Exploratorium Field Trip Pathways


Teacher Version
Electricity, Motors, and Meters

The following California State Science Standards are relevant to this Pathway:

Grade Topic Subsection
9–12 Physics 5. e, f, g, h, j

California State Standards

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.


Can't find an exhibit or have a question? Ask an Explainer.

Circles of Magnetism I

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, north.

 

 

What happens to the compasses as you get further from the wire?

 

 

 

 

Motor Effect

Try to push the wire down.

  1. From which direction does it feel like there's a force acting on the wire?
    Right side.

  2. 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)

 

 

 

Daisy Dyno
Related Material:
Exhibit Information

 

  1. 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).

  2. Try to find the path of the electric current, and make a simple diagram of this path.


  3. What similarities can you find between this exhibit and Motor Effect? They both have a magnet, electric current, and a force (something moves).

  4. Is there another place on the disk where it will spin well?
    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.

  5. 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.

 

 

Stripped-Down Motor
  1. 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.


  2. 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).

 

 

Giant Meter

 

 

 

 

Magnetic Suction

 

 

  1. 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.

  2. 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.

 

 

Generator Effect

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.