Unit 10Electricity and Magnetism

Reference: Ch 20-26

What is Electricity? The flow of

electric current in wires, motors, light bulbs, and other devices.

Electric current carries energy over great distances.

Circuit Diagrams

Circuits: made up of wires and parts such as batteries, light bulbs, motors, or switches.

When diagramming circuits, use symbols to represent parts of the circuit.

Common Electrical Symbols

Straight lines represent

wires.

Battery

Resistor Light Bulb

Switch

NOTE: In many circuit diagrams, any electrical device is shown as a resistor. A resistor is an electrical component that uses energy. Sometimes when showing how a circuit works, light bulbs might be treated like resistors.

Open vs Closed CircuitsElectricity cannot travel through

an open circuit: path is broken.Electricity can travel easily

through a closed circuit: there is a complete path.

A short circuit is usually an accidental extra path for current to flow.

Electric Charge Is the source of shocks and

sparks Electrically charged: If

materials or objects carry excess + or – charge

Most matter is neutral (no charge)

An electroscope can detect charged objects.

The leaves attract or repel each other depending on the charge nearby

Like charges repel

Opposite charges attract

Electroscope

Batteries and Voltage

Batteries Use chemical energy to

move charges Amount of potential

energy = voltage Battery like a water

tower: water flows from high energy (top of tower) to low energy

Circuit transfers energy from battery to object

Voltage Electric charge flows from

high energy (voltage) to lower energy.

Voltage is measured using a voltmeter

All points on a wire are the same voltage.

Voltage is reduced when energy is used.

Supplies energy to make charges flow.

CurrentFlow of electric chargesDoes workMeasure current using an ammeterCircuit breakers or fuses stop too

much current from flowing.Types of current:

– Alternating (AC): direction of current goes back and forth

– Example: household current is AC– Direct (DC): current flows in one

direction.– Example: battery

Electrical Conductivity• Property of a substance: its ability for

current to pass through• Conductors- electrons come free and

can move to create electrical current• allow current to pass• metals

• Insulators- electrons are tightly bound to atoms and cannot move• block current• Usually nonmetals, some plastics,

foam or rubber• Semiconductors- in between in ability

to conduct current• Computer chips, LED’s, some lasers

Resistance Measures how easily charges flow through Compare to pouring water out of jar: if

opening is small lots of resistance; if opening is large water flows quickly b/c of less resistance

Ex: The more light bulbs strung together the higher the resistance. (decreasing the current)

Factors affecting resistance– Thickness

Thick wire has a lower resistance and can safely carry more current than thin wire

– Length The longer the wire, the more resistance

it has

Ohm’s Law The relationship between amps, volts and ohms Current

– Unit: Amps– Symbol: I

Voltage– Unit: Volts– Symbol: V

Resistance– Unit: Ohms– Symbol: R

Series vs Parallel CircuitsParallel Circuits

Current can take more than one path

If multiple bulbs are in circuit, if one goes out, the others will still light

Homes are wired with parallel circuits

Series Circuits Current can only take

one path If multiple bulbs in

circuit, if one goes out they all go out

Series circuits would not work in the home because all electrical items would have to be on all the time to keep the circuit closed