1dphys - pp4 (static electricity)

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SNC1DPHYSICS

THE CHARACTERISTICS OF ELECTRICITY

L Static Electricity

(P.396,421-423)

Static Electricity

What do lightning and a photocopier have in common? How about thatunexpected “zap” when you reach for a doorknob or your hair mysteriouslystanding on end after pulling off a wool hat on a winter day?

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Static Electricity

Objects can become charged when electrons move from one object toanother. The electric charge that builds up on the surface of the object iscalled a static charge or static electricity. The charges are “static”because they remain very nearly fixed in one location on the surface of theobject until they are given a path to escape.


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Static Electricity

For example, the girl below is touching a van de Graff generator – itgenerates static electric charge. The student’s hair shows what canhappen when static electricity builds up on someone touching thegenerator. Each strand of hair has the same static charge. This makes thestrands of hair repel one another and spread out as far as possible.


Static Electricity

The accumulation of even larger numbers ofelectric charges can lead to some impressiveelectrical displays – lightning for example. Thelarge, bright flashes of lightning are the sameas the small electric sparks you may have seenwhen touching a doorknob or taking off asweater – they are just different in size.


Static Electricity

RECALL!

If a neutral object obtains extra electrons, the object becomes negativelycharged. If a neutral object loses electrons, the object becomes positivelycharged.

STATIC CHARGE or STATIC ELECTRICITY

� electric charge that builds up on the surface of an object

� caused by a transfer of electrons

� charge remains fixed in place (ie “static”)


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Static Electricity

PRACTICE

1. Why might a plastic rod that contains a large number of electrons nothave a static charge?

because the rod is neutral (i.e. the #e = #p)


Uses of Static Electricity

Most of the time we think of static electricity as an annoyance. It makesour hair look messy and can make our clothes stick together. However,scientists and engineers can use the properties of static charges in manyuseful ways in a branch of science called electrostatics. Electrostatics isthe branch of science that deals with static charges and static electricity.

ELECTROSTATICS

� the study of static electric charges



PRACTICE

2. Name four applications that use electrostatic principles.


Administrator

Typewritten Text

Stop Here!

Administrator

Typewritten Text

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Advertisers use static-cling vinyl filmfor brightly coloured removable signs,decals, and stickers like the one shown.The windows of many homes, officebuildings, and cars are covered with filtersthat screen out sunlight. These screensuse static electricity to cling to thewindow.



PRACTICE

3. Explain why it is not a good idea totry to put up static-cling decals on avery humid day.

humid air = no static charge (watermolecules in air remove excesscharge)



Electrostatic paint sprayers usethe properties of static charges tomore efficiently paint objects. Thepaint is given a charge as it leavesthe nozzle of the sprayer, and theobject to be painted is given theopposite charge. The chargedpaint particles are attracted to theobject, which minimizes theamount of wasted paint andensures that the object receives aneven coat of paint.


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Electrostatic precipitators usethe properties of static charges toclean the air. Before the gas from afactory is released it is sent throughpipes that charge the tiny particlesof pollutants, called particulates,negatively. The gas then movesthrough an area that has positivelycharged plates which attract thenegative particles and remove themfrom the gas. Precipitators use verylittle electricity and can removeabout 99% of the particles insmokestack emissions.



Photocopiers also use the properties of static charges to work.Photocopiers convert an image captured by a scanner into a laser beam.This beam is projected onto a drum or belt, creating a negatively chargedpattern (a). The positively charged ink, called toner, is attracted to thenegative charges in the image (b). As negatively charged paper movespast the drum, the positively charged toner particles are transferred to thepaper (c). The paper than passes through a fuser that melts the tonerparticles onto the paper.



USES OF …

� static electricity has many practical applications including:

• static-cling vinyl film (removable signs, stickers, …)

• electrostatic sprayer (reduces the amount of wasted paint)

• electrostatic precipitator (cleans the air)

• photocopier


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U Check Your Learning

1. Why does someone’s hair stand on end when they are touching a vande Graaf generator that is running?

creates the same static charge on each strand of hair – this makes thestrands of hair repel one another and spread out as far as possible

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2. Explain how eliminating staticelectricity would hinder theperformance of an electrostaticpaint sprayer.

no static charge = no attraction(i.e. the paint would just pass byso you would have to rotate theobject to completely coat it)



3. How can neutral pollutantparticles be made attractive tothe charged plate in anelectrostatic precipitator?

give the neutral particles acharge before they enter theprecipitator


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4. Sometimes, finished photocopied paper will stick to you. Explain why.

the paper is still charged from the photocopying process



TEXTBOOK

P.403 Q.6

P.426 Q.5,6,8,14


1dphys - pp4 (static electricity)

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