How much energy is stored by the electric field between two square plates, 8.1 cm on a side, separated by a 1.9-mm air gap? The charges on the plates are equal and opposite and of magnitude 17 nC . Express your answer using two significant figures and include the appropriate units.

4.66×10^-6J

Explanation:

The capacitance of a capacitor is given by:

C= ε A/d

ε= permittivity of free space

A= Area of the plates

d= distance between the plates.

A= (8.1×10-2)^2= 65.61×10^-4m2

d= 1.9× 10^-3m

ε= 8.85×10^-12

C= 8.85×10^-12 × 65.61×10^-4/1.9× 10^-3

C= 3.1×10^-11 F

Energy stored in a capacitor= q^2/2C

But q= 17×10-9

E= (17×10^-9)^2/2×3.1×10^-11

E= 4.66×10^-6J

0.11 m/s and 0.28 m/s should be correct