When you bring an electric current
and a magnet together, interesting things can happen. At each exhibit
on this Pathway, try to find the permanent magnets, the path of the
electric currents, and the forces created by them.
Describe the pattern the innermost circle of compass
needles makes when the current is running and when it is not.
When the electricity is on, the needles point
in a circle around the wire with the red ends pointing clockwise. When
the electricity is off, all the red needles point in the same direction,
What happens to the compasses as you get further
from the wire?
Try to push the wire down.
- From which direction does it feel like there's
a force acting on the wire?
- What can you see here that might be creating a
force on the wire?
Magnets an an electric current (althought electricity
can't be seen)
- Touch the tip of the wire to the metal disk in
various places. Where is the wire touching the disk when the disk
spins? Underneath the magnet (any place where
it sets up a current that runs between the two poles of the magnet).
- Try to find the path of the electric current,
and make a simple diagram of this path.
- What similarities can you find between this exhibit
and Motor Effect? They both have a magnet, electric
current, and a force (something moves).
- Is there another place on the disk where it will
No. A deeper explanation: When you hold the
wire so that the electrons flow beneath the permanent magnet, the
magnetic field pushes against the moving electrons, making the disk
spin. The closer you move to the center, the less the disk spins because
the electricity has a shorter path to the center. When you touch a
part of the disk that is not under the magnet, the magnetic field
created is not generally close enough to the magnet to create the
spin. (Within about 2 inches, there is enough attraction to make the
disk spin slowly.) The underside of the disk has a plastic coating
that serves as an insulator so no magnetic field is created.
- What is the relationship between how the disk
moves and how the wire moves in the previous exhibit?
Answers may vary. In these two exhibits, the
flow of electricity creates a magnetic field, which is repelled by
the magnetic field of the magnets.
- Start with the power source and follow the wires
to see how the electricity travels through this motor. Sketch the
path of the electricity in the box below.
- If you could, how could you reverse the direction
of this motor's spin?
You could reverse it if you reversed the flow
of electricity or if you flipped the magnets (magnetic field).
- When the light goes off, is there any magnetic
force between the rod and the coil on the left? Why?
No. When the light goes off, there is no electricity
running through the circuit, so there is no magnetic force.
- How are the doorbell and the pinball flipper
like the rod and coil?
Answers may vary. Both of these objects have
a rod and coil. When the magnetic field of the coil pulls the rod
of the doorbell back, it hits a metal plate making a "ding."
When the electricity flow is stopped, the rod is released from the
magnetic field of the coil and hits another plate making the "dong."
In the pinball lever, the magnetic field of the coil pulls the rod
back, pushing the flipper up.
How does the brightness of the light change if you
pull the handle slowly or quickly?
The faster you pull it, the brighter the light.
When the wire moves faster, a greater voltage is created, and as a result,
a greater current moves through the circuit.