# Magnetic Field at a point between two capacitors

1. Apr 13, 2013

### Renaldo

1. The problem statement, all variables and given/known data

A parallel plate capacitor has circular plates of radius 12.0 cm that are separated by a distance of 4.0 mm. The potential across the capacitor is increased at a constant rate of 1300 V/s. Determine the magnitude of the magnetic field between the plates at a distance r = 3.0 cm from the center.

2. Relevant equations

id = ε0A(dE/dt)

B = [μ0id/(2∏R2)]r

3. The attempt at a solution

id = ε0A(dE/dt)

dE/dt = 1300 V/s
A = ∏R2
R = 0.12 m
ε0 = 8.85E-12

id = 5.2E-10

B = [μ0id/(2∏R2)]r

r = 0.03 m
R = 0.12 m
id = 5.2E-10
μ0 = 1.26E-6

B = 2.17E-16

How do I get there?

2. Apr 13, 2013

### TSny

Note that on the left you have the rate of change of E, but on the right you have the value of the rate of change of V.

[I get an answer that differs from the stated correct answer by a factor of 16.]

3. Apr 14, 2013

### Renaldo

I thought E stood for Vemf. Does it stands for Electric field?

4. Apr 14, 2013

### TSny

E is electric field.