Electrical Systems - Definitions - Level 3 Flashcards
Alternating current (A.C.)
An electric current that first moves in one direction, then moves in the opposite direction with a regular frequency.
Ammeter
A device that measures current when connected in series in a circuit.
Capacitance
The amount of charge a capacitor can store when connected across a potential difference of 1 volt (larger capacitance means capacitor can store more charge for each volt).
Capacitor
A device that can store electric charge (and energy) and then release it at some later time, being made from two parallel oppositely charged plates.
Charging
When a capacitor gains a charge, causing a potential difference across its plates.
Conductors
Materials that allow electric charges to flow through them easily.
Conventional current
Current flowing from the positive to negative terminal of a cell.
Electric current and size
The flow of electricity through a conductor.
The size of a current is the amount of charge flowing per second past a point.
Current Electricity
The continuous flow of electrons through a conductor.
Dielectric constant (Ɛr)
The proportion by which the capacitance increases when a dielectric insulator is placed between the plates of a capacitor.
Direct current (D.C.)
An electrical current that always moves in one direction.
Discharging
When a capacitor loses a charge causing a potential difference across its plates.
Electric current
The flow of electric charge.
Electric field
The field around charged particles that exerts a force on other charged particles.
Electric field lines
A map of an electric field representing the direction of the force that a positive charge would experience.
Electric flux
The product of a surface area and the component of the electric field perpendicular to the surface.
Electric generator
A mechanical device that uses wire loops rotating inside a magnetic field to generate electricity.
Electric potential
The difference in electrical charge between two points in a circuit, (potential difference).
Electric potential energy
The potential energy of a charge due to the position of the charge near other charges.
Electrical energy
A form of energy from electromagnetic interactions.
Electrical force
A fundamental force that results from the interaction of electrical charge.
Electrical insulators
Materials that obstruct the flow of electrical current.
Electrical resistance
The property of opposing electric current.
Electromagnet
A magnet formed by a solenoid that can be turned on and off by turning the current on and off.
Electromagnetic force
The force of attraction or repulsion between two charged particles (one of the four fundamental forces).
Electromagnetic induction
Mechanical energy is converted to electrical energy by moving a loop of wire in a magnetic field or by changing the magnetic field. This results in an induced voltage which can cause a current if the circuit is complete.
EMF (ℰ)
The potential difference across the terminals of a cell when no current is flowing from it.
Electron current
Opposite to conventional current; electron current flows from the negative terminal to the positive terminal.
Faraday’s law of mutual induction
The rate of change in magnetic flux in a coil is directly proportional to the induced voltage.
Impedance
Combination of resistance and reactance in an AC circuit.
Induced voltage
Voltage created by the combination of movement and a magnetic field.
Inductance
The effect in a circuit when a changing current causes an opposing induced voltage.
Induction
Conversion of kinetic energy to electrical energy using a magnetic field.
Inductor
A device that produces an opposing voltage when the current/magnetic field changes.
- An ideal inductor is one in which the resistance is negligible
- Inductors are mainly used in circuits carrying AC
Insulators
Materials that are poor conductors of electricity.
Diode
A resistor which allows current to flow in one direction only. An inital smaller voltage is required before a current can pass through a diode, thus current does not flow initially as there is greater resistance until voltage reaches 0.6V. Diodes act as non-ohmic resistors.
Internal resistance
The resistance of chemicals inside the power supply.
Terminal voltage (Vr)
A measure of the energy supplied to the source minus the energy used by each coulomb of charge flowing through it.
Vterminal = EMF - Voltage across internal resistor
/
Vterminal = EMF − IR
Mutual inductance
Mutual inductance occurs when the current changes in the primary coil (P), and it creates a changing magnetic field which passes through the secondary coil (S). The changing magnetic field induces a voltage and a current in the secondary coil (S).
Transformer
A transformer consists of two coils wound into an iron core to produce an induced voltage and current.
- Transforms the voltage in an AC circuit
Step-up transformer
If there are more turns in the secondary coil than the primary coil, the transformer can make Vs greater than Vp.
Vp < Vs
Np < Ns
Where,
Ns is the number. of turns in the secondary coil
Np is the number. of turns in the primary coil
Vs is the voltage across the secondary coil
Vp is the voltage across the primary coil
Step-down transformer
If there are more turns in the primary coil than the secondary coil, the transformer can make Vp greater than Vs.
Vp > Vs
Np > Ns
Where,
Ns is the number. of turns in the secondary coil
Np is the number. of turns in the primary coil
Vs is the voltage across the secondary coil
Vp is the voltage across the primary coil
Right hand slap rule for current-carrying wire (Motor rule)
Used when a current-carrying wire is placed in a magnetic field to find the direction that the magnetic force acts in.
B - Fingers are in the direction of the magnetic field lines
I - Thumb is in the direction of the current
F - Palm is in the direction the magnetic force acts in
Right hand slap rule for single charged particle (Motor rule)
Used when a single charged particle moves through a magnetic field to find the direction that the magnetic force acts in.
B - Fingers are in the direction of the magnetic field lines
I - Thumb is in the direction of the particle’s velocity
F - Palm is in the direction the magnetic force acts in
NOTE - When a positively charged particle travels through a magnetic field, thumb points in the same direction that the particle is travelling.
When a negatively charged particle travels through a magnetic field, thumb points in the opposite direction to the particle’s motion.
Lenz law
An induced current causes a force to oppose the change which produced it (work is done to produce electrical energy).
Magnetic dipole
Magnet with two poles (north and south), all magnets are made up of dipoles.
Magnetic flux
The lines of force surrounding a permanent magnet or a moving charged particle.
Magnetic flux density
Amount of flux density in a fixed area.
Magnetic flux energy
The total magnetic field energy passing through a given area.
Kirchhoff’s law of circuits - Current law
The total current entering a junction in a circuit is equal to the total current leaving.
Kirchhoff’s law of circuits - Voltage law
In a closed-loop of a circuit, the algebraic sum of emf’s of cells is equal to the algebraic sum of IR products of all the resistors.
or
The algebraic sum of all the emf voltages of cells is equal to zero.
Magnetic poles
The ends or sides of a magnet about which the force of magnetic attraction seems to be concentrated.
Magnetic reversal
The flipping of polarity of the earth’s magnetic field.
Permittivity
Proportion by which the capacitance increases when an insulator is placed between the plates of a capacitor.
Potential difference
The difference in voltage between two points
Reactance
The ability of a capacitor or inductor to limit the current in an A.C. circuit
Power
The rate at which energy is transformed/work is done
Resistance
The opposition of a conductor to the flow of electric current, when connected to a voltage supply.
Resistors
Objects that allow charge to flow at a reduced rate (changed into heat or light)
Secondary coil
Coil of wire in which the voltage in the primary coil is stepped up or down by way of electromagnetic induction.
Solenoid
A cylindrical coil of wire that becomes electromagnetic when a current runs through it.
Sources of EMF
A battery, generators, or solar cells are sources of EMF.
Simple circuit
A circuit that has only one pathway for electricity to flow through.
Superconductors
Materials in which, under certain conditions, the electrical resistance approaches zero.
Time constant
The time taken for the voltage or current to change by 63% of the existing value.
Uniform electric field
An electric field of constant strength when the field lines are parallel and equally spaces.
Voltage drop
The electric potential difference across a resistor or other part of a circuit that consumes power.
Voltage/current characteristics
The graphical representation of voltage against current for a particular component.
Efficiency
Efficiency is the ratio of energy output to energy input expressed as a percentage.
Self-inductance
Self-inductance occurs when a coil is connected to a power supply and the switch is closed, as it will take time for the current to build up from zero to its steady value.
- While the current is increasing, there will be a changing magnetic flux in the coil which will cause a voltage to be induced against the applied voltage. This induced voltage will oppose the increasing current, slowing the build-up of current in the coil (and vice versa - see lenz law).
Half-life of a capacitor
Half-life is the time taken for the capacitor to discharge its charge by half
Dielectric effect
The dielectric effects results when insulating material is placed between the parallel plates of a capacitor, causing the capacitance to increase. The dielectric insulation allows more charge to be stored.
Voltage
Voltage is a measure of the work done or change in energy on each coulomb of charge as it moves between two points.
Modified right hand slap rule
Used when a loop of wire is moved through a magnetic field to find the direction of the induced current
B - Fingers are in the direction of the magnetic field lines
v - Thumb is in the direction of the movement
F - Palm is in the direction the induced current
Isolating transformer to protect against electric shock
If there are more turns in the secondary coil than the primary coil, the transformer can make Vs greater than Vp.
Vp = Vs Np = Ns
Where,
Ns is the number. of turns in the secondary coil
Np is the number. of turns in the primary coil
Vs is the voltage across the secondary coil
Vp is the voltage across the primary coil
