Electric Charges
What to do:
Blow up a balloon and rub it against your hair. Does your hair stand up when you
take away the balloon? If you bring the balloon close to your hair, is your hair
attracted to the balloon?
2) Lay an empty soda can on its side on a
flat table. Hold a charged balloon close
to it. What happens?
How it works:
3) Turn on the kitchen faucet so a small
stream of water comes out. Hold a
charged rod or balloon up close to the
water stream. What happens? Do you
think different liquids will react the same
way to the charged object?
Rubbing causes electrons to transfer between objects. The balloon picks
up electrons from your hair and becomes negatively charged. Your hair
becomes positively charged. Since like charges repel each other, your hair
sticks out (all the positively charged hairs are pushing each other away).
Opposite charges attract, so your hair is attracted to the balloon. Next
time your family does laundry help take the clothes out of the dryer. Do
any of the clothes stick together? Can you explain why?
Induced Electric Charge
What to do:
Charge a balloon by rubbing it against your hair or a piece of wool. Press
the balloon against a wall or other vertical surface and let go. What
happens? Try it with a conducting surface (metal) and non-conducting
surface (wall). In insulating materials the electrons cannot move. In
electrical conductors the electrons are free to move around. Try it with
different color balloons. Are there any differences?
How it works:
The negative charge on the balloon causes the
electrons in the wall to shift slightly away from the
surface (for both conducting and non-conducting
surfaces). Even though the wall is still neutral
(same number of positive and negative charges) the
surface is slightly positive. This is called an induced
charge. Sometimes the different chemicals used in
coloring the balloons changes the balloon’s ability to
pick up charge.
More Induced Electric Charge
What to do:
1) Cut pieces of paper into ¼ inch squares and leave them on a table. Charge
a balloon by rubbing it against your hair or a piece of wool. Bring the balloon
close to the pieces of paper. What happens at first? Are the paper pieces
attracted to the balloon? What happens later? Do the paper pieces stay
stuck to the balloon?
4) Blow some soap bubbles. Bring a charged balloon close to the bubbles.
Is it attracted to the balloon? Can you get the bubble to stay suspended in
the air? Do you hold the balloon above or below the soap bubble?
5) Blow up two balloons and hang them from
separate strings (from the edge of a table or in a
doorway) so that they are close together. Charge
the balloons by rubbing them with a wool cloth or
with your hair. What happens to the balloons?
Now, hold a piece of paper between the balloons.
What happens?
How it works:
The charge on the balloon causes the electrons
in the other objects to shift slightly away from
the surface of the object (it doesn’t matter if
it is a conductor or insulator). Even though the
objects are still neutral (same number of positive and negative charges) the
shifting of the electrons causes the surface to be slightly positive and it
is attracted to the negative balloon (closeness counts in electricity). This
is called an induced charge. If
the objects touch, electrons can
transfer and the two objects will
have the same charge and repel.
Some molecules, like water, are
polarized. That is, one side
is slightly negative and the
other slightly positive. The
water molecules rotate so that
the positive side is closer to
the negative balloon and it is
attracted to the balloon. I’ll say it again,
closeness counts in electricity!
Magnetically Induced Current
What to do:
Drop a strong magnet down a copper pipe. Time how long it takes to go
down. Now drop something that isn’t magnetic. Which takes longer?
How it works: The falling magnet makes a changing magnetic field in
the pipe. A changing magnetic field causes a current to flow in the pipe.
Currents create magnetic fields. The current created in the pipe causes
a magnetic field that opposes the falling magnet and makes it drop at a
slower rate.
Electricity and Magnetism
Home Experiment Guide
The
Energy and the Environment
All the electric devices in our homes use energy. The electric energy
comes from power plants that get energy from other sources and change
it into electrical energy. The energy comes from burning oil, burning coal,
the motion of water, or nuclear reactions. All of these sources of energy
have negative side effects. A negative side effect is something bad that
happens when we are changing the energy into electrical energy. An
example is air pollution that is released when coal burns. So, it is very
important that we all do our part to use less energy.
If you can‛t have fun with physics...
...you aren‛t a very fun person
What to do:
Replace an old lightbulb (incandescent bulb) with a new compact fluorescent
lightbulb (CFL). Hold your hand close to an incandescent bulb after it has
been on for a while (don’t touch it!). Now, do the same with a CFL bulb.
Which bulb is wasting more energy by giving off heat instead of light?
How it works:
Incandescent bulbs are not as efficient at changing electrical energy into
usable light as CFL bulbs. In a typical incandescent bulb only 2% on the
energy we put in gets changed into light we can use. ACFL bulb changes
about 8% of the energy we put in into light we use.
Contact Info:
Frank Cascarano, Physics Instructor
cascaranofrank@foothill.edu • 650.949.7784
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Please visit our website or Facebook page for a “Home Experiment Guide”
www.foothill.edu/physics
Physics Department logo and guide layout by ASFC Design Center
Don’t try this at home ... we’re professionals!
But there are lots of things you can try at home.
For a few suggestions, look inside the pages of this pamphlet.