Building a "Wimshurst"Static Machine Craft Print

Project No. 279

Part 2. How to make accessories for the staticmachine to demonstrate static-electric phenomena

AFTER completing the Wimshurst staticmachine as described in part 1 (S&MApril '58) several accessories will be

needed to conduct experiments and demonstratethe phenomena of static electricity.

Static electricity, incidentally, was discoveredway back around 600 B. C, when the Greek phi-

Filling Jar with smoke todemonstrate how electriccharges precipitate anddissipate smoke. Whenstatic machine is operatedand electrodes in glass jarcharged, the rod electrodewill repel smoke particlestoward oppositely chargedilat electrode causing

smoke to disappear.

losopher, Thales, noticedthat if he rubbed a pieceof amber with wool, theamber attracted bits ofstraw and other lightmaterial. It is doubtfulif he knew that rubbingthe amber produced astatic-electric charge onthe surface of this mate-rial, causing an attrac-tion for other material(normally having an op-posite charge), and thathe in all probability wasthe discoverer of staticelectricity.

Benjamin Franklin didconsiderable experiment-ing with electricity inthe static field, and foundthat if two pieces ofmaterial were rubbed to-gether, one piece ac-

This interesting pattern oi discharges gives a pic-turesque demonstration of how electricity alwaystakes the path of least resistance, or through the foil(see Fig. 16), jumping the spaces rather than jump-ing across the ball gap where it would have to

overcome air resistance.

SCIENCE AND MECHANICS

quired a positive and theother a negative charge.He also discovered thatatmospheric electricity(lightning) and staticelectricity were the same."Static" refers to elec-tricity at rest, comparedto "current" electricity(ordinary power type)which flows throughsome form of suitableconductor. When twopieces of material arerubbed together, elec-trons (negative charges)are rubbed off one anddeposited on the other.The material losing elec-trons becomes deficient

that electricity followsthe path of least resist-ance, can be accom-plished by making theaccessory shown in Fig.16. Make sure that plusand minus brass stripsare in good contact withthe aluminum-foil piecesat the ends. Photographsof this experiment, takenin a darkened room areshown in Fig. 1B of Part1 and Fig. 15.

Electric "Whirl." Op-eration of the whirl Fig.17 (made as in Fig. 18),is based on the fact thatthe density of the chargeat the pointed ends ofthe pivoted arms is sogreat that the air mole-cules in the immediatevicinity become charged.These charged air par-

ticles are known as "ions." Those becoming oflike charge repel one another as well as causingrepulsion between them and the arm tips. Thisforce of mutual repulsion causes the arms to ro-tate at high speed (Fig. 17). It should be remem-

Electrostatic energy activating a pair of pivotedarms, produces an interesting twin whirl. Plastic isused for base and shafts support to insulate metal

from ground.

in electrons, thereby leaving a surplus of protons(positive charges), and the piece becomes posi-tively charged. The piece acquiring the additionalor an excess of electrons in its atomic structure,becomes negatively charged.

This Wimshurst static machine is designed toprovide a constant source of static electricity ata potential up to about 60,000 volts. This highvoltage, however, is quite harmless since the cur-rent involved is very small. Nevertheless, quitea shock can be felt if the two spark-gap balls orrods are touched when the condensers (Leydenjars) are charged. It is, therefore, advisable todischarge the condensers after each experimentby pushing the balls togther by means of theinsulated handles. High humidity conditionsprevent building up static charges. This can beminimized by wiping the plastic terminal stripof the machine with a dry cloth, and wiping bothdisc surfaces by lightly applying a dry clothwhile operating the machine.

Illuminated Letters and Lightning Effect. Aninteresting and picturesque experiment, proving

Steel ball in a plastic tube demonstrates repulsionand attraction. The ball on touching a charged ter-minal acquires a like charge and is repelled towardthe oppositely charged terminal which attracts it.The ball then receives a like charge and is againrepelled, repeating its cycle of repulsion and attrac-

tion as long as terminals remain charged.

JUNE, 1958 145

A swinging pendu-lum with a metalball attached is an-other version ofdemonstrating re-pulsion and attrac-tion, operating onthe same electricprinciple as ball in

tube (Fig. 19).

bered in this andsubsequent ex-periments that likecharges always re-pel; unlike chargesattract. To operatethe whirl, attachlead wires with"alligator" clips atboth ends to pivotsand spark-gap rodsof machine. Aftera few seconds ofoperating machine,condensers will becharged and armsrotate. It is important that arms balance onpointed pivots, and that spark-gap balls are farapart to prevent a spark discharge. To make thepivot depressions, use a center punch lightly soas not to puncture the metal.

Activated Ball. Repulsion and attraction canbe demonstrated in an experiment with a steelball in a plastic tube (Fig. 19). Make the ac-cessory as detailed in Fig. 20. To operate, removethe spark-gap-ball assembly and clamp brassstrips of accessory in spark-gap terminal posts.Start machine and, if necessary, tip slightly sothat ball rolls in contact with a strip. Tube shouldbe clamped level. With the machine operatingand the ball contacting one metal strip, the ballreceives a like charge as the strip is repulsedtoward the opposite strip having opposite polar-ity and thereby attracting the ball. On contact,the ball receives the strip's charge and is againrepelled, traveling back and forth as it receiveslike charges from opposite strips.

Electrostatic Pendulum. Another experimentin attraction and repulsion can be achieved witha free-swinging pendulum built as shown in Fig.22 and mounted on the machine as in Fig.

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21. Here again, the ball receives the same chargeas the spark-gap ball it touches and is imme-diately repelled; performing in the same manneras ball in tube. Proof that condensers, or capac-itors as they are often called, store electricalenergy can be demonstrated by stopping themachine. The pendulum will continue to swinguntil the condensers have exhausted their storedenergy. To operate, start machine and gentlymove pendulum ball in contact with a spark-gapball. The pendulum arm must swing quite freelywith a minimum of friction.

Smoke Elimination and Precipitation. Com-mercial smoke precipitation can be duplicatedin miniature with a glass jar containing suitableelectrodes as in Fig. 23. Drilling or grinding thehole in the glass jar for the rod electrode is notdifficult when done on the drill press. Cut off ashort piece of brass tube squarely and saw anotch across the tube end about 1/4-in. deep (Fig.28). Set your drill-press speed to about 1275 rpm.Apply coarse carborundum valve-grinding com-pound liberally and drill, feeding compoundaround drill and using light pressure. No sharp-ening of drill is necessary, the important thingbeing to keep compound in contact with drillface, it being the compound and not the brasstube that does the actual drilling or grinding. Toform the copper screening, first wrap around a3/32 in. dia. rod, squeeze tightly around rod andallow sharp ends to project outward as in Fig.23. Press over rod electrode from open end ofjar. The rubber grommet in hole will keep rod

When static machine is operated charging hollow-cylinder, electroscope outside of cylinder (above)separate. Electroscope inside cylinder remains atrest, proving that charge exists only on outer surface

of hollow cylinder.

in place if it is a tight fit. Flat electrode is heldin place by aluminum jar clamp.

The positive-rod electrode, containing copperscreening with open ends or points, causes theminute particles of matter (mostly carbon com-posing smoke) suspended between the electrodesto become positively charged. And, being repel-led toward the flat or negative electrode, aredeposited thereon, thus eliminating the smoke.Some commercial smoke-elimination processescollect these carbon deposits as a carbon-blackby-product. To operate, connect clip leads as inFig. 14. Widely separate spark-gap balls, andblow smoke into glass jar. Start machine and in

Left, to more dramatically demonstraterepulsion, a plume consisting of stripsof paper is attached to top of cylinder.Plume is at rest indicating no charge

on cylinder.

Below, left, when the cylinder ischarged, the individual strips are vio-lently repelled because each strip has

received a like charge.

Below, if a grounded object, such asyour finger tips comes near the stripsof paper, they will be attracted to thefinger tips, demonstrating that opposite

charges attract.

a few seconds thesmoke will havedisappeared, leav-ing a deposit onthe flat electrode.

E lectroscope.One experimentwhich proves thatan electric chargeon any hollow con-ductor, such as acylinder or ball,will invariablytravel to the outersurface, can beachieved by mak-ing the accessoryshown in Fig. 25.To operate, attachthe two electro-scope units of .001-in. or thinner sheetbrass with Scotchtape to the bracketsuppor t s andslightly bend apart.Adjust spark-gapballs on machine

JUNE, 1958 147

widely apart and attach a clip lead to right-hand spark-gap rod and aluminum cylinder(Fig. 24). Start the machine and you will findthat the brass strips attached to the outsidesurface of the cylinder will separate (repulsion),while those on the inside will not, proving thatthe outside strips only are receiving a charge ofelectricity.

Electric "Plume." An interesting demonstrationof static charges involving repulsion and attrac-tion can be achieved by removing the brass stripsfrom the electroscope and attaching a bundle ofthin soft paper strips to the brass rod (Fig. 25A).The paper strips are best cut from facial tissue,about 3/16-in. wide, and so arranged around therh, screw to form a plume (Fig. 26). When themachine is operated, the paper strips will riseand widely separate (Fig. 27). If the machine isstopped, the strips will fall slowly as the chargein the condensers gradually dissipates (Fig. 26).

Another experiment with the same equipmentis to hold your fingers, partly closed, over theplume with machine in motion. The strips willreach up and attach themselves to your fingertips (Fig. 28). In the first instance, the likecharges on the paper strips caused repulsion,spreading each strips away from its neighbor. Inthe latter experiment, your fingers, being of nega-tive potential through ground, and the stripsbeing positively charged, attraction by unlikecharges resulted.

Blowing a Candle Flame. You can observe anelectric "wind" effect from pointed conductorsnear a lighted candle (Fig. 29). Remove thespark-gap-ball assembly and attach a piece ofstranded wire to the right-hand spark-gap ter-

Demonstration of an interesting electric "wind" illu-sion. The density of the charge at the ends of thefrayed wire results in charging the molecules of airon one side of the candle flame with the same chargeas the wire, repelling the molecules. In addition, thecarbon particles in the flame receive a like chargeand are repelled also, which probably accounts for

most of the blowing illusion.

Normally, a fat spark would jump the ball gap whenmachine is in operation. But because of the pointedpin attached to one ball, the charges developed fol-low the path of least resistance (the pin) and are dis-sipated. No spark occurs because voltage is nothigh enough. This experiment demonstrates the ac-tion of a lightning rod attracting a lightning bolt

and carrying it safely to ground.

minal. Fan out the wire strands and place alighted candle near the wire ends. Start machineand candle flame will move away from the wireas if blown by a breeze (Fig. 32). Actually, how-ever, carbon particles in the flame becoming posi-tively charged, are being repelled by the positivecharges at the ends of the wire.

Lightning Rod. Lightning rods, with theirpointed ends, on buildings serve to draw electriccharges (lightning bolts) from the atmosphereto the ground harmlessly. You can demonstratethis on the machine with a pin soldered to apiece of spring brass clipped to one of the spark-gap balls (Fig. 30). Place the balls about % in.apart and start machine. The usual spark willnot jump the gap. The discharges are picked upby the pointed end of the pin and, assuming thispole of the machine is ground, the dischargeswould be sent to ground. Actually, a real light-ning bolt of many millions of volts would bevisible as a flash from source to lightning rod,the latter affording the shortest path to ground.Let it be said, however, that an elaborate andscientifically designed system of lightning rods isnecessary to adequately protect buildings fromNature's most ppwerful artillery.

Building this Wimshurst static machine is anexcellent project for a science class or individualexperimenter and the cost will be much less thana manufactured one.

Space does not permit the inclusion of manyother fascinating electrical experiments possiblewith the Wimshurst static machine, and access-ories which the science teacher and student canundoubtedly make.—HAROLD P. STRAND.

• Craft Prints in enlarged size for electrical equipmentare available at $1.50 each. Order by print number. Toavoid possible loss of coin or currency in the mails, wesuggest you remit by check or money order. (No C.O.D.'sor stamps). Now available, our new illustrated catalog of"186 Do It Yourself Plans," IOC. SCIENCE AND MECHANICS,450 East Ohio Street, Chicago 11, Illinois. Please allowthree to four weeks for delivery.

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