Transcript Electricity

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True or false:
1. ELECTRONS FLOW AT NEARLY THE SPEED
OF LIGHT?
2. BATTERIES & GENERATORS CREATE
ELECTRICITY?
3. ELECTRICITY LEAVES ONE BATTERY
PLATE, THEN RETURNS TO THE OTHER?
5. TOO BAD FRANKLIN SAID ELECTRONS
ARE NEGATIVE?
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6. "ELECTRICITY" IS A PHENOMENON
COMPOSED OF ENERGY?
7. ELECTRICITY IS MADE OF ELECTRONS?
8. STATIC ELECTRICITY IS THE OPPOSITE OF
CURRENT ELECTRICITY?
9. EACH INDIVIDUAL ELECTRON CARRIES
ENERGY?
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10. ATOMS HAVE EQUAL NUMBERS OF
ELECTRONS AND PROTONS?
11. CONDUCTORS ALLOW CHARGE TO PASS?
12. ELECTRICITY IS WEIGHTLESS?
14. "ELECTRICITY" IS A FORM OF ENERGY?
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Law of Electric
Charges: Like
charges repel and
opposites attract.
Protons – positive
Electrons- Negative
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Electric Force: The
force between two
charged objects
Electric Field – force
created by charged
particles
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Conductor - a material
which contains
movable electric
charges
Insulator – a material
which doesn’t contain
moveable electric
charges
Conductor - like a pipe
which is already full of
water
Insulator - like a pipe
with frozen liquid; a
pipe plugged by ice
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Conservation of
charge: When you
move electrons from
one object to another
they are neither
created nor destroyed.
Static electricity is the
buildup of charges on
an object.
Electric discharge is
the release of static
electricity
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Voltage- difference
in charge between
two area’s –
Voltage is electric
potential energy
per unit charge,
measured in joules
per coulomb
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Charge flows from
area’s of high
voltage to low
voltage
Similar to the way
water flow from
high pressure to
low
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Resistance is the
tendency of a
material to resist
the flow of
electrons
All materials offer
some resistance –
conductors offer
less
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What qualities
affect resistance?
Think about a light
bulb
1. Material – W
2. Thickness
3. Length
4. Temperature
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The coulomb (C) is the standard unit of
electric charge in the International System
of Units (SI). It is a dimensionless quantity.
A quantity of 1 C is equal to approximately
6.24 x 1018, or 6.24 quintillion. In terms of
SI base units, the coulomb is the equivalent
of one ampere-second.
One coulomb is roughly equal to the
amount of charge possessed by
6,000,000,000,000,000,000 (six billion
billion) electrons. Just to give you an idea,
one coulomb is roughly the amount of
charge that flows through a 12-watt
automotive light bulb in one second.
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The flow of electrons
through wire is called
current.
Ampere or Amp- the
amount of electric
charge per second.
“Electric energy” comes
in the form of waves –
which are bound to the
electrons and protons
in the wire
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The Ampere Strikes
Back
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Ohm – named after a dude – George Simon
Ohm – if your cool he’ll be your “Ohmie”
Ohm is a measure of resistance
one ohm - one kilogram meter squared per
second cubed per ampere squared (1 kg · m2
· s3 · A2). The ohm is also the equivalent of a
volt per ampere (V/A).
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Ohm’s law
V=IxR
V = The voltage across a component
I = The current going through a component
R = The resistance of a component
R = V/I or I = V/R
Electrical Calculations – What is Ohm’s Law?
I=
3V
2Ω
I = 1.5 amps
How are static charges detected?
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DC – Direct Current
– flows in one
direction
AC- Alternating
Current – flows in
both directions
What are batteries?
Batteries are composed of a chemical substance which
can generate voltage which can be used in a circuit.
There are two kinds of batteries: dry cell and wet cell
batteries. Below is an example of a dry cell.
The zinc container of the
dry cell
contains a moist chemical
paste surrounding a carbon
rod suspended in the
middle.
Wet cell batteries are most commonly
associated with automobile batteries.
A wet cell contains two
connected plates made of
different metals or metal
compounds in a
conducting solution. Most
car batteries have a series
of six cells, each
containing lead and lead
oxide in a sulfuric acid
solution.
Bulb 1
Bulb 2
The bulbs, batteries and
wires in both figures are
similar.
Will bulb 2 shine more,
less, or equally brightly
than bulb 1?
What is the difference between an open circuit and a
closed circuit?
A closed circuit is one in which the pathway of the electrical
current is complete and unbroken.
An open circuit is one in which the pathway of the electrical
current is broken. A switch is a device in the circuit in which the
circuit can be closed (turned on) or open (turned off).
What are electric circuits?
Circuits typically contain a voltage source, a wire
conductor, and one or more devices which use the
electrical energy.
What is a series circuit?
A series circuit is one which provides a single pathway
for the current to flow. If the circuit breaks, all devices
using the circuit will fail.
If the path is broken, no
current flows through the
circuit.
What is a parallel circuit?
A parallel circuit has multiple pathways for the current to
flow. If the circuit is broken the current may pass through
other pathways and other devices will continue to work.
If one part of the path is
removed, the current
continues to flow through
the other paths of the
circuit.
How is household wiring arranged?
Most household wiring is logically designed with a
combination of parallel circuits. Electrical energy enters
the home usually at a breaker box or fuse box and
distributes the electricity through multiple circuits. A
breaker box or fuse box is a safety feature which will
open
How is Electrical Power calculated?
Electrical Power is the product of the current (I) and the
voltage (v)
The unit for electrical power is the same as that for
mechanical power in the previous chapter – the watt (W)
Example Problem: How much power is used in a circuit
which is 110 volts and has a current of 1.36 amps?
P=IV
Power = (1.36 amps) (110 V) = 150 W
How is electrical energy determined?
Electrical energy is a measure of the amount of power
used and the time of use.
Electrical energy is the product of the power and the
time.
Example problem:
E = P X time
P=IV
P = (2A) (120 V) = 240 W
E = (240 W) (4 h) = 960Wh = 0.96 kWh
◦ If magnet is moved quickly into a coil of wire, a
current is induced in the wire.
◦ If the magnet is removed from the coil, a current
is induced in the wire in the opposite direction
◦ By the same token, current can also be induced if
the magnet stays put but the coil moves toward
or away from the magnet
◦ Current is also induced if the coil rotates.
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In other words, it does not matter whether
the magnet or the coil moves. It is the
relative motion that counts.
What is magnetism?
Magnetism is the properties and interactions of
magnets
The earliest magnets were found naturally in the mineral
magnetite which is abundant the rock-type lodestone.
These magnets were used by the ancient peoples as
compasses to guide sailing vessels.
Magnets produce magnetic forces and have magnetic
field lines
Magnets have two ends or poles, called north and
south poles. At the poles of a magnet, the magnetic field
lines are closer together.
Opposite poles of magnets attract
each other and like poles of
magnets repel.
The earth is like a giant magnet!
The nickel iron core of the earth gives the earth a
magnetic field much like a bar magnet.
What are magnetic domains?
Magnetic substances like iron, cobalt, and nickel are
composed of small areas where the groups of atoms are
aligned like the poles of a magnet. These regions are
called domains. All of the domains of a magnetic
substance tend to align themselves in the same direction
when placed in a magnetic field. These domains are
typically composed of billions of atoms.
Electricity and Magnetism – how
are they related?
When an electric current passes through a wire a
magnetic field is formed.
What is an electromagnet?
When an electric current is passed through a coil of wire
wrapped around a metal core, a very strong magnetic
field is produced. This is called an electromagnet.
What is a galvanometer?
A galvanometer is an electromagnet that interacts with a
permanent magnet. The stronger the electric current
passing through the electromagnet, the more is interacts
with the permanent magnet.
Galvanometers are
used as gauges in
cars and many other
applications.
The greater the current passing through the wires, the stronger
the galvanometer interacts with the permanent magnet.
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It has been discovered by Oersted and
company in early 19th century that
◦ Magnetic field can be produced by an electric
current
◦ Magnetic field can exert force on electric charge
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So if you were scientists at that time, what
would you wonder?
◦ An American scientist Joseph Henry and an English
scientist Michael Faraday independently found that
it was possible
 Though, Faraday was given the credit since he published his
work before Henry did
 He also did a lot of detailed studies on magnetic induction
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If you allow electrons to move through a wire,
they will create a magnetic field around the
wire. Similarly, if you move a magnet near a
wire, the magnetic field will cause electrons
in the wire to move.
A generator is a simple device that moves a
magnet near a wire to create a steady flow of
electrons.
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What does a generator do?
◦ Transforms mechanical energy
into the electrical energy
◦ What does this look like?
 An inverse of an electric motor
which transforms electrical
energy to mechanical energy
• Faraday’s law of induction
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Generator is motor run backwards
Motor, generator parts are almost all the
same.
Input and output are reversed.
Apply mechanical energy to rotor (e.g. turn it
by hand), and voltage is generated in coil.