Capacitor Question?

Question

A parallel plate capacitor has two conductors separated by 10^-7m of insulating silicon dioxide with dielectric constant k=4. Use E_o=10^-11. When the capacitor has .5volts across it each plate has a magnitude 8 x 10^-16 C.

1. How many excess electrons on the plate with the neg charge?

2. What is the value of capacitance?

3. If the plates have a square shape what is the length of their side?

4. What is the electric field inside the insulating layer?

5. How much Energy is stored in the capacitor?

I know these are a lot of questions. I have a problem starting especially when finding the capacitance because in the eqn. for C of a parallel plate capcitor with a dielectric the Area must be known but this is not given. I'm not sure where to start. If someone could please help me with a least knowing where to begin I would greatly appreciate it.

Answer 1

Can you figure out Q1 &4?

Here's the rest.

1. How many excess electrons on the plate with the neg charge?

2. What is the value of capacitance?

q = Cv

q = 8E-16 charge on each plate

v = voltage across the capacitor

C = capacitance

q/v = C

8E-16 / .5 volts = 1.6E-16 Farads (.016 picoFarads)

3. If the plates have a square shape what is the length of their side?

C = €ο * €r * Area / d

C = capacitance

€ο = k = 4

€r = 10^-11

Area = unknown

d = distance between plates in metres

C*d / €ο * €r = Area

1.6E-16Farads * 10^-7m / 4 * 10^-11 = 4E-13^2 metres

sqrt of Area = 6.3245532E-7 / 2 = 3.1622766E-7 metres a side

4. What is the electric field inside the insulating layer?

5. How much Energy is stored in the capacitor?

Energy = 1/2 * v * q

q = 8E-16 charge on each plate

v = voltage across the capacitor

Energy = 2E-16

: )