Download Electricity and Magnetism

Electricity and Magnetism
12/27/2007
REMEMBER THE PARTS OF AN
ATOM??
• Protons ( positive)
• Neutrons ( neutral )
• Electrons ( negative )
The force that holds a nucleus together is called an
ELECTROMAGNETIC or STRONG FORCE
Normally…..
• Normally the electrons and protons are
equal to BALANCE the charges in the
atom.
• IF atom gains or loses electrons to
become stable than it is CHARGED.
• Gaining electrons makes an atom
NEGATIVELY charged and LOSING
electrons makes them POSITIVELY
CHARGED.
How can we charge an atom?
• AGAIN..Atoms can be charged by
GAINING or LOSING electrons.
• Remember ( forming ions occurs when
atoms are gained or lost through chemical
reactions)
• THERE ARE OTHER WAYS TO GAIN OR
LOSE ELECTRONS.
What are electrical CHARGES?
•
These occur when a charge is GAINED
or LOST through TRANSFERRING
ELECTRONS by
1. Friction – rubbing
2. Induction – bringing a charge object near
an neutral object
3. Conduction – flowing through direct
contact ( this is sometimes called
transfer through CONTACT)
Unlike the situation where like
dissolves like …
This is because the surrounded by an ELECTRICAL FIELD
What is static electricity?
• This occurs can occur
when friction transfers
ELECTRONS from
one object to
ANOTHER.
• The shock you feel
occurs when the
electrons are
transferred from your
hand to the KNOB.
Examples:
1. Like the shoes rubbing against the
carpet. Electrons are transferred from the
carpet to the shoes.
2. Rubbing a balloon on your
shirt…electrons are transferred from your
shirt to the balloon.
3. When you remove clothes from the
clothes dryer some have gained electrons
and some have lost them. They will stick
together.
More examples
• . Electrons move from your hair to the hat.
Now each of the hairs has the same
positive charge.The farthest they can get
is to stand up and away from all the other
hairs.
How does lightning occur?
Positively
charged
particles are
moved to the
top of the
cloud and
negatively
charged
particles are
moved to the
bottom of the
cloud.
What is a A Van der Graaf ?
How does an electroscope
work?
• An ELECTROSCOPE
is device used to
detect a static charge.
• An positive of
negative charge on
both leaves will cause
the leaves to REPEL
and move away from
each other.
Which way will the balls move and
why
What is the difference between static
electricity and current electricity?
STATIC electricity is stationary or collects on the
surface of an object,
CURRENT electricity flows THROUGH A CONDUCTOR
How are good conductors different
from poor conductors?
• Good conductors – metals especially
copper which is commonly used in
electrical wires.
• Poor conductors / resistors – they slow but
do not stop the flow of electrons.
• Insulators – they STOP electrical flow.
How are voltage current and
resistance related?
voltage (electric potential) is flowing through
the wires of the circuit. (V). It is similar to the
buildup of water in the previous picture.
THE CURRENT is measured in Amperes (A).
Resistance (R) is the opposition to the flow of an
electric current, causing the electrical energy to
be converted to thermal energy or light
(measured in ohms) (Ω).
V= I R
Understanding resistance …..
Ohm’s Law calculations…
How a lightbulb works…
The metal which makes up a
light bulb filament or stovetop
eye has a high electrical
resistance. This causes light
and heat to be given off.
How does a battery work?
Batteries are composed of a chemical substance which
can generate voltage which can be used in a circuit.
What are the Parts of an electrical
circuit?
voltage source ( BATTERY) , a wire conductor, and one
or more devices which use the electrical energy (ie
lightbulb) .
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.
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.
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.
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 module – 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
What is magnetism?
Magnetism is the properties and interactions of
magnets
The Magnets produce magnetic forces and have
magnetic field lines
Magnets have two poles…Unlike poles
attract and like poles repel….
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.
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.
The MORE COILS THE GREATER
STRENGTH
What is a Galvanometer?
A galvanometer is an electromagnet that interacts with a
permanent magnet.
The greater the current passing through the wires, the stronger
the galvanometer interacts with the permanent magnet.
What are electric motors?
An electric motor is a device which changes electrical
energy into mechanical energy.
How does an electric motor work?
What is electromagnetic induction?
Moving a loop of wire through a magnetic field produces
an electric current. This is electromagnetic induction.
Direct current versus alternating current
Direct current is electrical current which comes from a
battery which supplies a constant flow of electricity in
one direction.
Alternating current is electrical current which comes
from a generator. As the electromagnet is rotated in the
permanent magnet the direction of the current alternates
once for every revolution.
What happens to the water
from a garden hose when the
water is turned on, and there
is a hole in the hose?
What does this have to do
with electricity?
What is
electricity?
What is the difference
•Between a
longitudinal and
transverse waves
Please Write down all the
equations for electricity!
Project!
• You will create a diagram of the electricity
in one of the rooms in your home!
• Please make sure you use correct
symbols.
• You will also need to calculate the
electricity in one of your rooms.
• a) Draw a circuit with one bulb
and one cell as you would see it
in ‘real life’.
• b) Now draw the same circuit,
but use symbols to represent
the different
components.
WARM UP:
If my computer has a resistance
of 22 ohms draws a current of
5.0 Amperes, what is the power
of my computer?
• Current(I) (in amps) = Voltage (V) (in volts)
I = V or V=I x R
• Resistance(R) (in ohms) R
• Power(Watts) = Voltage(volts) X
Current(amperes)
• What current flows through a hair dryer
plugged into a 110 Volt circuit if it has a
resistance of 25 ohms?
A 12 Volt car battery pushes
charge through the headlight
circuit resistance of 10 ohms.
How
much power is being used?
A heater in a house uses 1500
Watts of power. If the circuit is
110 Volts, what is the current
through the heater?