Peoples Physics Concepts

15.2. Capacitor Energy http://www.ck12.org

Example 1

You have a capacitor with capacitance 100nF. If you connected it to a 12V battery, how much energy is stored in

the capacitor when it is fully charged? If you were to submerge this capacitor in water, how much energy could be

stored in it?

Solution

We’ll just use the equation given above to calculate the energy stored on the capacitor.

Uc=

1

2

CV^2

Uc=

1

2

100 ∗ 10 −^9 F∗12 V

Uc= 6 ∗ 10 −^7 J

By adding a dielectric, we increase the capacitance of the capacitor by a factor of the dielectric constant. The

dielectric constant of water is 80, so the new capacitance will be 80 times the original capacitance.

Uc=

1

2

80 CV^2

Uc=

1

2

80 ∗ 100 ∗ 10 −^9 F∗12 V

Uc= 4. 8 ∗ 10 −^5 J

Watch this Explanation

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/332

MEDIA

Click image to the left for use the URL below.

URL: http://www.ck12.org/flx/render/embeddedobject/333