Electricity & Magnetism

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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

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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.
Check for UnderstandingWhat would occur to make a positive or negative particle?

+

-

-

+

+

+

-

-

+

+

-

-

-

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
• 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.