How Does Doubling Charge Affect Electric Field Strength in a Capacitor?

[phyBnewb]

Homework Statement

A parallel-plate capacitor consists of two square plates, size L x L, separated by distance d. The plates are given charge +-Q . Each part changes only one quantity; the other quantities have their initial values.

Part A

What is the ratio E(final)/E(initial) of the final to initial electric field strengths if Q is doubled?

Homework Equations

I know that:E = kQ/r^2 ,where k= 8.99*10^9

The Attempt at a Solution

I am not sure where to start here for this question.
Since it is a ratio of E final / E initial would Q cause E to be something like this?
E = k(2Q)/r^2 => 1/2E for E final?

 

[phyBnewb]

I tried 1/2 but it was incorrect. Help please!

 

[nasu]

You are using the formula for a point charge in the case of a parallel plate capacitor.
The electric field inside the capacitor is constant and is given by E=V/d where V is the voltage and d is the distance between the plates.

 

[phyBnewb]

i figured it out. it wasnt 1/2, for Efinal/Einitial = 2