Download Electrostatics

Electrostatics
Electrostatics
● The branch of science
dealing with static
charges and their
electric fields
● The Greek word for
amber, ήλεκτρον
electron, was the
source of the word
'electricity'
A little history
● The science of electricity has its roots in
observation, known in 600 BC that a piece of
amber rubbed with animal fur would attract
straw, feathers
● Thales of Miletos (Greece) in credited with
this discovery
A quick review of the atom
●
Every atom has a
______ charged
nucleus surrounded by
____ charged
electrons.
●_______ move in and out
of fixed pathways around
the nucleus
●
positively
negatively
Electrons
Charges
● Two kinds: positive
and negative (terms
coined by Benjamin
Franklin)
● Like charges ________
● Unlike charges ______
repel
attract
Static Electricity
What is amber?
● Amber is the fossilized
form of tree resin…not
the same as sap.
● Resin is similar to our
scabs. It flows out of
the tree to plug a hole.
The Leyden Jar
● Progress quickened
after the Leyden jar
was invented in 1745
● The Leyden jar stored
electricity and
therefore could be
studied at length
Benjamin Franklin
● 1752
● By tying a key onto a
kite string during a
storm, Ben Franklin ,
proved that static
electricity and
lightning were the
same.
The Battery
● A new interest in current began with the invention of
the battery. Luigi Galvani had noticed (1786) that a
discharge of static electricity made a frog's leg jerk.
● Galvani thought the leg supplied electricity, but
Alessandro Volta thought otherwise. He showed that
the metal plate and the Leyden jar were different
metals and produced a current. He built the voltaic pile,
an early type of battery, as proof.
Of the 3 types of subatomic particles,
which one can move?
● Electrons in the (outer, inner) rings or shells of atoms
are bound more loosely to the nucleus
● Such electrons tend to break free from the nucleus and
wander around amongst other nearby atoms
● Such electrons are called free electrons
Insulators and Conductors
● Different materials hold electrons
differently.
● Insulators don’t let electrons move around
within the material freely.
○
Ex. Cloth, Plastic, Glass, Wood, Rubber
● Conductors do let electrons move around
within the material freely.
○
Ex. Metals- Silver, Copper, Aluminum, Gold
Objects that tend to give up electrons
and become positive:
● Glass
● Fur
● Hair
● Wool
Objects that tend to attract
electrons and become negative:
• Rubber
• Styrofoam
What happens to your hair when you
rub a balloon on your head?
● The balloon, after being
rubbed and then pulled
away, removes some of the
electrons in your hair
which give each strand a
positive charge. Like
charges want to repel and
each strand is repelling
from the others and
“sticking up.”
Let’s review
Salt and Pepper
Let’s review
#4
Water and
balloon
Review
If an object is +3 what does that mean?
It has a net charge of +3
Draw your picture
If an object is -2 what does that mean?
It has a net charge of -2
Draw your picture
Review
How can a neutral object become negative?
Gains electrons
How can a neutral object become positive?
Loses electrons
Charges..symbol is “q”
There are several “laws of conservation”;
1)Mass
2)Energy
3)Momentum
4)Angular momentum (spin)
5)Charge
Law of Conservation of Charge
Charges within a closed system may be
transferred from one object to another, but
charge is neither created nor destroyed.
So how does a battery run out of energy?
What is a force field?
Force Field
▪ Definition- The area that
exists around a mass, electric
charge or magnet, so that
another object will experience
a force
▪ http://www.telegraph.co.uk/technology/news/7487740
/Star-Trek-style-force-field-armour-being-developedGeneral, Organic, and Biological Chemistry
Copyright © 2010 Pearson Education, Inc.
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by-military-scientists.html
Electrostatic Force
● This is a non-contact force (like the gravitational force
except instead of two masses exerting force on each
other the two objects charges exert a force of
repulsion or attraction).
Electrostatic Force Fields...NOT force at
a distance
Be glad you are not a cat
Coulomb’s Law-formula for electrostatic force
Again this is similar
to the gravitational force…
Fg = GmM
r2
charge (q) is now
responsible for the force
Fe = kq1q2
r2
Just like G was a constant so is k.
k is the electrostatic constant
and = 8.99 x 109 N•m2/C2
Fe = kq1q2
r2
Fe
r2
Coulomb’s Law Practice
micro, nano, pico
µ
n
p
E-6
E-9
E-12
Million billion trillion
Worksheet