Capacitors, Magnetism and Inductance

Question 1

How does a capacitor work?

Answer 1

Temporarily stores charge between two oppositely charged plates separated by an insulator (di-electric)

Question 2

What are 3 applications of capacitors?

Answer 2

• Energy storage: Can store up charge slowly and discharge suddenly (ignition systems)
• DC blocking/ AC passing: By placing in series, can block DC and pass AC
• Resonant Circuits: Radio circuits are based of a circuit containing a capacitor and an inductor. Current flowing through converts between voltage and current (like a pendulum with kinetic/potential energy).

Question 3

What happens to the charge when a capacitor is connected to a DC supply?

Answer 3

• The EMF supplies an opposite charge to the plate, which creates an attracting field in the dielectric.
• This charge in the plates elongates the electron shells. The electrons are attracted to the ‘+’ plate and the protons are attracted to the ‘-‘ plate.
• The elastic nature of the elongated shells stores energy and releases it once EMF is removed.

Question 4

What is the Di-electric constant?

Answer 4

‘K’
- The ability of a material to support an electric field. Proportional to the amount of charge it can hold.
- Common di-electrics = Air, Paper, Tantalum

Question 5

What is the Di-electric Strength?

Answer 5

The ability of a material to prevent significant current with EMF
-OR-
The highest voltage it can withstand before breakdown of material.

Question 6

What is the unit for capacitence?

Answer 6

Farad

Question 7

What is the equation for calculating capacitance on a standard capacitor and multiple plate capacitor?

Answer 7

C=(kA) / d Standard capacitor
C= (kA (N-1) / d Multiple plate capacitor

Question 8

What characteristic does capacitors wired in parallel have?

Answer 8

They act like a single capacitor with increased area. Because they are in parallel, the voltage is the same.
- Ct = C1+C2+C3……

Question 9

What characteristic does capacitors wired in series have?

Answer 9

The total capacitance is smaller than the smallest capacitance value. Because they are wired in series, the sum of the voltage drops will equal the EMF.
(1/Ct) = (1/C1) + (1/C2) + (1/C3) ……