Electricity and Magnetism
Dec 26, 2015
Electricity and Magnetism
Atomic Review
An atom consists of 3 particles:
Protons-positively chargedNeutrons-no chargeElectrons-negatively
charged
What is Electricity?
• A form of energy caused by moving electrons.
How charges act
Like charges repel Opposite charges attract.Electrons flow from a
negatively charged area to a positively charged area.
Most objects are electrically neutral
Static Electricity
•Static means “stuck in one place.”•Static Electricity that doesn’t “flow” like the electricity in your house.•It builds up and “discharges” like when …
Phenomena
Lightning strikes You slide across a car seat and
touch the door handle. Ben Franklin and his kite. Sliding your feet on a rug and
touching the doorknob. Rubbing a balloon on your hair
and sticking it to the wall
How are charges transferred?
When you rub two substances together you do work and thus you add energy.
This removes electrons from one substance and adds it to the other.
This creates IONS which are charged particles.
Summary
The energy used to rub two things together is the
energy that gets involved in removing and
transferring electrons.
Electrical Charge
Can be Transferred.
It cannot be created or destroyed.
Conductors
A conductor allows charges to flow easily
Some conductors are better than others Examples: Copper Iron
Insulators
An insulator prevents electric charges from flowing easily
Examples:Rubber CorkWood Plastic
Electric Current
Electric Current is the flow of electrons through a conductor
There are two types of electric current: Alternating Current Direct Current
Alternating Current
Changes direction at a regular rate Most commonly used type of
electricity because it does not create as much heatExamples:Appliances HousesChristmas lights
Direct Current
Always flows in one direction Always flows from negative to
positive
Example:Battery
Creates a lot of heat
What is a Battery?
A series of electrochemical cells Two types:
A wet cellA dry cell
Wet cell
Electrolyte (a conducting material) is a liquid Example:Car battery
Dry cell
Electrolyte is a moist pasteExample:AA battery
What is a circuit?
The path an electric current follows Consists of four parts:
Source Load
Wires Switch
Current flows only through a closed circuit
Diagrams
Source Resistance
Lamp Motor
Wire
Switch
What is a series circuit?
A circuit where current follows only one path
If one light goes out, the whole circuit goes out
Diagram of a Series Circuit
What is a parallel circuit?
Current follows more than one path If one light goes out, the others
remain on. Used in:
HomesSchoolsBuildings
Diagram of a Parallel Circuit
Circuit diagrams are a pictorial way of showing circuits. Electricians and engineers draw circuit diagrams to
help them design the actual circuits. Here is an example of a parallel
circuit.
What are volts? Electromotive force (EMF) is the force
that moves electrons in a circuit. A volt is the unit used to measure EMF.
What are amps?
The amount of current depends on the number of electrons flowing in the circuit.
An ampere (amp) is the unit used to measure current.
What are ohms?
Resistance opposes the flow of electrons in a circuit.
Resistance of a wire depends on length, thickness, material, and temperature.
An ohm is the unit used to measure resistance.
Magnetism
Where do magnets come from?
Iron can be made into magnets
3 things stick to magnets iron, nickel, cobalt (the Iron Triad)
Magnetic Pole
A pole is the area of the magnet where the magnetic effect is the strongest.
One pole of the magnet will always point north this is the north pole.
The south pole will point south. The north and south poles are
unlike and therefore attract.
Magnetism
MagneticFields
Magnetic Fields
Exist in regions surrounding magnets.
Exerts a torque on a compass needle. (Demo)
Compass needles allow us to map out magnetic fields.
Magnetic field lines flow out of the north pole and into the south pole.
They are continuous and never cross
The Earth itself is a magnet!
Earth’s magnetic field causes compasses to line up.
Magnetic north/south pole is about 11º off from geographic north/south pole.
Why?
Scientists are not sure why the Earth is a giant magnet but some believe that it is due to the circulation of molten metal (iron and nickel) within the Earth’s core.
Oersted’s Discovery!
The presence of an electric current in a wire causes a torque in a compass nearby.
A current carrying wire generates a magnetic field.
Electromagnetism.
Electric Current
The flow of charge through a material
The amount of charge that passes through the wire in a unit of time is the rate at which the
electric current flows. The unit of current is the ampere or amp.
An electric current produces a magnetic field.
the rule of thumb: the direction of the current determines the direction of the magnetic field in a current carrying wire.
Cause
All magnetism is caused by the movement of charges.
Electromagnet
An electromagnet is a strong magnet that can be turned on and off.
Increase strength
You can increase the strength of an electromagnet by:
-Increasing the current-Increasing the number of loops of
wire to the solenoid.-Wind the coils of a solenoid closer
together.-Use stronger ferromagnetic material
for the core.