Physics 3.6 Electrical Systems

Alternating Current (A.C.)

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.

Current definition, units and symbol

Current is the flow of charge (I, A)

Capacitance definition, units and symbol

Measure of a capacitor's ability to store charge.

Capacitor

Device that stores electric charge on two oppositely charged plates.

Charging a Capacitor

A capacitor gains a charge causing a potential difference across its plates.

Coil

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

Conductors

Materials that allow electric charges to flow through them easily due to freemoving electrons

Conventional Current vs electron flow

Electrons flow negative to positive but the current is positive to negative

Charge definition, units and symbol

q (C)

Current Electricity

A flow of electricity through a conductor.

Direct current

An electrical current that always moves in one direction.

Dielectric constant

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

Discharging

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

Electric circuit

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

Electric Field

The field around charged particles that exerts an electrostatic force on other charged particles. (pos to neg)

Electric field lines

A map of an electric field representing the direction of the force that a positive charge would experience.

Electric Flux definition, units, and symbols

The product of a surface area and the component of the electric field perpendicular to the surface.

Electric Potential/Voltage

The difference in electrical charge between two points in a circuit expressed in volts (AKA potential difference). (V, V)

Electric potential energy

Potential energy due to the position of a charge near other charges. (E, J)

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.

Electrical force

A fundamental force that results from the interaction of electrical charge.

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.

Electromotive force (EMF)

The pressure, or force, that causes electric current to flow.

Electromagnetic induction

Current is induced by moving a loop of wire in a magnetic field or by changing the magnetic field.

Induced voltage

Voltage created by the combination of movement and a magnetic field.

Faraday's Law

Induced voltage in a coil is the sum of the number of loops and the rate at which the magnetic field changes.

Generator

Device that converts mechanical energy into electrical energy from the rotation of a coil inside a magnetic field

Impedance

Combination of resistance and reactance in an AC circuit.

Insulators

Materials that are poor conductors of electricity due to no freemoving charged particles

Inductance

The effect in a circuit when a changing current causes an opposing induced voltage.

Internal resistance

Resistance inside a battery/power supply.

Kirchhoff's current law

Total current entering a junction equals 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 made up of dipoles.

Magnetic field

A region of space in which ferromagnetic materials (iron, cobalt, nickel) and magnets experience a magnetic force (north to south)

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 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.

Mutual Inductance

Changing current in one coil induces a voltage in another coil.

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.

Power

The rate of doing work (P, W)

Reactance

Ability of a capacitor or inductor to limit curent in The opposition to current flow in an AC circuit due to capacitance and inductance.

Resistance

A material's opposition to the flow of electric current. (R, ohms)

Resistors

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

Secondary coil

Coil of wire in which the voltage in the components is stepped up or down.

Solenoid

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

Superconductors

Some materials in which, under certain conditions, the electrical resistance approaches zero.

Magnetic field strength

B, T

Time constant

Time for voltage/current to change by 63%.

Transformers

Device that transfers electricity from one circuit to another by means of electromagnetic induction.

Uniform electric field

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

Voltmeter

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

Voltage drop

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

Voltage-current characteristics

Graphical representation of voltage against current for a particular component.

Induction

Conversion of Ek to electrical energy using a magnetic field

Inductor

produces opposing voltage when current-magnetic field changes

back emf

an emf induced due to a change in magnetic flux. From Faraday’s law, the induced emf will be proportional to the change in flux. From lenz’s law, the induced emf will oppose the change that created it (the emf from the battery).

explaining current when a inductor is in parallel

at first, when the switch is closed the current through the circuit increases quickly. This change in current induces a back emf in the inductor which opposes the current, so the current through the inductor increases more slowly than the current through the bulb. As the current increases in the inductor, its rate of change decreases until it reaches a steady state. At this point there is no change in current so there is no back emf opposing the current and so most if not al of the current wil flow through the inductor’s branch