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 #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
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
Activity 3: Energy stored in a capacitor Watch a video and working in a small group or in pairs answer to the questions:
Energy Storage in Capacitors work to charge a capacitor : move extra charge element dq from one plate to the other external work required: dW…
Energy Storage in Capacitors
work to charge a capacitor:
move extra charge element dq from one plate to the other external work required: dW = dq V.
start with zero charge, end up with Q:
capacitor already has charge q, voltage (difference) V
Using Q=CV, three equivalent expressions: when starting from empty capacitor:
work required to charge the capacitor = change in potential energy
potential energy stored in capacitor:
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
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.
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
Energy stored in capacitor vs. energy stored in battery
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.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 Assessment
Check your understanding
Tick each criteria or cross it.. - list the various applications of the capacitor; - know the formula of energy stored in a capacitor; - explain the meaning of the formula of energy stored in a capacitor; - apply equations for the energy of the capacitor in solving problems;