Post on 13-Mar-2018
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.
• 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
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