Capacitors

Question 1

What is the primary function of capacitors in circuits?

Answer 1

To store energy for a backup release if power fails.

Question 2

What are capacitors commonly made of?

Answer 2

Two conductive metal plates with a dielectric between them.

Question 3

What is the circuit symbol for a capacitor?

Answer 3

Two parallel lines.

Question 4

What is the definition of capacitance?

Answer 4

Charge stored per unit potential difference between plates.

Question 5

What is the equation for capacitance?

Answer 5

C = Q / V

Question 6

What is the unit of capacitance?

Answer 6

Farads (F)

Question 7

What is the typical range for practical capacitance values?

Answer 7

Microfarads (μF), nanofarads (nF), or picofarads (pF)

Question 8

In a parallel plate capacitor, what is Q?

Answer 8

Charge on the plates.

Question 9

What happens to polar molecules in a dielectric when no charge is applied?

Answer 9

They are aligned randomly.

Question 10

What happens to polar molecules when a charge is applied?

Answer 10

They align with the electric field.

Question 11

What is permittivity?

Answer 11

A measure of how easily an electric field is generated in a material.

Question 12

What is relative permittivity (dielectric constant)?

Answer 12

The ratio ε / ε0

Question 13

What is the equation for permittivity of a material?

Answer 13

ε = εr × ε0

Question 14

What happens when polar molecules oppose the plate field?

Answer 14

The net field is reduced, increasing capacitance.

Question 15

What is the equation for capacitance of a parallel plate capacitor?

Answer 15

C = (εr × ε0 × A) / d

Question 16

What is the formula for area A if the plates are square?

Answer 16

A = L²

Question 17

What is the definition of dielectric action?

Answer 17

Polar molecules create opposing fields reducing the net field.

Question 18

What happens to work done as more electrons are added to a charged plate?

Answer 18

More work is needed due to increasing repulsion.

Question 19

What is the relationship between charge and voltage in a capacitor?

Answer 19

Q is directly proportional to V.

Question 20

What is the shape of a Q vs V graph?

Answer 20

A straight line through the origin.

Question 21

What does the area under a Q-V graph represent?

Answer 21

Energy stored in the capacitor.

Question 22

What is the equation for energy stored in a capacitor?

Answer 22

E = 0.5 × Q × V

Question 23

What are alternative forms of the energy stored equation?

Answer 23

E = 0.5 × C × V² or E = Q² / (2 × C)

Question 24

What should you do when asked to draw and explain the charge vs voltage graph?

Answer 24

Draw and explain the graph. The answer is provided in the document.

Question 25

What happens when a capacitor is connected to a power supply?

Answer 25

Electrons are forced from the positive to the negative plate, charging the capacitor.

Question 26

What does the capacitor store when connected to a power supply?

Answer 26

Electrical energy on the plates.

Question 27

What happens when the capacitor is fully charged?

Answer 27

The current in the circuit drops to zero.

Question 28

How is the charging current initially when the circuit is first connected?

Answer 28

It is at a maximum.

Question 29

What does the graph of current vs time look like when charging a capacitor?

Answer 29

Draw and explain the graph. The answer is provided in the document.

Question 30

What does the graph of charge vs time look like when charging a capacitor?

Answer 30

Draw and explain the graph. The answer is provided in the document.

Question 31

What does the graph of voltage vs time look like when charging a capacitor?

Answer 31

Draw and explain the graph. The answer is provided in the document.

Question 32

How is energy transferred during capacitor charging?

Answer 32

From electrical energy to electrostatic potential energy on the plates.

Question 33

What happens when the capacitor is disconnected and connected across a resistor?

Answer 33

The capacitor discharges through the resistor.

Question 34

What happens to the charge, current, and potential difference during discharge?

Answer 34

They all decrease exponentially.

Question 35

What does the graph of voltage vs time look like during discharge?

Answer 35

Draw and explain the graph. The answer is provided in the document.

Question 36

What does the graph of charge vs time look like during discharge?

Answer 36

Draw and explain the graph. The answer is provided in the document.

Question 37

What does the graph of current vs time look like during discharge?

Answer 37

Draw and explain the graph. The answer is provided in the document.

Question 38

What is the time constant in capacitor discharge?

Answer 38

The time taken for the charge, current, or voltage to fall to 37% of its original value.

Question 39

What is the equation for time constant?

Answer 39

τ = RC

Question 40

What does the symbol τ represent?

Answer 40

The time constant (seconds, s)

Question 41

What does R represent in τ = RC?

Answer 41

Resistance (ohms, Ω)

Question 42

What does C represent in τ = RC?

Answer 42

Capacitance (farads, F)

Question 43

What is the significance of the time constant?

Answer 43

It defines the exponential rate of charging or discharging of a capacitor.

Question 44

After how many time constants is a capacitor considered fully discharged?

Answer 44

After 5 time constants (5τ)