Types of Circuits

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What is the difference between the wiring?

Series Circuits

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The light bulbs turn on.

However, since the voltage drops, the lights are dimmer.

1 V

0.5 V

Battery is 1.5 V

Series Circuits

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If this light bulb does not turn on,If this light bulb does not turn on,

neither light bulb neither light bulb will turn on.will turn on.

This is because the circuit is broken here;

so the current can’t flow to this bulb here.

Burned out light bulb

Battery is 1.5 V

Christmas lights are commonly made this way.

Series Circuits Info•The current has only one path it can travel along

•One light goes out all lights out-open circuit •Imagine if you turned off one light in your house that means that the circuit is broke and everything else goes off. Everything would have to be turned on to keep things running.

•Current is the same at all points•Voltage is reduced by each resistance (light bulb, motor, heaters)

•Voltage drop-each separate resistor causes volts to drop

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Kirchhoff’s Voltage Law

•The total of all voltage drops must add up to the total voltage supplied by the battery. (energy in)

•+1.5 V - 0.5V - 0.5 V - 0.5 V = 0battery bulb bulb bulb

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Parallel Circuits

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- - aa divideddivided circuit and the current has more than onecircuit and the current has more than one pathpath..

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Parallel Circuits

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When one light bulb When one light bulb burns outburns out the others still the others still light uplight up..

Even though the path is stopped, the other light turns on because its circuit is not broken.

Burned out light bulb

Your house is wired with parallel circuits.Your house is wired with parallel circuits.Why do you think this is so?Why do you think this is so?

Parallel Circuit Info

•contains separate branches for current to move through

•potential difference (volts) same at each branch•one light off, use other branches to transfer current

•voltage is the same across all branch points (think of them as separate series circuits connected to a battery)

•each branch does NOT always have the same current, depends on how much resistance is in each branch, (desk lamp, power saw) 8

Kirchoff’s Current Law

•If current flows into a branching point, the same total current must flow out again.

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MAGNETISM

• property of matter in which there is a force of attraction or repulsion between unlike or like poles.

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MAGNETIC MATERIALS1. Permanent magnet

•material that keeps its magnetic properties, even when it is not close to other magnets

•Magnetite = natural magnetic rock (Lodestone)

•Ex. bar magnet, refrigerator magnet, horseshoe magnet

2. Temporary magnet•easy to magnetize, quick to lose

magnetism•nickel, cobalt, iron, eg. AlNiCo (alloy)

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Common Properties of Magnets

• Two opposite poles called north and south

• If divided, there will always be a north and south pole

• When near each other, magnets exert magnetic forces on each other

• OPPOSITE POLES ATTRACT; LIKE POLES REPEL

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Magnetic Domains•Domains-groups of atoms with aligned magnetic poles•Electrons in atoms behave like small loops of current that act like tiny electromagnets with north and south poles•We don’t see the magnetism because it is so small and on average the atomic magnets cancel each other out•When atoms are aligned in a similar direction a permanent magnet is produced•Atoms in iron, cobalt, and nickel are free to move - If brought near a permanent magnet it forces the atoms to temporarily align and therefore becomes a temporary magnet•In nonmagnetic materials the atoms are not free to move so they are not affected by magnets

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Magnetic Domains

unmagnetized

magnetized

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Auroras• NORTHERN &

SOUTHERN LIGHTS

• Produced by the earth’s magnetic field trapping charged particles from the sun.

• The particles collide producing light.

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Losing Magnetic Properties

Magnets lose their magnetic properties if alignment of the domains is destroyed.

Alignment can be destroyed by:

1. dropping the magnet

2. heating the magnet

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Magnetic Fields

• The force felt around the area of the magnet• Magnetic field lines – represent the direction of

the field around a magnet; Arrows are drawn north to south

• Number of field lines represents the strength of the magnet in that area

• The force is the strongest at the poles

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Discovering Magnetism

•  500 B.C. – people discover naturally occurring materials have magnetic properties (lodestone which is magnetite)

• 500 B.C. – Greeks noticed one end of suspended lodestone pointed north and the other pointed south, first application of the compass

• 220 B.C. – Chinese also recorded use of compass called “south pointer”

• 1088 A.D. – Chinese made small needle like compass

• 1183 A.D. – modern compass appears

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Compass

Compass needle is a magnet free to spin until it lines up in the north-south direction

Geographic north pole of the Earth is the magnetic south pole since it attracts the north poles of the magnet

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EARTH’S MAGNETIC FIELD

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Do you know where the North Pole Is?

Wandering PoleWhile the Magnetic Pole often skips around many miles each day in an oval loop, on average it migrates from 6 to 25 miles each year to the north/northwest.

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Movement of the Pole

• During the sixteenth century, mariners believed that somewhere in the North was a magnetic mountain that was the source of attraction for compasses.

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ELECTROMAGNETISM

• Hans Christian Oersted – Danish physicist and chemist who discovered that a current in a wire caused a compass needle to deflect

• Moving electric charges create a magnetic field

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Electromagnet•Magnets that are created when there is electric current flowing in a wire

 Simplest electromagnet uses a coil of wire, often wrapped around some iron

 Iron core becomes a magnet

 Magnetic field aligns with the coil carrying current

 North and south poles are located at the end of each coil

 Which end is north depends on the direction of the electric current (North is where the current comes out)

 A good electromagnet is a balance between too much resistance and having enough coils to get a strong magnet

•Uses of electromagnets – speakers, doorbell, toaster

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ELECTROMAGNET

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INCREASING THE STRENGTH

1)   increase size of iron core2)   increase current3) increase the number of coils

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ELECTROMAGNETIC INDUCTION

• 1831 - Michael Faraday(UK) & Joseph Henry(USA) • process by which moving a wire through a magnetic

field an electric current is induced in that wire • If a magnet is thrust into a coil it induces current

flow• If the magnet stops the current stops• The quicker the movement of the magnet the more

current induced• When you pull the magnet back out the current

flows in the opposite direction• Electromagnetic induction is how we transform

mechanical energy into electrical energy• Power plants use generators

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• Generators change mechanical energy to electrical energy

• Electric motors changes electrical energy into mechanical energy

• Commutator-reversing switch in a motor that rotates with an electromagnet

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ELECTRIC MOTOR

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GENERATOR

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• Transformers: step-up (increase) or step-down (decrease) voltage

• MRI-magnetic resonance imaging-magnetic field taking pictures of your insides

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MRI uses radio waves and a magnetic field to produce images of

the body

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Electrical Measuring Instruments

• Voltmeter-used in parallel to measure voltage

• Ammeter-used in series to measure current

• Galvanometer-use to detect a current

New uses for magnetism

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