Example from Physics, 18.5 Capacitors and Dielectrics

Capacitor for Camera Flash (part 1)

A typical flash for a point-and-shoot camera uses a capacitor of about $200 μ F$ . (a) If the potential difference between the capacitor plates is 100 V—that is, 100 V is placed “across the capacitor,” how much energy is stored in the capacitor? (b) If the dielectric used in the capacitor were a 0.010-mm-thick sheet of nylon, what would be the surface area of the capacitor plates?

Work it out on paper first. Then open the solution one step at a time, and stop as soon as you can finish on your own.

Strategy for (a)
Given that $V = 100 V$ and $C = 200 \times 10^{−6} F$ , we can use the equation $U_{E} = \frac{1}{2} C V^{2}$ , to find the electric potential energy stored in the capacitor.
Solution
Solution for (a)

Inserting the given quantities into $U_{E} = \frac{1}{2} C V^{2}$ gives

$\begin{matrix} U_{E} & = & \frac{1}{2} C V^{2} \\ = & \frac{1}{2} (200 \times 10^{- 6} F) {(100 V)}^{2} \\ = & 1.0 J . \end{matrix}$
18.44

0 of 2 steps open

How did it go?

Strategy for (a)

Solution

Strategy for (a)

Solution