Download Electric and Magnetic Experiment 3

Experiments for my Students
Falling Objects Experiment
This uses a sheet of paper and a heavier object, like a set of car keys, shows that
heavier object don’t always fall faster than lighter objects. However, since weight is the
effect of the Earth’s gravitational field on an object, and weight is a force if the difference
in weight was the only factor in how fast an object falls that heavier objects would
always fall faster than lighter ones. Since that’s obviously not the case there must be at
least one other factor involved (inertia). The simple experimental results also indicate
that minus air resistance objects of different weights all fall at the same speed,
suggesting that this other factor is compensating rather precisely for differences in
weight. Finally, students are asked to predict the result of objects falling in a vacuum
and we then look at the youtube video of an astronaut dropping a feather and hammer
at the same time from the same height above the lunar surface. The two objects, of very
different weights, fall at exactly the same rate.
The Lever Arm Significance
In the rotational world the distance of mass from the rotation axis, the lever arm, is just
as important as how much mass is present. I give my students two bars, equal in weight
and mass but not equal in distribution of mass. I have them rotate the bars so that they
can FEEL the differences that occur.
Resonance
Students can see resonance in slinkies, water tanks, a length of pvc pipe and a simple
radio circuit and relate that to the resonance of water molecules in a microwave over or
the resonance of carbon dioxide molecules regarding infrared light as regards Global
Warming. It’s fun to follow this experiment by showing youtube video of the Tacoma
Narrows Bridge.
The Slinky Experiment
This experiment shows that waves in a slinky, because the slinky is confined between
the hands of two people, must be standing waves of quantized wavelength. This is true
of waves of any kind. I use this experiment to explain why electron waves are quantized
in wavelength and energy when confined in an atom. That, in turn, explains spectra,
much of atomic structure, energy bands in solids, why some materials conduct
electricity and some don’t and why there are semiconductors like transistors, solar cells
and LEDs.
Fun With Jello
We use Snell’s Law to calculate the speed of light in jello. We then make jello lenses of
various shapes and test whether or not laser beams trace their way through these
lenses in a way consistent with Snell’s Law. Finally, we use the jello lenses to test for
total internal reflection, the phenomenon that underlies fiber optics (we can even make
a crude fiber optic out of just jello).
I make special jello for this experiment consisting of about half the usual amount of
water and about 6 times as much jello powder. It’s very rugged.
Electric and Magnetic Experiment 1
Electric currents (moving electric charges) create magnetic fields (Ampere’s Law). You
can use electricity to make magnets. Electricity and magnetism are related.
Electric and Magnetic Experiment 2
Magnets are always dipoles (they always have two poles). Like poles repel and unlike
poles attract. This is Gauss’s Law of Magnetism.
Electric and Magnetic Experiment 3
The relative motion of magnets and coils of wire creates electricity in the wires
(Faraday’s Law). You can use magnets to make electricity.
Electric and Magnetic Experiment 4 (also an entire special test based on
experimental results)
This employs dropping strong magnets through copper pipes (you should really see
this), recording the data, working out what is going on (which is rather complicated) and
connecting the experimental results and conclusions firmly with the underlying
mathematical laws.
Electric and Magnetic Experiment 5A
This is about what a resistor is and one of its common uses.
Electric and Magnetic Experiment 5B
This is about Ohm’s Law.
Electric and Magnetic Experiment 5C
This involves how a fuse works by constructing one and burning it out.
Electric and Magnetic Experiment 5D
Finding out how junction transistors can function like a switch by constructing a circuit
containing one and switching it on and off.
Electric and Magnetic Experiment 5E
Construction of the AND logic gate using components including resistors, transistors
and LED’s. The AND logic gate is one of the basic elements used to build computers.
5 Experiments to Determine the Structure of Magnetic Fields
The first four experiments mainly serve to outline the similarity of all magnetic fields
regardless of source and what that structure is with its basic symmetry characteristic.
The final experiment consists of determining the complex magnetic field around my
magnetic track that levitates superconductors. Students can go one from this to build
their own tracks and so far two have done just that.
The Tape Experiment
This experiment uses nothing more than scotch tape to show that electric charge comes
in at least two types, causes some sort of entity called an electric field around the
charges through which the charges can exert forces on each other. Similar charges
repel each other and different charges attract. The strength of these forces increases as
the distance between the charges decreases. It’s a lot of fun to take this data and use it
to explain why building a nuclear fusion reactor is so difficult.
The Effect of Magnets on Different Materials
Materials can be roughly separated into three categories: materials that do not respond
much to magnets, materials that are attracted to magnets and materials that are both
attracted and repelled by other magnets. I have a private collection of chemical
elements that I use along with everyday objects in this experiment.
Various Magnetic Induction Experiments
These all have to do with a changing magnetic field inducing electric currents in
electrical conductors. There are many hands on ways to do this and I have built several
of my own inductor coils and cores to use in these experiments.
The Electromagnetic Pulse Experiment
This involves carting my office microwave oven into the classroom and microwaving a
little piece of aluminum foil for about a second (this is not good for the microwave,
hence the short duration of the experiment… in any case students can generalize the
sparky result to their own accidents of silverware accidently left in the microwave, etc).
What is happening is that the changing electromagnetic fields of the microwaves induce
electric currents in the aluminum foil. This is a tiny version of the EMP pulse from the
detonation of a nuclear weapon that if done from high altitude could fry electronics over
hundreds of miles of territory. This was one destabilizing possibility in the nuclear arms
race of the cold war. This can also lead to a discussion of the Carrington event where
in the 1800’s a monster solar flare cause telegraph outages and fires by induced
electric currents in some of the offices. Were such a flare to take place today there
would be blackouts on a continental scale and massive destruction of internet
infrastructure. That’s an interesting place to get to in a discussion that starts out with
some sparks in an office microwave!
Various Circuit Board Experiments
I have made a set of plexiglass circuit boards for my students. I use this in conjunction
with a collection of loose LED’s, resistors, photoresistors, capacitors, transistors, light
bulbs and motors to make basically any circuit I wish to make. These circuits can show,
by direct measurement by my own multimeters that students can use, various ideas in
electricity and how the components work. One of the most important principles to show,
by direct experience with the equipment and the circuit boards, is the loop rule: the sum
of differences in voltage around any closed circuit loop is always zero (you already
know a hiking version: the sum of elevation changes you experience in walking any
complete loop on a hike will always add to zero).