9.1 STATIC ELECTRICITY
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Electricity involves the movement of electrons
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Electrons are incredibly small, have almost no mass, have a charge of –1 and can
be removed from atoms quite easily
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There are two different types of electricity
1. STATIC – a charge that stays on an object and does not move, unless it comes
into contact with another object
2. CURRENT – a charge that flows from one place to another (i.e. around a circuit)
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2 types of charge:
1. POSITIVE – results from a net LOSS of electrons
2. NEGATIVE – results from a net GAIN of electrons
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Do neutral objects have charges?
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Can neutral objects become charged?
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YES – the negative and positive charges on a neutral object are EQUAL to one
another ( the charges are BALANCED)
YES! – rubbing two neutral objects together (called CHARGING BY FRICTION)
causes the movement of electrons
One object will lose electrons and will therefore become positively charged
The other object will gain electrons and will therefore become negatively charged
How can we tell which object becomes positive and which one becomes negative
(without doing an experiment!)?
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Use the ELECTROSTATIC SERIES (a list of common objects describing how ell
they hold on to their electrons)
Weak hold on electrons
( become positive when rubbed)
acetate
glass
wool
cat’s fur/human hair
calcium/magnesium/lead
silk
aluminum/zinc
paraffin wax
Strong hold on electrons
(become negative when rubbed)
ebonite
polyethylene (plastic)
carbon/copper/nickel
rubber
sulfur
platinum/gold
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When 2 substances are rubbed together, the one HIGHER in the series always
LOSES electrons (and becomes positively charged) while the one LOWER in the
series always GAINS electrons (and becomes negatively charged)
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LAW OF ATTRACTION AND REPULSION
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LIKE charges always REPEL
OPPOSITE charges always ATTRACT
NEUTRAL objects are ATTRACTED by CHARGED objects
Why does a charged object attract a neutral object?
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I.e. if all of the charges in a neutral object are balanced, why then does the
charged object attract it? Does the neutral object gain or lose charge?
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NO!!! – the charged object pulls the opposite charges in the neutral object so that
the charges in the object are rearranged
Neutral piece of paper
Positively charged glass rod
When the two objects are brought close together, the charges in the paper rearrange
themselves so that most of the negative charges move closer to the positive charges
in the rod. This creates a more negative charge on the side of the paper closest to
the glass rod, which allows the two objects to be attracted to one another
Force of attraction
between the two objects