e-mag

E-Mag

It’s Electrifying!

ElectrostaticsStored

electricity, or electricity at rest

Static ElectricityA build up of electric charges in

an object or in an area of an object. Rubbing your feet on the carpet

so that you can “shock” someone

Phet simulation: http://phet.colorado.edu/simulations/sims.php?sim=Balloons_and_Static_Electricity 4.5 min, video: http://www.cbsnews.com/stories/2004/08/27/earlyshow/living/ConsumerWatch/main638947.shtml

How Do Refueling Fires Happen? Static charge picked up when re-

entering vehicle

Touching nozzle without discharging static electricity

A spark ignites fumes

More Safety GuidelinesDO NOT get back into your car when

refuelingDO NOT top off your tankIf a flash fire occurs, back away,

contact attendant, and most important:

LEAVE NOZZLE IN VEHICLE!

Electrical Forces

unlike charges attract

like charges repel

A: more than before rubbing?B: the same as before?C: less than before?

Rub a balloon on your hair, the balloon attracts you hair. Is the amount of charge in the balloon and your hair

Conductorsallow charges to flow through them easily electrons are not tightly anchored to the nucleus

Electrical Conductor

Not this kind of conductor!

Allow charges to easily flow through them

Insulators

Charges cannot easily flow through them.

Ex: plastic, styrofoam

Metal, wire

Plastic or rubber

Charging by FrictionTransfer of

electrons by friction between two objects rubbing a balloon so that it

will “stick” to a wall Travolta simulation: http://phet.colorado.edu/simulations/sims.php?sim=John_Travoltage

Charging by Direct Contact

Conduction… transfer of electrons when one object touches another. touching someone and “shocking” them

Charging by InductionTransfer of

electrons when objects are brought near each other, but do NOT touch.

How does Lightning start and end?

Induction: Balloon on wallWall is neutral and an insulator

+ move slightly towards balloon

- move slightly away from balloon

Wall is neutral but has small surface charge, sufficient to hold balloon

Van De Graaff Generator

Robert Jemison Van de Graaff invented the Van de Graaff generator in 1931.

The device has the ability to produce extremely high voltages -- as high as 20 million volts.

Electric Potential or Potential Difference

Commonly called Voltage DifferenceElectric Potential is

measured in volts (V)

Electric Current (I)

The flow of electric charges.Measured in amperes (A)There must be a potential

difference in order for current to flow

Bird on a Power LineSAFE: both feet are on the same voltage line thus no potential difference!

NOT SAFE: If one leg is on the ground or another wire and the other one is on the power line, then there is a potential difference between the bird’s two legs.

Potential Difference and the flow of current:

Voltage SourcesGenerators and

batteries provide sources of voltage. Dry cells (Duracell)

have a paste electrolyte.

Wet cells (car batteries) have a liquid electrolyte.

Generators

Convert mechanical energy into electrical energyex: household generators or

car alternators

Batteries

Energy is released during a chemical reaction. Dry cells (Duracell) have a paste

electrolyte. Wet cells (car batteries) have a

liquid electrolyte.

Resistance

Opposition to the flow of electric charges. It is increased if length is increased or width of wire is decreased.Measured in ohms ()

Electrical Resistance

Relationship between voltage (V), current (I) and resistance (R)V = IR

Ohm’s Law sim: http://phet.colorado.edu/simulations/sims.php?sim=Ohms_Law

Electric Current

The flow of electrons

Fact or Fiction?When you turn on a light switch, electrons

move rapidly from the socket to the lamp to light the bulb.

Direct Current (DC)Charges always flow in one

direction. Ex: batteryelectrons always flow from

the neg. terminal to the pos. terminal AC/DC simulations

http://phet.colorado.edu/simulations/sims.php?sim=Circuit_Construction_Kit_ACDC

Alternating Current (AC)

Current flows in one direction, and then in the other direction…back and forth. Most US circuits operate at a

frequency of 60 Hz.

AC/DC

Electrical Relationships

Water in a Hose

DC in a Wire

Electrical Units

Pressure Voltage (V) Volts (V)

Rate of Flow

Current (I) Amperes, Amps (A)

Friction Resistance (R)

Ohms (Ω)

Electric Power

Rate at which electric energy is converted into another form such as mechanical, heat or light energy.

Electric power (PE) is equal to current (I) times voltage (V) measured in watts (W)

PE = I V

Calculating Power

Energy Converted

Electricity used (energy converted) is equal to power (kW) times time (hours)Eelectric = Pt

What causes electric shock in the human body- current or voltage?

Current passing through the body depends on the voltage applied and the electrical resistance of the body. (ranges from 100 Ω if soaked in salt water to about 500,000 Ω if the skin is very dry)

Effects of Current on the body0.001 A – barely felt0.005 A – painful0.010 A – muscle spasm0.015 A – loss of muscle control0.1 A (100 mA) can be fatal if current

goes through the heart

Electric CircuitA closed path through which electrons

can flow. Ex: when you turn a light switch

ON, you create a CLOSED circuit, when you turn it off you are opening

the circuit Phet circuit http://phet.colorado.edu/simulations/sims.php?sim=circuit_construction_kit_dc_only

Types of CircuitsSeries: current has only one

path to take

Parallel: current can follow different paths throughout the circuit.

Series Circuits

Parallel Circuit

The basics of solving circuit problems…

Parallel Circuits

I adds up

V is constant

1 = 1 + 1 + 1 + ...Req R1 R 2 R 3

SERIES CIRCUITI is constantV adds upR adds up

Circuit Breakers

Guards against overheating. It has a piece of wire that bends at high temps, causing a switch to “flip” which “opens” the circuit

Transformers

Not these:

These:

TransformersUsed to step up (increase) or

step down (decrease) voltage through electromagnetic induction

Electromagnetic Induction

The process of inducing voltage by changing the magnetic field around a conductor

Power TransmissionPower can be transmitted very

long distances at high voltages and low currents, it begins at 120,000 V at power plants and is stepped down until it reaches the 120 V used in your home

Power to Your Home

110 V vs. 220 V plug

Electric MeterEach month the number of

kilowatt hours (kWh) is read and you are billed according to your usage

Magnetic PolesProduce magnetic

forces.

Every magnet has a North and South pole.

Opposite poles attract each other. Like poles repel.

Magnetic Fieldsspace around a

magnet where a magnetic force is exerted acts like an electric

field

Magnetic Declination

Magnetic DomainsThe domain is

determined by the alignment of the atoms in a magnet

A strong magnet has perfectly aligned atoms

The Earth’s Magnetic FieldA compass points

to the earth’s magnetic field, however the geographic and magnetic fields are not perfectly aligned