P6 Electric Current, Resistance, and Electromotive Force

some common alternative sources of electricity

Wind, sun, biofuels, water, and waves

electric current

the amount of charge flowing per unit time.

whenever there is a potential difference (voltage) between the terminals of a source.

when does charges flow

electricity

flow of charges in a conductor

charges

It usually progresses from a positive to a negative terminal.

current

flow of electric charge.

ampere

SI unit of electric current

current

In electric circuits this charge is often carried by moving electrons in a wire

voltage

the potential to flow, Increases the further distance up.

resistance

the pushing back against flow, decreases if pipe width is bigger.

current

the actual flow, increases when voltage is high and resistance is low.

thickness

length

material

temperature

Four components change the resistance of a wire

Resistance

Less ____ Allows More Current

Increases

______Resistance (Less Current)

thinner the wire

The ___________ the less electrons can flow

longer the wire

The ____________ the more distance from point A to point B

lower conduction

The material of the wire, the ____________, the harder it is for electrons to flow.

Higher temperatures

____________ increase resistance in a wire.

Decreases

_______ Resistance (More Current)

wider the wire

The ____________ the more electrons can flow

shorter the wire

The _____________ the less distance from point A to point B

higher conduction

The material of the wire, the ___________, the easier it is for electrons to flow

silver

copper

gold

aluminum

Top Conductive Metal Elements

Lower temperatures

___________decrease resistance

battery

fuse

load

resistor

open switch

closed switch

Common Symbols Used In A Circuit

battery

A long line next to a shorter line.

positive terminal (cathode)

long line represents what

negatuve terminal (anode)

short line represents what

battery

provides the source of electrons in a circuit.

fuse

This is a safety device added to a circuit.

fuse

This protects from fire or equipment damage that could result from an excessive current.

circuit breaker

safety device to protect from damage including fire with the same purpose as a fuse.

circuit breaker

When too much current is present the circuit will open. This will be manually reset to close the circuit again.

load

This is any device the circuit can power

load

It can be a light, speaker, toaster oven, or anything else.

resistor

This is a device specialized to slow down the current in a wire.

open switch

The symbol it two dots with a slanted open wire in the middle showing an open circuit.

closed switch

The symbol is two dots with a wire still connected in the middle showing a closed circuit.

closed

A circuit must be ______to have electrons flow (current) and the load on

off

A open circuit is ____

on

A closed circuit is _____

electric field

A potential difference (V) between two points creates an _______

circuit

An electric field moves through a ______setting electrons in motion

electron drift.

Electrons move slowly bouncing around in many directions as they gradually follow the direction of current. This random patter is called

heat

always a side effect of electric current

electron drift

why is Heat always a side effect of electric current

rectification

The process of turning AC into DC

rectification

can be done using diodes

diodes

electronic components that allow a flow to occur one way but not the other.

direct cuurent DC

an electric current that is uni-directional, so the flow of charge is always in the same direction.

alternating current AC

flow of electric charge that periodically reverses.

battery

always provides a direct current with conventional current flowing from the positive terminal to the negative.

common outlet

will have alternating current when you plug an appliance into the wall. Often there will be a rectifier to convert alternating current (AC) into direct current (DC) as many appliances require DC current.

Benjamin Franklin

, introduced the terms positive and negative charges

conventional current

electric current was defined as the flow of positive charges from the positive terminal to the negative terminal of a source of voltage.

benjamin franklin

introduced the words plus, minus, positive, negative, charge, and battery.

electron current

current in a metallic conductor is actually a flow of electrons from the negative terminal to the positive terminal.

conventional current

Electron current is equivalent to the ___________ flowing in the opposite direction

electric currrent (I)

the amount of charge passing through any point in a conductor per unit time.

ampere

was considerd “the Isaac Newton of electricity”

André Marie Ampére

He was the first to describe current as a continuous flow of electricity along wire

André Marie Ampére

The unit ampre is named after the French scientist and mathematician,

André Marie Ampére

He found ed the science of electrodynamics-the study of charges in motion

Electrical resistance, or simply resistance,

the opposition of material to the flow of electric current.

ohm (Ω)

The SI unit of resistance

Georg Simon Ohm

ohm was named after who

resistors

Most electrical connection use devices called ____ to regulate the amount of current passing through a conductor.

fixed

variable

Resistance values of the resistors may be ____ or _______.

variable resistances

Potentiometers, light dependent resistors, thermistors, and wire-round rheostats

fixed resistance values

Metallized film resistors, carbon resistors, wire-wound resistors, and chip resistors

metal film resistors

have a thin metal layer as resistive element on a non-conducting body.

metal film resistors

They are among the most common types of axial resistors.

carbon resistors

contain both solid carbon (graphite) and a clay additive to help with durability and were more common prior to the early 1970s.

wire-wound resistor

an electrical passive component that limits current. The resistive element is an insulated metallic wire that is wound around a core of nonconductive material

chip resistor

a passive electronic component that limits the flow of Direct Current (DC) and Alternating Current (AC)

chip resistor

Among its properties is to lower the voltage or maintain the current constant inside an electronic circuit

INTERNATIONAL ELECTROTECHNICAL COMMISSION (IEC)

AMERICAN NATIONAL STANDARDS INSTITUTE (ANSI)

Two sets of symbols are used to represent resistors

6 or 7

how many bands colors does resistor have

electrodes and electrolytes

A battery consists of cells. Each cell basically consists of two _________

internal resistance of a cell

Cells also offer low resistance to electric current

r

Internal resistance is usually represented by

internal resistance

because of this, the potential difference across the terminals of cell when current is flowing through it is less than when there is no current.

electromotive force

potential difference across its terminals when no current is flowing called

electromotive force

the voltage indicated on a battery.

terminal voltage (TV)

The potential difference across the terminals of a cell when current (I) flows through

alessandro volta

invented the first electron cell in 1799

voltaic pile

It consisted of alternating disks made of zinc and silver with a piece of cloth soaked in salt solution between them.

voltaic pile

formed of the basis of modern cells and batteries such as the dry cells, storage battery, and nickel-cadmium cell.