NCEA Level 3 Electricity

A.C.

Alternating Current

Alternating current

An electric current that first moves one direction, then the opposite direction with a regular frequency

Ammeter

Device that measures current when connected in series in a circuit

Ampere

The rate of flow of charge per second

Ampere (Amp)

Unit of electric current. It is equivalent to coulomb/sec.

Attraction of Electric Charges

Unlike charges give negative potential energy (attractive force). Unlike charges attract one another.

Capacitance

Measure of a capacitor's ability to store charge, calculated by the ratio of the magnitude of charge on one plate to the voltage across the two plates, expressed in SI units, farads.

Capacitators

Stores electrical energy as an electric field.

Capacitor

Device that stores electric charge on two oppositely charged plates

Cell

Positive to negative terminal (opposites)

Charging

When a capacitor gains a charge causing a potential difference across its plates

Circuit

Conducting path from to positive terminal of a power source to the negative terminal of a power source

Circuit diagram

Diagram using symbols to represent an electrical circuit

Coil

Turns of electric wire around an object(e.g. Iron core)

Conductors

Materials that allow electric charges to flow through them easily

Conventional Current

Current flows from positive to negative terminal

Coulomb

Unit used to measure quantity of electric charge

Current

A flow of electricity through a conductor

Dielectric constant

Proportion by which the capacitance increases when an insulator is placed between the plates of a capacitor

Direct current

An electrical current that always moves in one direction

Discharging

When a capacitor loses a charge causing a potential difference across its plates

Electric Field

The field around charged particles that exerts a force on other charged particles.

Electric potential energy

Potential energy due to the position of an electrical charge near other charges

Electrical conductors

Materials that have electrons that are free to move throughout the material; for example, metals

Electrical energy

A form of energy from electromagnetic interactions; one of five forms of energy-Mechanical, chemical, radiant, electrical, and nuclear

Electrical force

A fundamental force that results from the interaction of electrical charge and is billions and billions of times stronger than the gravitational force

Electrical insulators

Electrical nonconductors, or materials that obstruct the flow of 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

One of four fundamental forces; the force of attraction or repulsion between two charged particles

Electromagnetic induction

Process in which current is induced by moving a loop of wire in a magnetic field or by changing the magnetic field

Electron current

Opposite to conventional current; that is, considers electric current to consist of a drift of negative charges that flows from the negative terminal to the positive terminal of a battery

EMF

Voltage across a power supply when no current is drawn

Faraday's Law

The induced voltage (EMF and current) in a coil is proportional to the product of the number of loops and the rate at which the magnetic field changes within those loops

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

Inductor

Produces opposing voltage when current-magnetic field changes

Internal resistance

Resistance inside a battery/power supply

Kirchhoff's current law

Total current entering a junction = total current leaving a junction

Kirchhoff's voltage law

The total of all the voltages in a closed loop is equal to zero

Lenz's law

The direction of the induced current creates a force that opposes the change that produces it

Magnetic Dipole

Magnet with two poles (North & South); all magnets are dipoles; cutting one in half creates two dipoles

Magnetic field

Region where ferromagnetic materials (iron, cobalt, nickel) and magnets experience a force

Magnetic Field Lines

Invisible lines that map out the magnetic field around a magnet

Magnetic flux density

Amount of flux density in a fixed area

Magnetic poles

The ends, or sides, of a magnet about which the force of magnetic attraction seems to be concentrated

Magnetism

The force of repulsion (pushing) or attraction (pulling) between poles of magnets

Mutual Inductance

Changing current in one coil induces a voltage in another coil

Ohm

Unit of resistance equivalent to volts/amps

Ohm's Law

The law that states that resistance is equal to voltage divided by current (R=V/I)

Permittivity

Proportion by which the capacitance increases when an insulator is placed between the plates of a capacitor

Phasor

Anti- clockwise rotating vector used to help draw sine graphs

Positive electric charge

One of the two types of electric charge; repels other positive charges and attracts negative charges

Potential Difference

Difference in voltage between two points

Power

The rate of doing work is called power. Power is a scalar quantity. The SI unit of power is Watt ( 1 W = 1 Js-1)

Power Dissipated by a Resistor

P = IV (applying Ohm's law) = I²R = V²/R [P=power (W/t), I=current (amp), V=voltage (volt), R=resistance]

Reactance

Ability of a capacitor or inductor to limit current in an A.C. circuit

Resistance

A material's opposition to the flow of electric current, measured in ohms

Resistors

Objects that allow charge to flow at a reduced rate (change into heat or light)

Secondary coil

Part of a transformer, a coil of wire in which the voltage of the original alternating current in the primary coil is stepped up or down by way of electromagnetic induction

Series

Electrical connection of components in such a manner that current flows first through one and then through the other

Solenoid

A cylindrical coil of wire that becomes electromagnetic when a current runs through it

Terminals

Ends of a battery that a circuit is connected t

Tesla

Unit of Magnetic field strength

Time constant

Time for voltage/current to change by 63% (Capacitor or Inductor)

Transformers

A device that transfers electric current from one circuit or set of circuits to another, by means of electromagnetic induction and usually for the purpose of changing voltage.

Uniform electric field

An electric field of constant strength where field lines are parallel and equally spaced

Voltage

Measure of energy per unit charge (W/Q)

Voltage drop

The electric potential difference across a resistor or other part of a circuit that consumes power

Voltmeter

Device that measures voltage and is connected in parallel to a component