Electricity and Magnetism

Atomic Review An atom consists of 3 particles:  Protons-positively charged  Neutrons-no charge  Electrons-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: RubberCork WoodPlastic

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 heat Examples: Appliances Houses Christmas 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 cell A dry cell

Wet cell  Electrolyte (a conducting material) is a liquid Example: Car battery

Dry cell  Electrolyte is a moist paste Example: AA battery

What is a circuit?  The path an electric current follows  Consists of four parts: SourceLoad WiresSwitch  Current flows only through a closed circuit

Diagrams  Source Resistance  LampMotor  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: Homes Schools Buildings

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 Magnetic Fields

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.