Electricity - Induction

HS-PS2.5 Plan and conduct an investigation to provide evidence that an electric current can produce a magnetic field and that a changing magnetic field can produce an electric current. 

Engage

• • Experiment with hand-held generators, motors, fans and light bulbs (see movie)

  • Record as many observations as possible in the quickwrite.

Explore

• Explore with tangible items

  • • Download a worksheet to collect data

    • Connect two hand-held generators to each other using the connecting wires and alligator clips. Change independent variables and observe changes in dependent variables and record your findings.

      • Independent variables

        • direction of generator 1

        • speed of generator 1

      • Dependent variable

        • Response generator 2

    • Download a free EMF meter (e.g. Tesla Meter) to your cell phone

      • Investigate and record the EMF field around generator 1 & 2 under a variety of conditions

• • Explore with simulations. Open the Faraday's Law simulation. 

    • Questions

      1. Investigate and record the magnitude of the induced voltage. 

      2. What happens as you move the north side of the magnet into the coil?

• • 1. How does the voltage change as you move the south side in rather than the north?

    2. What happens if you move the magnet into the coil very slowly vs. very quickly?

    3. What relationship can you make between the motion of the magnet and the current produced?

    4. What relationship can you make between the number of loops and the current produced?

    5. Put the magnet in the loops and click the magnet flip button.  What happens as you spin the magnet several times?

    6. Look at the Voltage needle as you spin it multiple times.  What type of  current do you think it is producing?  AC or DC?

• • • Challenges

      • How many ways can you cause induction? 

      • Explain your method(s) citing evidence from the simulation.  

      • Sketch two different situations in which the light bulb lights up. Indicate the N/S poles of the magnet and the direction of its motion. 

      • What is the direction of the induced current in each case? 

      • Predict what happens to the brightness of the bulb when the number of turns in the coil is reduced by half, but the speed of the magnet remains the same. 

      • How does the speed of the magnet affect the brightness of the bulb? 

Explain

• • Faraday's law of induction is a basic law of electromagnetism predicting how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF)—a phenomenon called electromagnetic induction. It is the fundamental operating principle of transformers, inductors, and many types of electrical motors, generators and solenoids.

  • Faraday's law states that the EMF is also given by the rate of change of the magnetic flux: where is the electromotive force (EMF) and ΦB is the magnetic flux. The direction of the electromotive force is given by Lenz's law. Faraday's law states that the EMF is also given by the rate of change of the magnetic flux: