Magnetism(Review)

Magnetic Field Lines always move out of the __________end of a magnet! A.East B.North C.South D.West

Magnetic Field Lines always move into the __________end of a magnet! A.East B.North C.South D.West

Where are all magnets the strongest? A.At the North Pole B.At the South Pole C.At both Poles D.Directly in the center

Magnets can be made of iron, _________, or nickel. A.Copper B.Carbon C.Cobalt D.Cadmium

Two similar poles of a bar magnet will always _____________. A. attract B. repel

Two opposite poles of a bar magnet will always _____________. A. attract B. repel

Electromagnetism -- the relationship b/w electricity and magnetism

Hans Christian Oersted Is there a relationship between electricity and magnetism? Let’s see what I discovered!!!

Oersted’s Law The flow of electricity through a wire conductor produces a magnetic field around the wire.

Right Hand Rule The direction of the current determines the direction of the magnetic field.

Can anything affect the strength of a magnetic field?

2 things affect the strength of a magnetic field: Amount of current – Increase current = increase strength – Decrease current = decrease strength # of coils of wire – More turns of wire = more strength – Less turns of wire = less strength

What did you find out? I was just wondering what would happen if I slammed an iron core through a current carrying coil of wire?

If you take an iron core and insert it into a coil of current carrying wire, you have a temporary magnet called an electromagnet!!

Strength of an Electromagnet 2 things affect the strength of an electromagnet(same 2 things that affect the strength of a magnetic field): 1.Amount of Current 2.# of turns of wire(# of coils )

What happens to the strength of an electromagnet if the current through the wire increases from 4 A to 9 A? A.Remains the same B.Increases C.Decreases

Which electromagnet will be the strongest? A B

Uses of Electromagnets Electric Meters: because of their ability to detect current(only work when there is one), electromagnets are used in a variety of electric meters. 1.Ammeter—measures current Wired in series 2.Voltmeter—measures voltage Wired in parallel 3.Galvonometer—”detects” current

Uses of electromagnets(cont.) Motors – Use electromagnets to convert electrical energy into mechanical energy – An electromagnet turns inside a permanent magnet

Motors

If current moving through a wire produces a magnetic field, I wonder …… ….What would happen if we move a wire through a magnetic field

I bet it has never been tested. Let’s try it!!! I’ll try anything once!!

Joseph Henry Michael Faraday Haven’t we already done that?

Faraday and Henry discovered that moving a wire through a magnetic field, or moving a magnetic field through a coil of wire “induced” a current on the wire!! Electromagnetic Induction— process in which moving a wire through a magnetic field produces a current on the wire.

….produces a current on a wire. “Did we just “create” electricity” Generators—use electromagnets to convert mechanical energy into electrical energy.

Generators

Other Uses of electromagnets: Transformers Not this Kind!!!! Are you talking about me?

Alternating vs. Direct Current Alternating Current Current alternates, one direction, then the other. Direct Current Current only goes in one direction. Plug it in, Plug it in!!

Transformers Used to increase or decrease the voltage of alternating currents.

Transformers Consist of 2 coils of wire. – Primary Coil Alternating current enters – Secondary Coil Alternating current leaves It’s the difference in the number of turns of wire on each coil that causes the voltage the change.

2 Types of Transformers Step-up Transformer – Increase voltage – Secondary more turns than primary Step-down Transformer – Decrease voltage – Primary more turns than secondary

Math of a Transformer:

A step-up transformer has 400 turns on its primary coil and 600 turns on its secondary coil. If the primary coil is supplied with 120 V of alternating current, what will be the secondary (output) voltage? n s = 600 turns n p = 400 turns V s = ? V p = 120

Example #2

Example #3