Static Electricity
Electricity & Magnetism
Static Electricity
Matter is composed of small particles calledatoms.
The atom is composed of protons, neutrons,and electrons.
Normally, atoms are neutral (no charge)because they have the same number of protonsas electrons.
Some substances can gain and lose electronseasily because of their properties.
Static Electricity
When a balloon isrubbed with a woolcloth (friction), thewool cloth loses someof its electrons.
Because the wool clothnow has more protonsthan electrons, it ispositively charged.
The balloon has gainedelectrons and is,therefore, negativelycharged.
By bringing thenegatively chargedballoon into contactwith positivelycharged items, theybecome attracted.
Law of Electrostatics
This is an example of oneof the basic Laws ofElectrostatics: Unlikecharges attract eachother.
It also states that likecharges repel.
Example: If two negativelycharged balloons arebrought near each other,they repel each other.
Static Electricity
Electrons sometimes jump betweenobjects. When this happens we sometimeshear a “crack” and, in darkness, see aspark.
Producing ElectricEnergy
Electricity & Magnetism
Magnets and Magnetism
An electric current flows when electronsmove from atom to atom through aconductor.
In 1820, Hans Oerstead, a Danishphysicist, discovered that electric currentpassing through a wire produces amagnetic field around the wire.
If the wire is coiled around an iron ore anelectromagnet is produced.
Producing Electric Energy
Other methods of generating electric currenthave been found, such as with chemicalenergy.
The wet cell, a battery, consists of a copperstrip (positive electrode) and a zinc strip(negative electrode) in a diluted acid solution.
The acid solution, known as an electrolyte, iscapable of conducting an electrical current.
Producing Electric Energy
Electrons leave the copper strip,giving it a positive charge. As the zincdissolves, it has surplus electrons,giving it a negative charge.
Electrons flow from the zinc stripthrough the conductor to the copperstrip.
The electrical current produced fromthe flow of electrons can cause abulb to light.
Producing Electric Energy
The current produced is calleddirect current (D.C.).
Heat energy can also be usedto generate an electricalcurrent.
When set of dissimilar metalstrips (called thermopiles) areheated, an electric current isgenerated that flows throughthe connecting wires.
Producing Electric Energy
An instrument called theammeter measures electriccurrent.
Sunlight can also be used toproduce electricity.
Solar cells consist ofsemiconductors made of siliconcrystals.
The sun’s energy can causeelectrons to flow between thesemiconductors, producing asmall current.
Producing Electric Energy
A power plant generator consists ofelectromagnets that are made to spin withinan armature, which consists of many coils ofwire.
The process begins with a turbine, which willturn from the force of wind, moving water, orheated water (steam).
Producing Electric Energy
At the spinning of theturbine and shaft causeelectromagnets to spinwithin the armature.
This current is used tosupply theelectromagnets and tosupply electrical energyfor consumers.
The current generated iscalled alternatingcurrent (A.C.)
Complete Circuits
Electricity & Magnetism
Complete Circuits
The electrical energyproduced by a generatoror battery can be made tofollow certain paths.
The flow of electricalenergy is called anelectrical current.
The electrons flow in ametal conductor, such ascopper wire, is from thenegative to positive pole.
Complete Circuits
The path taken by the electrical current is knownas a circuit.
When the pathway is unbroken and the currentflows from the source through the conductor andback again, the circuit is said to be complete.
Complete Circuits
When someone flips on a lightswitch, the circuit is completeand electrical current flowsthrough the light bulb,producing light.
When someone pushes adoorbell button the circuit iscomplete and the bell rings.
The complete circuit is alsocalled a closed circuitbecause there is no openingor break in the path ofelectron flow.
Complete Circuits
A switch allows oneto control the flow ofelectrical current.
When the switch isopen, or in the offposition, the currentcannot flow throughthe conductors.
This is called an opencircuit.
Complete Circuits
If the electric current completes a circuit withoutservicing the device it was intended to operate, as whentwo bare conductor wires come in contact with eachother, a “short circuit” results.
This causes the wire to heat up without operating theelectrical device.
Series and ParallelCircuits
Electricity & Magnetism
Series and Parallel Circuits
Electrical current can bemeasured in several ways.
Electrons flow through aconductor when there is asurplus of electrons at onepole and a deficit at theother pole.
The electrical potential of thetwo poles is different. Thisdifference is known as theelectromotive force (EMF), orvoltage.
The instrument used to measure voltage is thevoltmeter.
The rate of flow of the electrical current ismeasured in units called amperes (amps).
The ammeter is the instrument used to measureamperage.
As the electrons move through the conductor, acertain amount of opposition is known asresistance and is measured in units calledohms.
Series and Parallel Circuits
Series and Parallel Circuits
Various factors affect the resistance of aconductor:
Type of material
Thickness of material
Length of material
Series and Parallel Circuits
A complete circuit can be set upin two ways, a series orparallel circuit.
In the series circuit theelectrons have only one paththrough which they may flow.
When two bulbs are connectedin series with one dry cell, theammeter shows that thestrength of the current is lesswhen compared to a one bulbcircuit because the second bulbacts as a resistor.
Series and Parallel Circuits
When two bulbs are connected in parallel withone dry cell, the ammeter indicates greateramperage compared to the one bulb circuit.
This is because the current has more than onepath to follow so there is less resistance.
Magnets andMagnetism
Electricity & Magnetism
Magnets and Magnetism
Magnetic iron ore wasdiscovered by the Greeksin a region once known asMagnesia.
Natural magnets, calledlodestones, are composedof the mineral magnetite.
Certain materials such asiron (steel), nickel, andcobalt are attracted tomagnets and can beformed into magnets ofvarious shapes.
Magnets and Magnetism
The domain theory of magnetism is based on theconcept of the magnetic field of individual atoms.
Certain elements, such as iron, can becomealigned.
The aligned clusters of atoms then form magneticdomains within pieces of iron.
Magnets and Magnetism
The attraction orrepulsion is strongestat the ends, calledpoles.
One end is the northseeking pole (N) andthe other is the southseeking pole (S).
When like poles arebrought together theyrepel each other,unlike poles attracteach other.
Magnets and Magnetism
The magnetic field in the space arounda magnet is defined by the lines offorce.
The patterns of these invisible lines offorce can be seen when iron filings aresprinkled around a magnet.
Magnets and Magnetism
The earth behaves as a huge magnetand therefore has magnetic lines of force.
It is these lines of force that align the northend of a directional compass needle tothe magnetic north pole of the earth.
Electromagnets
Electricity & Magnetism
Magnets and Magnetism
In an unmagnetized piece ofiron the domains are randomlyoriented.
However, if the piece of iron isplaced next to a strongmagnet, many of the domainswill arrange themselves in linewith the magnetic field.
Electromagnets
Electromagnets have three requirements:
Electric current
Coiled, insulated wire
A soft iron bar
When a current flows through the coiled wire wrappedaround the bar (core), the bar and coiled wire act like amagnet.
They can pick up objects and they have north and southseeking poles.
Electromagnets
For electromagnets, asoft iron bar is usedbecause it magnetizeseasily and also loses itsmagnetism easily.
An electromagnet willcontinue to be a magnetas long as the currentflows through the coiledwire.
For this reason,electromagnets arecalled temporarymagnets.
Electromagnets
When a current flows througha wire, a magnetic field (linesof force) occurs.
In an electromagnet the linesof force occur around the softiron core and coiled wire.
The electric force of anelectromagnet can be madestronger in two ways:
By increasing the number ofturns of coiled wire aroundthe core
And/or by increasing theamount of electric current
Electromagnets
Doubling the number of turns ofwire or doubling the electriccurrent will double themagnetic force of theelectromagnet.
The poles of the electromagnetcan be reversed by reversingthe wire connection at thesource of electricity.
Pole designation may bedetermined by using acompass.
Electromagnets
Electromagnets are used in many objects:
Telephones
Telegraphs
Radios
Televisions
Motors
Doorbells
Electrical appliances
