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# Electricity & Magnetism PowerPoint PPT Presentation

Electricity & Magnetism. Universal Forces Throughout all galaxies far, far away………. Remember, FORCES exert a push or pull on objects and can do WORK They can act over a distance without touching Gravitational force – a weak force due to mass

Electricity & Magnetism

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## Electricity & Magnetism

### Universal ForcesThroughout all galaxies far, far away………

• Remember, FORCES exert a push or pull on objects and can do WORK

• They can act over a distance without touching

• Gravitational force – a weak force due to mass

• Electromagnetic force – a stronger force due to charged particles

• ELECTRICITY

• MAGNETISM

### What is a charge?

• All matter is made up of atoms

• All atoms are made up of :

• Protons (+)

• Neutron ( 0)

• Electrons (-)

• Electrons extremely SMALL mass

• travels extremely FAST

• has A LOT of KINETIC energy !

### What is a charge?

• Atoms are normally NEUTRAL because:

# of PROTONS = # of ELECTRONS

• Electrons can move easily between objects

• When an object LOSES electrons  positively charged

# of PROTONS > # of ELECTRONS

• When an object GAINS electrons  negatively charged

# of PROTONS < # of ELECTRONS

• This movement of electrons can transfer energy and do WORK.

+

-

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+

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+

+

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-

NEGATIVE

POSITIVE

### Law of Charges

• Like charges REPEL or PUSH (+ and +) OR ( - and -)

• Unlike charges ATTRACT or PULL (+ and - )

• FORCE is exerted by electric charges!

### Check for Understanding:Would the following repel or attract each other?

• REPEL

• ATTRACT

• REPEL

-

-

and

-

+

and

+

+

and

• Electrons (-) push each other away

• Electrons (-) are pulled toward protons (+) or other positively charged objects

### Induction

• Some objects that really have an equal amount of charges, can temporarily shift their electrons so that an area may become more positive or negatively charged.

### Static Electricity

• Charges that build up is called static electricity.

• Pollution control systems to capture smoke particles

• Photocopiers, speakers, microphones

• Lightning

• Muscle cells

• However, in general, static electricity is a nuisance!

• Van der Graaf and Rockin’ Bill Nye

### Static discharge

• Discharge is a sudden movement of electrons

• Unpredictable

• Unreliable

• Its just not really useful.

• Static discharge occurs when a new path forms between two areas of opposite charge.

• The electrons move suddenly to try to restore the balance between charged areas.

### Electric Current

• Static discharge is brief and limited in the number of electrons it moves.

• To do USEFUL WORK, we need a continuous flow of charge.

• This is an electric current.

### Electric Current, Cont.

• For an Electric Current, we need…

• A steady supply of moving electrons

• A path for the electrons to follow and return to be reused.

• Something to “push” the electrons along the path.

### Water Analogy

• Water in a high reservoir (PE) causes a downward force through pipes to a lower reservoir.

• The higher the reservoir, the higher the PE.

• Water flows through pipes in a continuous path. Higher reservoir creates flow with more KE.

• Water is pumped back up to the higher reservoir to be re-used.

### The electric circuit…

• Electrons “flow” along a closed path with no breaks.

• Battery chemicals provide the “push” of electrons, acting as a “pump”. (ELECTRICAL FORCE )

• The “strength” of the battery provides the PE of the circuit.

Work is done as electrons flow through a circuit .

### Circuit Construction

• pHet Circuit Construction interactive

### Let’s talk numbers!

• A battery is a device that converts chemical energy to electrical energy.

• In a battery , one terminal (end) is Positive and the other terminal (end) is Negative.

• The PE of the electrical flow of electrons from one end to the other is the voltage of the battery.

• Higher voltage = Higher “push” of electrons through the circuit (Joules/Coulomb)

### Let’s talk numbers!

• Coulomb (C)

• Is a bunch of electrons (6.25X 1018 electrons)

6,250,000,000,000,000,000 electrons

• 1 Volt is the PE that can move 1 Coulomb of charge using 1 Joule of energy

• Ampere(amps) is 1 Coulomb in one second ( C / s)

### What if we add…a water wheel ?

• A wheel would hinder the flow – like friction.

• Water uses some of it’s energy to make the wheel turn (work)

• Water flows on through the wheel to continue the flow.

• More than one wheel could be put into the flow of water.

### Resistors

• Resistor = any object or substance that slows down the flow of electrons.

• Electrons transfersome of their Kinetic energy when going through a resistor, so this is a place of energy conversion:

• Light bulb  light energy

• Heating element  thermal energy

• Speaker  sound energy

• Resistance measured in ohms. (Ω)

• ### A short circuit:

• Resistors also protect a circuit from becoming a SHORT CIRCUIT!

• Too much current!!

• Wires get HOT!

• Plastic covering can melt.

• Fire may start.

• Drains battery fast – or flips protective circuit breakerin electrical panel.

### Magnetism

• Early discovery of natural occurring lodestones

• they always oriented themselves north when floated on a piece of wood on water and

• they concentrated iron shavings

• There are Naturally occurring magnets and Man-made magnets.

• Current science understands magnets to ALWAYS have a NORTH and a SOUTH pole, no matter how many times you divide a magnet(Di-Pole)

### Effects of Magnetism

• Magnetic fields show the strength and direction of magnetic forces.

• Closer lines = more strength

• Force lines point from north pole to south pole

• Same poles REPEL

• Opposite poles ATTRACT

• Effects of magnetism is very similar to the effects of static electrical charges.

### Magnetism from Electricity

• Magnets attract only a small group of materials.

• Iron, nickel, cobalt, steel

• We can INDUCE magnetism in some materials, especially iron.

• A wire carrying a current that is coiled around a metal core strengthens the magnetic field.

• The more coils, the STRONGER the magnetic field (lab!)

• Electromagnets = magnets created by use of electric current.

Li nk

### Electricity from Magnetism

• Does this work the other way around?

• YES! If a magnet is moved through a coil of wire, a current is produced in the wire.

• pHet Faraday interactive

• What did you notice about the current flow?

• The current only flows when the magnet is moving! When the magnet stops moving, so does the current.

• The magnet PULLS the electrons along through the wire.

• The more quickly the magnet moves, the faster the electrons move, SO….more current.

• Remember… current is more electrons per second

• More work is being done!