-
1
MakingaFaradayFlashlight
ExecutiveSummary:Thisprojectdemonstratestheprinciplethatamagnetpassingthroughacoilofwireinducesacurrent,whichinthiscaselightsanLED.TwoLEDsareused,onethatlightswhenthemagnetmovesinonedirectionandtheotherlightswhenthemagnetgoesbacktheotherway.Inarealflashlight,anadditionalcircuitwouldbeusedtocausethelighttostayon;thisisjustademoandisintendedtokeepcostsdown.Materialsneeded(perflashlight)Part
Number Partnumber Unitprice(June2011)
DescriptionWire 150ft Wire-MW-24-1/4 $8.60* Magnetwire,24gauge
http://www.bulkwire.com/wirecable/magnetwire.htmlMagnet 1 ND035
$1.29** Neodymiun(rareearth_magnet,disk,in.diameter,thick
http://www.magnet4less.com/product_info.php?products_id=123LED 2
1601665ND $0.36 LED3MM632NMALINGAPREDCLEAR
http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&KeyWords=1
601665ND&x=0&y=0Tube 4in 49035K23 $7.77for4ftlength)
ClearPVCpipe,
http://www.mcmaster.com/#clearpvcpipe/=cre6rrRubberbands 2
Tape,scissors,paper,andamatchorlighter*Formultipleprojects,thiswirecanbeboughtinlargerspoolsformuchless,e.g.http://www.magnet4less.com/product_info.php?products_id=195isapproximately8,700feetfor$107.Thiswireisabout790lb/foot.**About$1eachinquantity
-
2
Principleofoperation
FaradaysLawTheflashlightworksontheprincipleofFaradayslaw,whichsaysthatachangingmagneticfieldinducesanelectromotiveforce,producingacurrentinawire.Inourcase,themagnetismoving(whenyoushaketheflashlight),whichcausesachangingmagneticfield.Acoilofwireiswrappedaroundtheoutside,andthemovingmagnetinducesafield.
Figure 1. Faradays law.
http://sirius.ucsc.edu/demoweb/cgi-bin/?e_m-electmag-faraday
Aneatsimulationcanbefoundathttp://phet.colorado.edu/en/simulation/faradayslaw.LEDInourcase,wewillusethecurrenttolightupalightemittingdiode(LED).ThecircuitsymbolforadiodeisshowninFigure2.
Adiodeisadeviceinwhichcurrentflowsinonlyonedirection(thedirectionthearrowispointing).Thebaracrossthearrowtipremindsusthatcurrentcannotflowinthatdirection.
Figure 2. Current can flow only one direction in a diode.
Whenweshaketheflashlight,themagnetmovesbackandforth,resultinginacurrentthatreversesdirectionbackandforth.Therefore,wewillconnecttwodiodesacrossthewirecoil,inantiparallelconfiguration,Figure3.
-
3
Figure 3. The LEDs are connected anti-parallel.
TheLEDlampslookphysicallyasshowninFigure4.Oneleadisdesignatedtheanode,andtheotheristhecathode.TherearetwowaystotellthemapartontheLEDpackage.Thefirstistonoticewhichleadislonger.Thelongerleadistheanode.Ifsomeonehascuttheleadsoryoucantseethem,thebackupplanistolookfortheflatsideoftheflangeonthelampbody.Theflatindicatesthecathode.
Figure 4. The anode and cathode of an LED lamp, and how to tell
them apart.
http://www.societyofrobots.com/electronics_led_tutorial.shtml
Construction
1.
Windthecoil.Leavingabout6ofwirefreeatthebeginning,tapethewiretothesideofthetube.Wrapthewirearoundthetubeuntilabout6areleft,andtapethewiretothetube.
Thetapeisjusttokeepthewirefromunwinding.
Overlapthewireasmuchaspossible Neatnessdoesntcount.
Itisnotnecessaryorevendesirabletocovertheentirelengthofthetube.Youwantashort,densecoiltomaximizetheinteractionofthemagnetandthecoil.Youalsowanttheendsofthetubetoremainuncoveredsoyoucanseethemagnetinthere.
-
4
2.
BurnofftheinsulationThemagnetwirehasacoatingofinsulatingmaterialpaintedontoit,tokeepitfromshortingtoitselfwhenwoundintocoils.Tomakeelectricalconnections,youllneedtoburnitoff.Holdingtheendofthewireawayfromflammableobjects,usethelightertoburnoffabout1oftheinsulation.Youmayseethecoatingflareupinstantaneously.Itonlytakesasecondortwo.Whenthewirelooksblack,youhavesucceeded.Repeatfortheotherend.
Childrensometimeshavetroubleoperatinglighterswithsafetymechanisms.
Theinsulationcanbealsoremovedwithsandpaper,butitishardertogetalltheinsulationoff,andisnowherenearasmuchfun.
3.
ConnecttheLEDSToconnecttheLEDs,twisttogethertheanodeofoneLEDandthecathodeoftheother.Repeatfortheotherleads,Figure5.Makesurethetwopairsofleadsdonttoucheachother.TwistoneburnedoffendofthecoilwiretoeachpairofLEDleads.
4.
InsertmagnetandcaptubeInsertthemagnetintothetube.Cuttwocirclesofpaper,andrubberbandthemtotheendsofthetube.CAUTION:
Make sure you cover the ends of the tube with your thumb and finger
to prevent the very heavy magnet from becoming a projectile.
5.
ShakeandobserveCommentsIfyoudecidetoscalethisupordown,itisimportantthatthetubeinnerdiameterbeonlyslightlylargerthanthenmagnet.Ifthemagnetcanrotate,theeffectwillbelargelylost.Alsothetubeshouldbeslipperyenoughthatthemagnetcanslidefreely(e.g.,notrubber).
Figure 5. Connection of the LEDs.
