Studied by 12 people
Physics 3.6 - Electrical Systems
Ampere (A)
SI unit for current
Ohm (\Omega)
SI unit for resistance, reactance, impedance
Volt (V)
SI unit for voltage/potential difference
Watt (W)
SI unit for power
Farad (F)
SI unit for capacitance
Henry (H)
SI unit for inductance
Metre (m)
SI unit for distance
Weber (Wb)
SI unit for magnetic flux
Tesla (T)
SI unit for magnetic field strength
Radians (rad)
Units for phase angle. One complete cycle is 2\pi rad
Charge
Eletricity stored in an object due to an imbalance of protons or electrons, creating a force that can be discharges through a conductor
Combination circuit
A circuit containing both series and parallel elements
Current
Flow of electric charge
EMF (Electromotive force)
The force that pushes charges through a circuit
Equivalent resistance
The single resistance value that could replace multiple resistors while maintaining the same current
Internal resistance
Opposition to the flow of current within a battery or power source
Junction
A point where 3 or more conductors meet
Kirchhoff’s current law
The total current entering a junction is equal to the current leaving a junction
Loop
A closed path followed by the current in a circuit
Kirchhoff’s voltage law
In a closed loop, the total voltage is equal to the sum of the voltage drops
Resistance
Opposition to current flow
Ohm’s Law
V=IR
Parallel circuit
A circuit with more than one pathway for current to flow
Power
The rate at which energy is transferred
Series circuit
Circuit with only one way for current to flow
Voltage
The electrical potential difference between two points
Terminal voltage
The potential difference between two terminals of a power source, accounting for internal resistance. V_T=\epsilon-Ir
Capacitance
Ability to store an electric charge between two conducting plates separated by an insulator
Adding capacitance in a parallel capacitor network
Sum of individual capacitances. C_T=C_1+C_2…
Adding capacitance in a series capacitor network
Sum of inverse individual capacitances. \frac{1}{C_T}=\frac{1}{C_1}+\frac{1}{C_2}…
Capacitor construction equation
C=\frac{\epsilon_0\epsilon_rA}{d}
Charge in a series capacitor network
The same across all capacitors - based on voltage applied and equivalent capacitance across the network (C=\frac{Q}{V})
Charge in a parallel capacitor network
Divided among capacitors based on capacitance (higher capacitance stores more charge). Q_T=Q_1+Q_2…
Combination capacitor network
Network containing both series and parallel elements
Dielectric constant
Property of insulating materials measuring ability to store electrical energy in an electric field.
Electrical field
Region around a charged object which exerts a force on other charged objects
Electric field lines
Point from positive to negative
Overlapping area
Where electric field lines from different objects intersect, influencing electric potential
Permittivity of free space (\epsilon_0)
8.85Ă—10^{-12}F\space{m}^{-1}. Represents ability of a vacuum to permit electric field lines
RC circuit
A circuit with a capacitor and resistor
Time constant (RC circuit)
Time for a capacitor to charge or discharge 63% of its total amount
Voltage in a parallel capacitor network
Voltage in a series capacitor network
Each capacitor has a different voltage, based on capacitance. V_T=V_1+V_2…
Eddy currents
Swirling groups of electrical current induced in conductors by changing magnetic fields that create resistance
Induction
Process of generating EMF in a closed circuit by changing the magnetic field through the circuit
Faraday’s Law
The size on an induced EMF is proportional to the negative rate of change of the magnetic flux
Inductance
Property of an abject that opposes change in electric current and stores energy in a magnetic field
Isolating transformer
Device that transfers electrical energy between circuits using induction while providng electrical isolation
Lenz’s Law
Direction of induced current opposes the change that created it (negative sign in Faraday’s law)
Magnetic flux
Measure of magnetic field lines passing through a surface
Primary windings
Coils of a transformer where input voltage is applied
Secondary windings
Coils of a transformer where induced voltage is transferred to
RL circuit
Circuit containing an inductor and a resistor
Self-induction
A changing current in a coil induces an EMF that opposes the change in current
Time constant (RL circuits)
Time taken for the current to reach 63% of its total or reduce by 37%
Step-up transformer
Increases voltage by decreasing current
Step-down transformer
Decreases voltage by increasing current
Angular frequency
The frequency of a steadily recurring phenomenon
Average power
Equivalent to DC power, half of maximum power
Capacitive reactance (X_C)
How much a capacitor impedes the current in a circuit
Inductive reactance (X_L)
How much an inductor impedes the current in a circuit
Frequency
The rate at which something occurs over a period of time
Impedance
The effective resistance of a circuit or component to current from the combined effects of resistance and reactance
Instantaneous voltage/current
The voltage/current at a particular time
In phase
When 2 or more waves with the same frequency reach minimum and maximum at the same time
Leading
Before or in front of
Lagging
Following behind
Period
Time for one oscillation
Phase angle
A phase difference e
Phasor
A line used to represent an electrical quantity as a vector
Resonance
Increase in amplitude of oscillation of asystem exposed to a force equal to or very close to the system’s natural (resonant) frequency
Resonant frequency (f_o)
The natural frequency of a system
V_L ____ V_R by ÂĽ cycle
leads
V_C ____ V_R by ÂĽ cycle
lags
Current is zero when
V_C=V_S
Note 
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