Question

A parallel-plate capacitor has plates of area 0.40 m² separated by 0.30 mm. The capacitor is connected across a 9.0-V potential source . The energy density in the capacitor is:

a. 6.58x10^-3 J/m3

b. 7.21x10^-5 J/m3

c. 2.67x10^-6 J/m3

d. 1,33x10^-7 J/m3

e. The correct answer is not listed

Answer 1

Let the energy density in the capacitor is u.

Let the electric field in the capacitor plates is E.

The area of the plates A=0.40 m².

The distance between two plates d=0.30 mm.

The voltage across the capacitor V=9.0 V.

The electric field

Now we know energy density in the capacitor

  

  

The answer is (e) The correct answer is not listed.