Static Electricity

What is Static Electricity• The buildup of electrical charges in one place.

• Static = charge does not move or flow

• (usually a temporary condition).

• Can be detected by an electroscope.

The leaves are repelled by the like charge upon them.

• Remember, only electrons move!

• If a +ve rod is near the electroscope,

electrons are attracted to the top

• This leaves a +ve charge on the leafs and

they separate

• The opposite is also true:

• If a -ve rod is near the electroscope,

electrons are repelled to the bottom

• This leaves a +ve charge on the top and a –

ve charge on the leaves �they separate

Examples of static electricity:• Rubbing a balloon on your hair

• Walking across carpet

• Clothes tumbling in dryer

• What do these have in common?

Friction!!!!

Creating Static Charges

• Static charges result when some charges

are transferred from one object to another

by friction

• Which charges are easily removed?

– Recall structure of the atom.

Recall from Chemistry

• Electrons (-) are on the outside of the atom

so they can be easily removed, while

protons (+) are held firmly in the nucleus

• Protons & Neutrons

• Electrons

Two Types of Charge

• Electrons can be transferred by friction, but

protons cannot

– Transferring protons would create a new element!

• LOSING electrons gives an object a POSITIVE

charge

• GAINING electrons gives an object a

NEGATIVE charge

• NOTE: When one object loses, another must

gain - electrons can’t be created or destroyed

Combing

transfers

electrons from

the hair to the

comb by

friction,

resulting in a

negative

charge on the

comb and a

positive

charge on the

hair.

BEFORE

AFTER

Induced charge

• Charged and neutral objects (not touching)

are attracted because electrons move in the

neutral object.

• Electrons move toward a +ve charged

object and away from a –ve charged one.

• This is called “induced charge”

– See Fig. 3.8

Conduction

• Conduction = direct transfer of charge

• Eg: walk across carpet and touch a

doorknob � shocking!

• Electrons are stripped from the carpet and

you gain a net –ve charge

• When you touch the doorknob, electrons

jump onto it � electrical discharge

Neutral and

neutral

-ve and –ve

-ve and

neutral

+ve and +ve

+ve and

neutral

+ve and -ve

NeitherRepelAttract

Place an “X” in the appropriate box:

XNeutral and

neutral

X-ve and –ve

X-ve and

neutral

X+ve and +ve

X+ve and

neutral

X+ve and -ve

NeitherRepelAttract

Place an “X” in the appropriate box:

Rules of static electricity

1. Objects with like charges repel, but

objects with unlike charges attract

2. Charged objects attract neutral objects

Does friction always create

static charge?

• Different materials have different strength

of attraction for electrons

• If two objects of the same material are

rubbed, no static charge forms

• (equal number of electrons transfer each

way)

• If two different objects are rubbed, they

will have different attraction to the

electrons. The stronger one will take

electrons away from weaker one and

static charges build up

• E.g. glass rod and silk cloth

– Silk has stronger attraction to electrons, so

it removes some from glass

– Glass becomes +vely charged (silk would

have -ve charge)

• E.g. Amber rod rubbed with fur

– Amber has a stronger pull on electrons

so it will remove some from fur

– Amber becomes negatively charged

(fur becomes +ve)

• In labs we usually use plastic strips

• Acetate (clear) - positive charge

• Vinyl (white) - negative charge

Uses of static electricity

• Trapping particles in smokestacks of factories

• Applying grit to sandpaper

• Spray painting mesh (e.g. chain link fence)

• Powder coating

Fun with the Van de Graaff generator

• http://en.wikipedia.org/wiki/Van_de_Graaff_generator

Homework:

• Page 46, questions 1 to 6

• Page 49, questions 1 to 6

Act 3C Effects of Static Charges

(Formal Report)• Purpose -write your own, (based on

questions on p. 44)

• Materials - refer to . . . .

• Procedure - refer to . . . .

• Observations - copy/complete table on p.45

• Discussion - Answer questions 1 - 3 (full

sentences)

• Conclusion - comment on lab referring to

purpose