PHY_10_38_V2_P_Capac.energy

LO:
10.3.1.4 – Explain the role of a capacitor in a simple electrical circuit;

What is a capacitor?
What are the main parts of it?
Define capacitance?
What is the formula for the parallel plate capacitor capacitance?
Name the applications of the capacitors?

Activity 2:
Task Read the article on the link

https://www.lifewire.com/what-are-applications-of-capacitors-818986

Application #1:
Short pulse magnets at the National Magnet Laboratory,

106 joules of energy are stored at high voltage in capacitor banks, and released during a period of a few milliseconds. The enormous current produces incredibly high magnetic fields.

Application #2: Quarter shrinker.

Application #3: can crusher.

Some links: shrinking, shrinking (can you spot the physics mistake), can crusher,.
Don’t do this at home. Or this.

Filter Applications
Combined with resistors, capacitors are often used as the main element of frequency selective filters. The available filter designs and topologies are numerous and can be tailored for frequency and performance by selecting the proper component values and quality. Some of the types of filter designs include:

High Pass Filter (HPF)
Low Pass Filter (LPF)
Band Pass Filter (BPF)
Band Stop Filter (BSF)
Notch Filter
All Pass Filter
Equalization Filter

Activity 3: Energy stored in a capacitor
Watch a video and working in a small group or in pairs answer to the questions:

https://www.youtube.com/watch?v=SIU_9SMd5q0

work to charge a capacitor:

move extra charge element dq from one plate to the other
external work required: dW = dq V.

V

+

-

+q

-q

from q=CV

start with zero charge, end up with Q:

capacitor already has charge q, voltage (difference) V

work required to charge the capacitor = change in potential energy

Using Q=CV, three equivalent expressions:

when starting from empty capacitor:

All three equations are valid; use the one most convenient for the problem at hand.

four quantities for a capacitor: C, Q, V, and U
if you know any two of them, you can find the other two

Example: a camera flash unit stores energy in a 150 F capacitor at 200 V. How much electric energy can be stored?

If you keep everything in SI (mks) units, the result is “automatically” in SI units.

12 V, 100 Ah car battery
charge: 3.6x105 C, energy: 4.3x106 J

If batteries store so much more energy, why use capacitors?

100 F capacitor at 12 V
charge: Q=CV= 1.2x10-3 C, energy: U=CV2/2=7.2x10-3 J

we’ll learn how to calculate that later in the course

capacitor stores charge physically, battery stores charge chemically
capacitor can release stored charge and energy much faster

Solve problems

1.A parallel-plate air capacitor has a capacitance of 100 pF with a charge of magnitude 0.1 µC on each plate. The plates are 0.5 mm apart.
(a) What is the potential difference between the plates?
(b) What is the area of each plate?
(c) What is the electric-field magnitude between the plates?
2. A parallel plate capacitor consists of two 5.0 cm x 5.0 cm metal electrodes spaced 1.5 mm apart. The capacitor is connected to a 10 V battery. How much energy is stored in the capacitor?
If students couldn’t finish solve these problems they continue it at home.

Check your understanding