Chpt 25 – Magnetism and Electromagnetic Induction Broadneck Physics Electromagnetism and ElectroMagnetic Induction

Chpt 25 – Magnetism and Electromagnetic Induction Iron filings dropped onto a piece of paper below a magnet will demonstrate the magnetic field lines If you break a magnet, each piece will establish a N and S pole!

Chpt 25 – Magnetism and Electromagnetic Induction Placing a magnet in an existing magnetic field produces a torque (a twist!) on the magnet if it isn’t aligned with the field.

Chpt 25 – Magnetism and Electromagnetic Induction Opposite poles nearest to each other Similar poles nearest to each other We get a more complicated pattern with two magnets!

Chpt 25 – Magnetism and Electromagnetic Induction We believe magnetism is caused by our old friends – electrons – as they both spin on their axis and rotate about the nucleus.

Chpt 25 – Magnetism and Electromagnetic Induction

The magnetic field of an individual iron atom is so strong that interactions among adjacent atoms cause large clusters of them to line up – these clusters are called magnetic domains. This iron is NOT magnetized. The domains are randomly arranged!

Chpt 25 – Magnetism and Electromagnetic Induction But if we subject this iron to a strong magnetic field, it will become magnetized. The domains will “line up”.

Chpt 25 – Magnetism and Electromagnetic Induction

Wai Tsan plays with magnets…! (actually, nails which have been temporarily magnetized). Wai Tsan is one cool dude…

Chpt 25 – Magnetism and Electromagnetic Induction Electrical current – the flow of electrons – produces a magnetic field. There is a fundamental connection between electricity and magnetism!

Chpt 25 – Magnetism and Electromagnetic Induction Current (I) Current moving through a wire “induces” a magnetic field about the wire.

Chpt 25 – Magnetism and Electromagnetic Induction We can use our iron filings to show this…!

Chpt 25 – Magnetism and Electromagnetic Induction Ceramic superconductors can produce extremely strong magnetic fields because the magnetic field cannot penetrate into the ceramic materials. Suspended magnet! “Maglev” trainMaglev

Chpt 25 – Magnetism and Electromagnetic Induction Magnetic Forces on Moving Charges A magnetic field can change the direction of an electron beam

Chpt 25 – Magnetism and Electromagnetic Induction The Earth’s magnetic field deflects many harmful high- energy charged particles.

Chpt 25 – Magnetism and Electromagnetic Induction Engineers designing high-voltage power towers have to worry about the forces of the Earth’s magnetic field on the large currents being carried in the wires!

Chpt 25 – Magnetism and Electromagnetic Induction Since the flow of electricity produces magnetism, we should be able to use a magnet and a coil of wire to test for the presence (and the amount of!) electrical currents.

Chpt 25 – Magnetism and Electromagnetic Induction The same basic device – called a “Galvanometer” – is the basis for meters which test for current, voltage and resistance in circuits!

Chpt 25 – Magnetism and Electromagnetic Induction An Ammeter measures Current. It lets a small % of the current flow through the Galvanometer. The Voltmeter has high internal resistance, so it just senses the electrical “pressure”

Chpt 25 – Magnetism and Electromagnetic Induction Electric Motors The current moving through the wire induces a magnetic field, which is attracted & repelled by the magnetic field from the big magnet.

Chpt 25 – Magnetism and Electromagnetic Induction

MRI machine MRI visualization of a ruptured spinal disk

Chpt 25 – Magnetism and Electromagnetic Induction Magnetic Induction Moving a current through a wire causes a magnetic field to be formed. So…does moving a magnetic field past a wire cause a current to be formed??? The answer is YES! Lots of things in physics (and nature!) work this way…

Chpt 25 – Magnetism and Electromagnetic Induction Moving the magnet (and thus its field!) inside the coil of wire will induce a current, which we measure with the meter

Chpt 25 – Magnetism and Electromagnetic Induction It doesn’t matter whether the wire moves past the magnet, or the magnet past the wire. It’s the relative motion of one to the other which induces the current.

Chpt 25 – Magnetism and Electromagnetic Induction And the more wires we have “intercepting” the magnetic field, the more current we get!

Chpt 25 – Magnetism and Electromagnetic Induction Mr. Faraday stated this another way: “The induced voltage in a coil is proportional to the number of loops, multiplied by the rate at which the magnetic field changes within those loops.” So are we producing voltage or current…?

Chpt 25 – Magnetism and Electromagnetic Induction Electric Guitars The metal guitar string – slightly magnetized – induces a current in the coil!

Chpt 25 – Magnetism and Electromagnetic Induction Generators and Alternating Current It is easier to move the wire (or coil of wire) than it is to move the magnet. If we do this we produce current that changes direction with each turn.

Chpt 25 – Magnetism and Electromagnetic Induction A graph of the current vs. time….

Chpt 25 – Magnetism and Electromagnetic Induction NEWS FLASH !! Generators do not “produce” energy... They change one type of energy (mechanical) into another type (electrical), and only with about 60% efficiency

Chpt 25 – Magnetism and Electromagnetic Induction A power plant converts thermal energy to steam to mechanical energy to electrical energy…

Chpt 25 – Magnetism and Electromagnetic Induction Since the current direction is changing 60 times per second in AC current, the associated magnetic field is constantly changing as well. Wires wrapped around a conductor will induce a current in that conductor as this happens. Nothing has to “move”… Recall the amount of current produced depends on the number of wires wrapped around it!

Chpt 25 – Magnetism and Electromagnetic Induction The ratio of the input side (primary) turns to the output side (secondary) turns tells us how much the voltage is decreased or increased!

Chpt 25 – Magnetism and Electromagnetic Induction The iron “core” help to focus the magnetic field.

Chpt 25 – Magnetism and Electromagnetic Induction You are here! Power Grid

Chpt 25 – Magnetism and Electromagnetic Induction Or another view…

Chpt 25 – Magnetism and Electromagnetic Induction Complicated controls in a nuclear plant!