Physics Unit 7 (Electricity)

Charging by conduction

A charged object (CO) is placed in contact with the other object (OO) Some electrons on the CO can move to the OO When the CO is removed, the OO is left with a charge The object being charged is always left with a charge having the same sign as the object doing the charging No matter what the shape of the conductor, excess charge always resides on its outer surface.

rectifiers

Diodes which convert AC to DC for typical use

Columb's Law v. Newton's Law of Gravitation

F = k(q1 * q2) / r^2 F = G (m1 * m2) / d^2 k = 9.0 x 10^9 N m2 / C2 k = 6.67408 × 10^-11 m3 kg-1 s-2 (electric constant bigger shows that it is a more powerful force) charge in Columb's mass in Newton's electric force is repulsive or attractive gravitational force is one way

polarization

In most neutral atoms or molecules, the center of positive charge coincides with the center of negative charge In the presence of a charged object, these centers may separate slightly This results in more positive charge on one side of the molecule than on the other side This realignment of charge on the surface of an insulator is known as...

When a positive charge is placed in an electric field

It moves in the direction of the field It moves from a point of higher potential to a point of lower potential Its electrical potential energy decreases Its kinetic energy increases

When a negative charge is placed in an electric field

It moves opposite to the direction of the field It moves from a point of lower potential to a point of higher potential Its electrical potential energy increases Its kinetic energy increases Work has to be done on the charge for it to move from point A to point B

conventional current direction

The direction of the current is the direction positive charge would flow

Direction of electric fields

The electric field produced by a negative charge is directed toward the charge The electric field produced by a positive charge is directed away from the charge

charging by induction

The presence of a charged object near a neutral conductor forces e- within the conductor to move, leaves an imbalance of charge on opposite sides of the neutral conductor. A ground is brought near and touched to one of the sides, permits a flow of electrons between the object and the ground. The flow of electrons results in a permanent charge being left upon the object. When an object is charged by induction, the charge received by the object is opposite the charge of the object which was used to charge it.

The superposition principle

The resultant force on any one charge equals the vector sum of the forces exerted by the other individual charges that are present

Law of Conservation of Change

The total charge (the difference between the amount of positive and negative charge) within an isolated system is always constant. Charge is not created, only exchanged Objects become charged because negative charge is transferred from one object to another

resistance factors

Type of Material Physical Dimensions (of the material) Temperature (higher = more resistance)

triboelectric series

a list of materials, showing which have a greater tendency to become positive or negative used to determine which combinations of materials create the most static electricity

resistance

a measure of how easily (or NOT) current flows through a material arises due to collisions between the electrons carrying the current with the fixed atoms inside the conductor ALL materials have SOME resistance, even wires and batteries, but this is so small we can ignore it.

charge carrier

a moving charge

transitors

a semiconductor device with three connections, capable of amplification in addition to rectification -Collector -Base: controls current flow based on current supplied -Emitter switches: when current is fed into the BASE layer the transistor will ALLOW current flow logic circuits: conditions must be electronically met for current to flow and allow a subsequent condition to be fulfilled

Diodes

act as one-way valves to control the direction of current flow. Positive charge carriers (holes) move in the direction of the arrow forward-biased = allow current flow reverse-biased = prevent current flow

variable resistors (potentiometers)

allows for smooth changes in the level of resistance in a circuit. Volume control on audio equipment is one application

measuring current

ammeter

Coulomb's Law

an electrical force has the following properties: It is along the line joining the two particles and inversely proportional to the square of the separation distance, r, between them It is proportional to the product of the magnitudes of the charges, |q1|and |q2|on the two particles It is attractive if the charges are of opposite signs and repulsive if the charges have the same signs -------------------------------------- The electrical force is a vector quantity; therefore, the net force on any one charge is the vector sum of all the forces exerted on it due to each of the other charges interacting with it independently.

semiconductors

characteristics are between those of insulators and conductors electrons (in varying numbers) can carry current depending upon the voltage supplied and the *impurities* in the material Silicon and germanium

P-N Junctions

created when the N- and P-Type layers are placed together the excess electrons are paired with the "holes" until an equilibrium is reached area of equilibrium is called the *Depletion Zone*, and it resists flow below a minimum voltage

capacitor

device used in a variety of electric circuits

A positive charge ____________________ when it is moved in a direction opposite the electric field

gains electrical potential energy

fixed resistors

have well-defined an unchanging resistance values indicated by the color-codings on the outside

A negative charge __________________ when it moves in the direction opposite the electric field

loses electrical potential energy

insulators

materials in which electric charges do not move freely electrons are tightly bound to the atomic nuclei and cannot move about or carry current rubber and glass

conductors

materials in which the electric charges move freely in response to an electric force many atoms' electrons are free to move about and carry current Cu, Au, Ag

multimeter

measures voltage/current, depending upon its setting

electric fields run...

positive to negative

current

rate at which the charge flows through a surface charges flow perpendicularly to a surface of area A

electric field

said to exist in the region of space around a charged object

potential difference

the change in the potential energy (final value minus initial value) of a charge q moved from A to B divided by the size of the charge

When another charged object enters this electric field,

the field exerts a force on the second charged object

bias voltage

the minimum required voltage to get current going

electric potential

the potential energy per unit charge defined according the to convention of the Electric Field direction, in that... HIGHER Electric Potential is at the POSITIVE end of the field. LOWER Electric Potential is at the NEGATIVE end of the field

capacitance

the ratio of the magnitude of the charge (Q) on either conductor (plate) to the magnitude of the potential difference (V) between the conductors (plates)

measuring voltage

voltmeter

Coulomb (C)

The SI unit of charge e = 1.6 x 10^-19 C

electric forces

Like charges repel Opposing charges attract

impurities in semiconductors

N-Type (cathode): provide an EXCESS of electrons to the material; negative charges carry current P-Type (anode): CONSUME electrons, creating "holes," or positive charges, which carry current

electron

Nature's basic carrier of negative charge Gaining or losing these is how an object becomes charged have a charge of -e

proton

Nature's basic carrier of positive charge do not move from one material to another because they are held firmly in the nucleus have a charge of +e