Electronics II Flashcards
Descriptions, formulas and units
Direct Current (DC)
An electric current flowing in one direction only.
Alternating Current (AC)
An electric current that flows in either direction.
Electric current
The flow of electric charge.
Electric current equation
I = V / R
or
I = ΔQ / Δt
Electric current units
Amperes (A)
Potential difference (voltage)
The difference of electrical potential between two points of a component.
Potential difference equation
V = I R
or
V = W / Q
Potential difference units
Volts (V)
Electrical resistance
A measure of the difficulty to pass current through a conductor.
Electrical resistance equation
R = V / I
Electrical resistance units
Ohms (Ω)
Resistors in series
When resistors are connected in series, the current through each resistor is the same.
Resistors in series equations
R = R1 + R2 + R3…….
Resistors in parallel
The total current through the resistors in parallel, is equal to the sum of the individual currents.
Resistors in parallel equation
1/R = 1/R1 + 1/R2 + 1/R3…….
Resistivity
A measure of the resisting power of a specified material to the flow of an electric current.
Resistivity equation
ρ = R A / L
Resistivity units
Ohm-metre (Ωm)
Electrical power
The rate, per unit time, at which electrical energy is transferred by an electric circuit.
Electrical power equation
P = V I or P = I^2 R or P = V^2 / R
Electrical power units
Watts (W)
Equation of a complete circuit
ε = I R + I r or ε = V + I r or ε = V + v
Capactience
The ability of a system to store an electric charge.
Capactience equation
C = Q V
Capactience units
Farad (F)
Energy stored equations
W = ½ Q V or W = ½ CV^2 or W = ½ Q^2 / C
Capacitor discharge equations
V = Vo e^ – t / RC or I = Io e^ – t / RC or Q = Qo e^ – t / RC
Time constant
This is the time taken for the capacitor to discharge to 0.37 of its initial charge.
Time constant equation
time constant = RC
Potential divider
Consists of two or more resistors connected in series across a source of fixed potential difference.