Capacitors Flashcards
What is the primary function of capacitors in circuits?
To store energy for a backup release if power fails.
What are capacitors commonly made of?
Two conductive metal plates with a dielectric between them.
What is the circuit symbol for a capacitor?
Two parallel lines.
What is the definition of capacitance?
Charge stored per unit potential difference between plates.
What is the equation for capacitance?
C = Q / V
What is the unit of capacitance?
Farads (F)
What is the typical range for practical capacitance values?
Microfarads (μF), nanofarads (nF), or picofarads (pF)
In a parallel plate capacitor, what is Q?
Charge on the plates.
What happens to polar molecules in a dielectric when no charge is applied?
They are aligned randomly.
What happens to polar molecules when a charge is applied?
They align with the electric field.
What is permittivity?
A measure of how easily an electric field is generated in a material.
What is relative permittivity (dielectric constant)?
The ratio ε / ε0
What is the equation for permittivity of a material?
ε = εr × ε0
What happens when polar molecules oppose the plate field?
The net field is reduced, increasing capacitance.
What is the equation for capacitance of a parallel plate capacitor?
C = (εr × ε0 × A) / d
What is the formula for area A if the plates are square?
A = L²
What is the definition of dielectric action?
Polar molecules create opposing fields reducing the net field.
What happens to work done as more electrons are added to a charged plate?
More work is needed due to increasing repulsion.
What is the relationship between charge and voltage in a capacitor?
Q is directly proportional to V.
What is the shape of a Q vs V graph?
A straight line through the origin.
What does the area under a Q-V graph represent?
Energy stored in the capacitor.
What is the equation for energy stored in a capacitor?
E = 0.5 × Q × V
What are alternative forms of the energy stored equation?
E = 0.5 × C × V² or E = Q² / (2 × C)
What should you do when asked to draw and explain the charge vs voltage graph?
Draw and explain the graph. The answer is provided in the document.
What happens when a capacitor is connected to a power supply?
Electrons are forced from the positive to the negative plate, charging the capacitor.
What does the capacitor store when connected to a power supply?
Electrical energy on the plates.
What happens when the capacitor is fully charged?
The current in the circuit drops to zero.
How is the charging current initially when the circuit is first connected?
It is at a maximum.
What does the graph of current vs time look like when charging a capacitor?
Draw and explain the graph. The answer is provided in the document.
What does the graph of charge vs time look like when charging a capacitor?
Draw and explain the graph. The answer is provided in the document.
What does the graph of voltage vs time look like when charging a capacitor?
Draw and explain the graph. The answer is provided in the document.
How is energy transferred during capacitor charging?
From electrical energy to electrostatic potential energy on the plates.
What happens when the capacitor is disconnected and connected across a resistor?
The capacitor discharges through the resistor.
What happens to the charge, current, and potential difference during discharge?
They all decrease exponentially.
What does the graph of voltage vs time look like during discharge?
Draw and explain the graph. The answer is provided in the document.
What does the graph of charge vs time look like during discharge?
Draw and explain the graph. The answer is provided in the document.
What does the graph of current vs time look like during discharge?
Draw and explain the graph. The answer is provided in the document.
What is the time constant in capacitor discharge?
The time taken for the charge, current, or voltage to fall to 37% of its original value.
What is the equation for time constant?
τ = RC
What does the symbol τ represent?
The time constant (seconds, s)
What does R represent in τ = RC?
Resistance (ohms, Ω)
What does C represent in τ = RC?
Capacitance (farads, F)
What is the significance of the time constant?
It defines the exponential rate of charging or discharging of a capacitor.
After how many time constants is a capacitor considered fully discharged?
After 5 time constants (5τ)
