Gaps in knowledge - Capacitor theory

Question 1

What is the Di-electric constant?

Answer 1

Ability to support an electric field
- Proportional to the amount of charge it can hold.

Question 2

What is the di-electric strenght of a matieral?

Answer 2

Ability to prevent significant current when EMF is applied
- OR highest voltage it can withstand before breakdown.

Question 3

What is the unit of capacitance?

Answer 3

Farads
- C = (kA (N-1)) / d

Question 4

What is a Varactor diode?

Answer 4

A variable capacitor that changed capacitance when voltage is applied.
- made from semiconductor

Question 5

What does the working voltage of a capacitor indicate?

Answer 5

Di-electric strength
- Should be 50% higher than the highest value
- DC RATING

Question 6

What is the voltage rating used for capacitors in AC?

Answer 6

Peak Voltage.

Question 7

What is the equation for charge in a capacitor?

Answer 7

Q=CV
- Capacitance is determined by charge stored and applied EMF

Question 8

What is an characteristics of using ceramic capacitors?

Answer 8

• High voltage, low capacitance.

Question 9

What is a Mica capacitor?

Answer 9

Ceramic
- Small capacitance, high voltage
- Thin sheets of mica between metal sheets.

Question 10

What is a Paper capacitor?

Answer 10

Ceramic
- Thin conductive foils separated by paper enclosed in a metal can.
- For HIGH VOLTAGE: - Filled with oil to fill any high voltage breakdown points in paper.

Question 11

What are the characteristics of an aluminium electrolytic capacitor?

Answer 11

Positive - aluminium foil
Negative - electrolyte plate
- Negative = DIRECTLY ATTACHED TO CASE
VERY HIGH CAPACITANCE, low working voltage

Question 12

What are characteristics of Tantalum capacitors?

Answer 12

Electrolytic
- Similar to aluminium, but longer shelf life, lower leakage current and higher capacitance.

Question 13

What is the equation for time constant of capacitors?

Answer 13

T = CR

Question 14

What is the charge % after 1-5 Time constants?

Answer 14

63.2%, 86.5%, 95%, 98%, 100%

Question 15

Application of time constants in circuit?

Answer 15

To design a circuit that provides a known time delay.

Question 16

Why are open circuits in capacitors difficult to detect?

Answer 16

A lead detaching from a package can show high resistance (indicating serviceable)
- Use test equipment to measure capacitance
- OR use AC supply for NON-ELECTROLYTIC capacitors to check if AC current flows.