The Wimshurst machine was an electrostatic generator invented in 1883 by James Wimshurst. It consists of two counter-rotating disks with conductive sectors that induce opposite charges, which are collected by comb-like charge collectors and stored in Leyden jars. The high voltages produced allowed the machine to be used for early X-ray production. While the exact mechanisms of charge production were debated, the machine functioned through electrostatic induction as the disks rotated, building up large voltages and charges that could produce sparks or power other devices.

1. The Wimshurst Influence
Machine
by Ben Merritt

2. Outline
• Overview of Machine
– Sectors/Disks
– Neutralizing
Brushes
– Charge collectors
– Leyden Jars
– Electrodes
•How the Machine
Functions
•Use with X-Ray Tubes
•James Wimshurst

3. James
Wimshurst
• WasaBritish inventor, engineer,
shipwright. Born in 1832.
• Electrical influencemachinesgained
hisattention in 1878.
• Mademany of thepreviousmachines
already in existence; also modified
them to createintermediateforms.
• By 1883 created what isnow known
astheWimshurst InfluenceMachine.
• Never patented, but machines
becameassociated with hisname.

4. The Machine
• Themachineitself iscomposed of
several parts. Namely:
– Two counter-rotating disks
(including sectors)
– Neutralizing brushes
– Chargecollectors
– Leyden jars
– Dischargeelectrodes

5. The
Machine
• Two counter-rotating disks
– Allow for electrical potential/induction
– Must beascloseaspossibleto allow for electrostatic induction between
sectors
• Must bemadeout of non-conducting material
– Thusonly sectorscan conduct, hold charge
– Glass, plastic
• Generally moresectors= better performance
– Sectorsdistributeelectric field moreeffectively
Disks & Sectors

6. Neutralizing Brushes
• Two pairsof neutralizing brushes
• Don’t actually “neutralize”; simply
allow for induction to occur
between platesin contact (or
chargeflow depending on theory)
• Makephysical contact with the
sectors.
The
Machine

7. Charge Collectors
• Theseareableto absorb or drop
electronsfrom passing sectors
– Theresulting chargeiscarried
into external circuit (Leyden jars)
• Alwaysaresharp, thin points
• Never in contact with disk;
however, ascloseaspossible
The
Machine

8. Why must the charge collectors be
Sharp?
• Sharp pointshaveastronger
electric field for two reasons:
– They haveahigher surfacearea
per acertain volumecompared to
flat or rounded objects. Thus
they can createastronger EF.
– Chargesnaturally enjoy moving
to points
• So actual exchangeof e- occurs
between combsand sectors; must
havestrong EF, high EF density.

9. Why must the charge collectors be
sharp?
• All electronsin a
conductor want to be
positioned so net
force= 0
• They then accumulate
on apoint so asto
accomplish this
• Higher density of
charges= stronger EF
…resultsin…

10. Leyden Jars
• Simpleform of capacitor
• Collect built up chargefrom
collector combs, allowing for
largevoltage
• Inner foil contact induces
oppositechargeon outer, with
both capacitorshaving
reversed chargesfrom each
other.
The
Machine

11. Leyden Jars and Dielectrics
• Dielectricsaregenerally
non-conducting materials
(plastics, glass, etc.)
• However theatomspolarize
in EF.
• ThiscreatesaEF from the
atom in theopposite
direction, cancelling the
opposing EF to adegree.
• Thusgreater charge at a
lower voltage, increasing
capacitance
Polarization diagram
Effect in capacitor
• E = V/d : ↓E, keep d constant, V
decreases.
• Thus C= Q/V ; ↓V, ↑C.

12. Capacitance in my Jars
• Polycarbonatematerial
used asdielectric
• Certain permittivity value
(dielectric constant) in
relation to vacuum
permittivity constant (ε0)
• In thiscase εr=3.
• Greater permittivity
meansgreater polarization
and thusresistanceto EF.
C = εrε0 A/d
C= 3(8 .8 5x1 0-1 2
)(0.01 7 1 53) /
(4x1 0-4
)
A = πDL
A= π(.042)(.1 3)
A= 0.01 7 1 53 m2
C= 1 .1 38 53 x 1 0-9
F
o r
C= 1 ,1 39 pF
________________________________

13. Electrostatic Induction
• No chargesgained/lost
– Objectsmaintain overall
electrical neutrality
• Simply rearrangement of
electrons
• Coulomb’sLaw
• Critical to performanceof
Wimshurst machine

14. So How Does it Work?
• Video
• Start with small
chargeimbalance
• Inducesopposite
chargeon other plate
at brush; brush
inducesopposite
chargeon other side
of plate.
• Chargesbuilt up are
collected at combs
until max voltage
reached

15. What?
• Exact method
furiously debated;
problem with extra
charge. From
wheredoesit
come??
• From theair?
• Variety of methods
and theories
developed, still
rather fuzzy.
Most likely result of
tinkering and gradual
evolution of
machines
“ Existing theo ries o n the
actio n o f electro static
influence machines are
no to rio usly insufficient”
(Jo hnso n 51 ).

16. Discharge Electrodes
• EF and voltageincredibly
hugebetween electrodes
• Oncepolarization of
moleculesin air hasreached
limit, resultsin dielectric
breakdown
• Essentially ionization
• Gasionizesand then
current flows
• Light from recombination,
collisions(smack)
The
Machine

17. How Much Voltage?
• Dielectric strength of
air = ~3MV/m
• Thusif spark gap of
1cm, needs30,000Vto
createspark.
• Greater voltagesof
coursepossiblefor
better machines
Can calculateother stuff:
Uc = 0.5CV2
Uc = 0.5(1 .1 38 x1 0-9
)(30,0002
)
Q=CV
Q = (1 .1 38 x1 0-9
)(30,000)
_________________________
Q = 3.41 4 x 1 0-5
C
Uc = 0.51 21 J

18. • Wimshurst machineshad been
used earlier in the20th
century
to produceX-raysfor medical
purposes.
• Obviously thehigh voltage
allowsfor high energy
photons.
Use with X-Ray Tubes
_______________________________
qV= 0.5mv2
= hf
qV=hc/λ → λ = hc/qV
λ = (1.99x10-25
) / (1.6x10-19
)(30,000)
λ = 4.15 x 10-11
m
or 0.0415nm

19. Bibliography
• Clipper Controls Inc. “Dielectric Values.” <http://clippercontrols.com/pages/dielectric-values#P>
(June 5, 2010).
• de Queiroz, Antonio. “Operation of the Wimshurst Machine.” <http://www.coe.ufrj.br/~acmq/wh yhow.html> (May 30, 2010).
• Elert, Glenn. “Dielectrics.” <http://physics.info/dielectrics/> (June 7, 2010).
• __________. “Dielectric Strength of Air.” <http://hypertextbook.com/facts/2000/AliceHong.sht ml> (June 6, 2010).
• Holladay, April. “Why Charge Accumulates, and the Field is Strongest, on Pointed Ends of Conductors.”
<http://weatherquesting.com/sharp-points-why-charges-pack-into.htm> (June 4, 2010).
• Johnson, V.E. Modern High-Speed Influence Machines. London: 1922.
• Kuruts, Ron. “Electrostatic Induction.” <http://www.school-for-champions.com/science/static_in duction.htm> (June 7, 2010).
• Spiritus-Temporis.com. “James Wimshurst.” <http://www.spiritus-temporis.com/james-wimshur st/biography.html> (June 5, 2010).
• Springer, Matt. “Electric Charge and Sharp Points.” <http://scienceblogs.com/builtonfacts/2009/
06/yesterday_we_dumped_a_bucket.php> (June 3, 2010).
• von Slatt, Jake. “Jake's Wimshurst Machine and How to Build It!” <http://steampunkworkshop.c om/how-build-wimshurst-influence-
machine-part-1> (May 25, 2010).