DL-Magnetism

Demo - Basic Magnets - What the North Pole of a magnet means. I float a magnet on a petri dish, and it will turn toward the North with surprising robustitude, robustness, robustidy.

Demo - Basic Magnets - How to use a compass to determine the polarity of a magnet. (Bring the unknown magnet in from the side, and see which pole of the compass needle likes it)

Demo - Basic Magnets - The Direction of a Magnetic Field. I use a magnaprobe (a magnet on a gimbal) to show that magnetic field is from N to S.

Demo - Basic Magnets - Magnetic FIeld Lines. A plastic block with oil and iron filings shows the field lines looping around. (As they always do)

Demo - Force on a Current Carrying Wire. I put a bundle of wire carrying about 150 Amps total in between the poles of a magnet (5A in 30 windings) , and have the students predict the direction of the force on the wire given the direction of the current, and the direction of the magnetic field. It works. Yay Physics!

Demo - Magnetizing an Iron Bar with a Hammer. I put on hearing protection and eye protection, and beat on an iron bar that is pointed parallel to the earth's magnetic field. The domains will line up and the end pointed North becomes a North Pole magnet. I show them what pole the taped end of the bar is before I beat on it, and show them that it has changed after I have beaten on it for a couple of minutes. I then reverse it and magnetize it back the way it was. This bar lives in the bottom of the Magnet cupboard.

Demo - Magnetizing a Screwdriver with a Really Dodgy Solenoid. I connect a big air core solenoid to a power strip (That plugged into a wall socket - so look out!), and compete the circuit with a thin strip of aluminum foil. When I turn on the power strip, the foil fuse blows, but not before re-arranging the magnetic domains in the screwdriver. The screwdriver can now pick up a paperclip. Then I put the screwdriver into a stout small solenoid connected to a variable output AC power supply. I turn it up until I can feel the screwdriver shaking, and gradually turn down the AC voltage to zero - the domains in the screwdriver will drop out randomly, leaving it un-magnetized, and unable to pick up the paperclip. Be super careful - I both unplug the solenoid, and turn off the power strip. If I am feeling at all spacy, I get a student to be a safety monitor, and make sure I don't touch the solenoid connections without unplugging it from the power strip. That would be bad.

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Demo - Generators - I use the hand crank generators to light up a light bulb, but also to show that the crank is harder to turn when it is connected to the light bulb as opposed to being connected to nothing. I put a dead short on the generator and it is even harder to turn. I talk about how electric cars brake (almost never with just friction - they use the motor to charge the batteries - which is only one reason you shouldn't charge to 100%)

For fun I attach the generators to each other and show that the generator is a motor too. You can estimate the efficiency of the conversion - turn the crank 10 times, and have them count the number of revolutions of the the driven motor.

Demo - Induction - Induce a current with a coil and a magnet, and predict the direction the current will flow

Demo - Transformers - Different kinds of transformers - Show and tell.

Demo - Two Coil Induction - I talk about how people initially assumed that a constant magnetic field should cause a current to flow. I switch the inner coil on and off, and turn the current up and down, all the while not looking at the meter. The important thing is that ir is a change in magnetic field that creates a current. - and only while the change is occurring.

Demo - Faraday's Law ILDs. This is a Sokoloff ILD modified slightly to make it like many IB test questions. The students make solo predictions, then as a group discuss a group prediction. I have them put their predictions on a slide show of their own, and I also have group slide shows that they make their group predictions on.

Website: Faraday's Law ILD

Lab - The Magnaprobe Lab - this is a cute station lab with a lot of the demo stuff we use and more. Little questions. Fun.

Video for: Long Long Solenoid .:. Flat Solenoid/Wire

Lab - The Magnet Design Lab. Students design an experiment (usually involving a Hall Effect probe)

Here is the Website: Magnet Design Lab

Lab - The Specific Heat of Water. Students determine the specific heat of water using a Voltmeter, an Ohm Meter, a Thermometer, a graduated cylinder, and somewhat surprisingly, an electric hot pot.

Lab - Faraday's Law PhET - A very excellent PhET lets the kids predict and then try to explain the direction of induced currents when you move a magnet close to an easy to interpret virtual coil of wire.

Lab - Faraday's Law Video Quiz - This is from Sokoloff's book. There are 4 videos, and the students must determine which video goes with which graph of voltage or current. It's cute and fun.

(Note the suggested videos)

Lab - stuff

Demo - stuff

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