Download Electricity Notes

Electricity Notes
Electricity Part A
• All matter is composed of atoms.
• Atoms are made up of smaller particles
called protons, neutrons, and electrons.
• Protons are positively charged and electrons
are negatively charged.
• According to the law of electric charges, like
charges repel and opposite charges attract.
• If an atom loses electrons it becomes
positively charged. If an atom gains
electrons it becomes negatively charged.
There are three ways to “charge” an object...
1. Conduction– e- are transferred by direct contact
Ex) uncharged metal & + charged glass rod
(e- travel from metal to glass rod leaving the metal +
charged)
2. Induction- when charges in an uncharged object
are rearranged w/o direct contact
Ex) – charged balloon and neutral wall
(+ charged object near a neutral object and e- in
neutral object are attracted to + charged object
& move towards it)
3. Friction- when two objects are rubbed together
electrons are “wiped” from one to another
Ex) rub a plastic ruler with a cloth
(e- are transferred from the cloth to the ruler)
Charge can be detected by using an Electroscope.
Ex) Glass flask with a metal rod inserted through a rubber stopper.
There are two metals leaves at the bottom of the rod.
Leaves hang straight down when not charged and move apart when charged.
Uncharged
Charged
Static Electricity
• Static – not moving
• Static electricity is the build up of charges
on an object.
• The charges that create static electricity do
not move away from the object they are
stuck to.
Why do clothes stick together after they
are taken out of the dryer?
When you dry clothes in the dryer,
different fabrics rub together, and
electrons from a cotton sock (for
instance) may rub off onto a polyester
shirt. That's why clothes sometimes
stick together and make sparks when
you pull them apart.
How does a fabric softener (dryer sheet) work
to prevent static cling?
As these sheets bounce around with your
clothes, they add a uniform antistatic
coating to the fabric. Rather than cotton
rubbing against polyester, you've got the
antistatic coating on the cotton rubbing
against the antistatic coating on the
polyester. No electrons rub off and you
don't get any static cling.
• The loss of static electricity is discharge.
• Gradually, over time, charges that build up on an
object leave the object.
• Electric discharge may happen rapidly or slowly.
• The most dramatic example of electric discharge is
lightning.
Current Electricity
• Electric current is a continuous flow of electrons.
• Current is how fast charge passes at a given point.
• There are 2 types of electric current: Alternating
Current (AC) and Direct Current (DC).
• Electric current produced by batteries is DC and
electric current from your home outlet is AC.
• Current in a wire is determined by voltage
and resistance. The higher the voltage, the
more energy is released.
• Resistance is the opposition to the flow of
electric charge.
• It is represented with the symbol
http://electronicsclub.info/circuitsymbols.ht
m
• The higher the resistance, the less current
is in it.
• Resistance can change depending on an
object’s material, thickness, length, and
temperature.
• An example of a material that has a low
resistance is copper.
• Iron is a good conductor.
• Materials with a low resistance are used to
make wires.
• A thick pipe has less resistance because
there are more spaces for current to travel
through.
• A thin pipe has more resistance because it
does not have to move around many spaces.
• In general, resistance increases as the
temperature of a metal increases.
• This happens because atoms move faster at higher
temperatures and get in the way of electric charge.
• If you cool certain materials, resistance will drop
to zero.
• These materials are known as superconductors.
• They can be useful because very little energy is
wasted when current travels through them.
Comparing Electricity & Magnetism
Electricity
Magnetism
+ and – Charges
North and South Poles
Like Charges Repel
Like Poles Repel
Unlike Charges Attract
Unlike Poles Attract
electric field lines flow from + to -
magnetic field lines flow N to S