initail charge = CV

3. equation for current while charging/discharging in RC circuit is gievn by
i = i0(e^-t/T)
where T = timeconstant = RC
io = initail current = v/R =

4. equation for volatge in RC ckt while charging is V= V0(1-e^-t/RC)

5. equation for volatge in RC ckt while discharging is V= V0(e^-t/RC)

also with respect to RC ckt

Capacitance C of a parallel palte capacitor is given by C = KeoA/d
where A = area = pi r^2,

e0 = constnat = 8.85*10^-12,
d   = distance between the plates,

K = dieelctric constant (=1 for air)  

Chareg Q = CV where V = Volatge

Energy U = 0.5QV = 0.5 CV^2 = Q^2/2C

eletric field E = V/d

now try urself to solve problem,