Problem No 4

Problema chardepen 1. The Let us Soap f

Figure 1 Soap m

Form Dec Dec

Also, tcauses In somthe glysoap fbecom 2. The Now leused: • A v

prov• Elec• Diffe

soap• A m

one • A die• Diffe

diffe

m: Create rged bodyds on the

e Soap Film

start invefilm is form

1. Soap film

molecules m the surfarease the rease the

his differes a very int

me of our ecerin decreilm. So, des more e

e experime

et us des

oltage souvides 27 00ctrodes of derent distap film;

metal loop and not grelectric looerent sign oerent result

I.Vekua

a soap fily is placed

position a

m Structur

estigation omed by sur

structure.

play the imace structuevaporatiosurface ten

nce in theteresting p

experimenteases the ue to the lastic.

ental Setup

scribe our

urce - an00 Volts; different fonces betw

(frame) forounded; op (frame);of body chts !!!).

Alexand4 (2010). “SOAP FILM”

Phys-Math der BAR

( s.barnschool No 4

RNAVELI

lm in a cird next to iand natur

re

of this prorface active

soapfigurSoanegNegtheyBetwions

mportant roure of soapon of waternsion.

e positive ahenomeno

ts we addewater evapglycerin a

p

r experime

old CRT

orms; ween the el

r the soap

; arge (and

naveli@gma42. Tbilisi, GGEORGIA ail.com )

rcular wiret. Investig

re of the ch

e loop. Thgate how tharge.

e soap filmthe shape

m deformsof the so

s when oap film

blem by ce agents (p moleculere).

ap molecuative C17H

gative iony form surween two ls.

ole in the filp film; r;

and the neon, which w

ed a small poration fro

a soap film

ental setu

T monitor,

ectrodes a

p film - gro

d this gave

considering(Surfactantes, betwee

le is dividH35COO -

s collect orface struclayers of fi

lm formatio

egative ionwill be disc

amount oom the sur

m gets an

p. We

which

and the

ounded

g the soapts). There

en which th

p film strucare two la

here is wat

cture [1]. ayers of ter (see

ded into pions.

positive NNa+ and

on the sucture.

rface of film and

lm there are water and Na+

on. They:

n distributiocussed belo

on in a soow.

oap film

of glycerin rface and a"extra dur

to soap, balso stabiliration of lif

because zes the fe" and

Figure 2. EExperimentaal setup.

3. A spWe begspheric

pherical c

It was o– As la

the l– In th

defofilm

– For Film

Let us by the equatiocalculasurfaceQ and loop ra

From tfollowin

nd tha e

This fo

gan experical charged

harged bo

observed, arger the less the infhe case oormation inremained the small

m continued

explain thisurface t

on while tated using e tension fd. We will

adius and t

the Figureng values:

e effective

orce must b

iments withd body and

ody

that: distance dfluence (de

of d~5 cmn the centestable; d~h, the

d to stretch

is theoretictension forthe electro

an "electforces we use the ahe distanc

e 4 the co

electrosta

be balance

h an interad a soap fi

d between eformation

m, the heiger was ab

stable stah, discharg

cally. In surce. The lostatic forcrostatic imcan calculpproximati

ce to the ch

ndition of

;

tic interact

ed by the s

action betwlm.

sphere ann); ght h of bout 1 cm

ate did noe develope

ch interactatter can ce betwee

mage methate the deion, when harged sph

Electr• Thecharg• The• Thethe "effecbetwe• Thecharg• We

seg• AC • Q –

d>>• q’

distφ = φC B

tion force w

urface tens

ween a

nd film -

the film and the

ot occur. ed and film

tion the elebe calcula

en the chhod". Equaependencethe deform

here. ric force. e externaes on the fe film surfae interactiogrounded

ctively" preeen the twoe value ae must giv

e assume gment ABC

– the loop– the exter>h

– the "tance x fro= 0 (a g

will be:

sion force.

m explodedd. FFigure 3.

ectrostatic ated by marge and

ating the Ce of h on thmation is m

force is bameans of L

the film Coulomb ahe sphere

much less t

alanced Laplace can be and the charge

han the

al field rfilm;

redistributees the

ace is equaon betwee

sphere esented ao point cha

al-potentia

nd the plave equipote

n the charfilm ca

s the intearges;

l; rge and an be eraction

that the

ace of "efential film sfilm is a

ffective" surface; sphere

C of the hep (frame) ornal charge

"effective" om the loopgrounded f

ight h of a radius ae, at the d

a. distance

at the charge p. film) leadss

,

.

to the

(1)

(2)

SurfaceUsing t

we obt

If we w

alanB c

Using t

is qIt u

when hexperimequatio

here

Figure

w

5The dep Let us Fl incrsituatioexplod

e tension fthe Laplac

ain

write down

ce of Electrthe force e

uite a comph << a ; hments wasons (1),(2),

x ≈ 2h –

from we ge

5. pendence h(

make somreases withon is opposes.

force. ce formula P

Fl = pS , w

rostatic andequilibrium

plicated forh = a = Rs small co,(4) get the

– d ; q’

et the depe

(d) for the s

me notes. Fh h faster site - Fk in

Pl = 4σ0 /

we will get

d Surface condition

rmula, so tR. We canompared te form:

≈ -Q ;

endence o

stable states

From the (3than Fk.

ncreases w

R and takking into acccount, thaat

the fthat o

tension forFk=Fl for

to make it n do it for oo the fram

F = kQ

of on h Q a

Let's caldependenFor a 1cpotential φQ = Cφ =Noting thad = 5 cmquite nea

s: (experime

3) and (2):So the sta

with h fast

.

orce of the .

.

surface te

ension is

rcesd (3

. (2) an )

clearer, leour case, sme radius.

Q2/(4d)2 ;

and : d

·

culate hnce is givecm radiusφ = 27 00= 4πε0r· φ at σ0 ≈ 25

m from (6)r to our ex

ent - points;

Fl ~ h ; Fable equiliber than Fl

) we get:

.

et us use thsince the f. In this a

kQ2 = 3

for our en on the gs charged

00 v, we ge≈ 3 · 10-8

· 10-3 n/m) we get hxperimenta

theory - c

Fk ~ 1/(d-hbrium is rel , so the f

he approxi

(3)

(4)

mation,

film stretchapproximat

32π hd2

h in our tion the

, (5)

·

experimen

. (6)

nraph.

d sphere,

t. This

at the et: Coulomb

m, for the db.

h ≈ 1 cm,l results.

distance that is

urve).

h) . If h <2 <eached. If film stretch

< d, the h ~ d,

hes and

4. A flaBy thdeform

at chargedhe f

becausHowevthe filmthat ca 6. An aTo obtparallegroundvoltageon a plthe filmIn the negativ 7. InteIn this but thewind frof a "hwind", strengtattractiElectricof charthe caelectricat the bmolecuThey mentiocausedthe folfilm wparticleacceler 8. Inte

char In

oth pthis

battractithe "dip

lat d body

mation wase the fieldver withoum was sigase the ions

approximatain the ul large li

ded while e was applastic (diele

m did not ststrong fielve charges

eraction ofcase the s

e dip was from abovehill") was ca

which bleth was gron. c wind takrge on these of nail

c field neabottom of tules and sthit the fil

oned dip. Td by charglowing ex

we placed es and it rated partic

eraction ofrged body

case the rocesses -on towardsp" and the

charged s larger

d was stront groundingnificantly s could not

ately unifouniform fieids. The

to the tied. The filectric) looptretch, dued the film

s.

f film with soap film dformed, as. The obseaused by ew rather reater than

kes place e electrode-type sharr it is verythe nail poltrongly replm and fo

The fact thged particleperiment. the detefixed a l

cles.

f film with y.

served ob- the elects electrode"hill" are fo

body th(see Fig

nger. ng the str

less becat “leave” th

orm fieldeld we us

bottom ltop lid thlm was for

p. In the une to the forc

simply wa

charged ndid not stres if there berved dip (so called "

strong an the stre

when the e is very hirp electrody strong. Tlarizes the

pels the eleorm the

hat this wines we provInstead octor of charge amo

small-hea

behavior rtric wind ae. Both – ormed.

he film gure 6)

retch of ause in he film.

sed two id was

he high rmed niform fieldce symmetas torn by

nail. etch out, blew the (instead "electric

and this ength of

density igh (like de) and

The field air

ectrons. above-

nd was ved by

of soap harged

ount of

aded

reveals and the

try. the forces

s acting on

S

Small-hea

FFlat charge

n the posit

FSharp-ende

Figure 6. ed body.

ive and

Figure 7. d body. e

Faded charge

Figure 8. ed body.

9. Thechan

e asymmet

As we article, the negcausesIt tookpoles, seems and no In our hangc e

the bodof discof sparthe elewas chspreadelectrodischar What isAt highelectroFrequethe train atomconstalight. Iemits bluish- that whthe ligh(which is emitt The Nacceleremissionegativand ca In the lm. Tfi h

yellowattractestructudischar

nge of potry with reespect to the

mentionedthe differe

gative ion s a very ink place wi.e. the chto be the

ow let’s car

experimee of the pody) affects harge on trk are depeectrode chharged pod and yeode was rge was bl

s the reasoh temperatomagnetic ency of emnsition ene

m: EPhoton=nt, and ν It is knowyellow liglilac light.

hen electroht is emitteare prese

ted by Sod

Negative erated electon. Also, ve externaause the str

case of phese ions

w color of ed by the re and arerge becom

les. d in the beence in thedistributio

nteresting when we arge sign

e most interefully cons

ents we ooles (i.e. cthe shape

he soap filendent on harge. Whsitively, d

ellow, whcharged

luish and

on of this? tures the a

waves mitted lightergy betwe

=hν, where- frequen

wn, that Sght, whileThus we c

ode is chared by the atnt in air) w

dium (Na)

external ctrons strikein this cal body, moraight form

positive exhit the filmdischarge negative e more or

mes more "

ginning of e positive n in soap phenomenchanged of the boderesting resider it.

observed, charge signe and the cm. Paramethe sign ofhen electrdischarge wile when

negativstraight.

atoms emit(photo

t dependseen two leve h – is Plancy of emiSodium (N Nitrogencan conclurged negattoms of Ni

while in theatoms. Wh

charge ace the Nitr

ase the poove freely tm of discha

xternal chm and pun. Besides,ions of s

r less “spre"spread" (h

this and film

non. the y. It

esult

that n of

color eters f Disrode was the

vely,

the ons). s on vels

anck tted

(Na) n - de ively

D

Nitrogen e case of phy it is so?

ccelerates rogen atomositive Na+

owards therge.

harge heavnch out of in this ca

soap (thesead-fixed” here we se

scharge (ye

Discharge (b

positively?

the electrms of air a+ ions in e point nea

vy ions of it the pos

ase the pse negativ

around thee the cha

llow). Positi

F

blue). Negat

charged e

rons towaand cause soap are

arest to it,

air acceleitive Na+ iunched oue ions for

he film surarge shape

ively chargeigure 9. Fd body. e

Figure 10. ively charge

ed body. e

electrode, tthe light

ard the filmtheir bluis

m. The

attracted concentrat

erate towa

sh-lilac

ions which

by the te there

ards the

ut Na+ iorm the sorface areae asymme

h cause ons are oap film ). Thus try with

respect to pole sign. It is caused by the soap film ionic structure – different “flaw freedom” degree of the positive and the negative ions). In this case we also saw that most upper part of the spark is blue, while the main yellow region is under the level which can be reached by the punched out Na+ ions. 10. Conclusion. In this work we studied the soap film interactions with the charged bodies. The

the charged bodies were tested and the resulting film eformations were examined

ich the film is formed ture

Also, a very interesting phenomenon of the discharge asymmetry with respect to the ch structure pro

voltage.

p Bubbles. Dover Publications, NY 1992.

different shapes ofdWe found out that film deformation strongly depends on:

– The shape of the charged body – The charge value– The distance from the film – The grounding of the loop on wh– The soap film struc

ange of poles was observed. We explained it by the specific ionicperties of a soap film.

Finally I want to thank my grandfather Tengiz Barnaveli for his help in the experiments with the high References

] Cyril Isenberg. The science of Soap Films and Soa[1