Download IB Physics SL Y2 @ RIS – Unit 13, Magnetism: Faraday`s Lab

AP Physics B @ SCHS – Unit 10, Magnetism: PhET Faraday’s Lab
Name:
Date:
background:
Remember the paradigm for this unit: a current-carrying wire has a magnetic field around it. A permanent magnet also has a magnetic field
around it, even though no current flows through it. Clearly, a net current is not necessary for a magnetic field. What is going on? It looks
like we need moving charge to create a magnetic field, but charge is in motion in all materials, magnetic or not. It turns out that some
materials are permanently magnetic because the arrangement of the molecules in them orients the electron motion so that the motion isn’t
completely random. If the arrangement of the material results in random electron motions, the magnetic fields of all of the moving
electrons cancel out. The more strongly the electron motions of the molecules are oriented in the same direction, the more strongly
magnetic a material will be.
Magnets are said to have two poles: “North” and “South.” Much like the terminology for electric charge (positive and negative), the names
don’t mean what they mean in non-scientific terms. They symbolize that the two poles behave oppositely to each other. The north pole of
a magnet is attracted to the North Pole of the earth, and vice versa. By definition, magnetic field lines begin on north poles and end on
south poles.
If moving charge can make a magnetic field, can a moving magnet make charge move? This is one of the questions you will investigate in
this activity.
instructions:
Go to
http://www.colorado.edu/physics/phet/simulations/faraday/faraday.jnlp and start the simulation.
Bar Magnet
Select the tab marked “Bar Magnet.” Behind the bar magnet you will see a black field with many compass needles on it, and a compass.
You can drag the bar magnet and the compass around, but the compass needles are fixed on their axes. Move the magnet and the compass
around.
1. How does a compass needle work? Hint: Where are the “North” and “South” pole of the compass needle?
2. Sketch complete field
lines (not the compass needles
the simulation shows!) for an
idealized bar magnet like the
one you see in the simulation.
Check the box labeled “See
inside magnet” to see the
direction the compass needles
point inside the magnet.
N
S
3. Now select “Show Field Meter.” How does the field change as you move the meter farther away from the magnet? How does your
field sketch represent this?
Pickup Coil
Select the tab marked “Pickup Coil.” When the light bulb lights up it indicates that a Voltage is making an electric current flow. You may
also change the light bulb to a voltage meter. Move the magnet around and observe what happens to the strength of the magnetic field
inside the coil of wire and to the light emitted by the bulb. This process is called electrical generation or induction.
4. Describe the ways that moving the magnet generates the largest PD (Voltage). Move the magnet back and forth, fast and then slowly.
What general rules can you deduce about the motion of the magnet and induced current? Hint: Use the field strength meter. Does
constant field strength in the coil induce a current?
5. Leave the magnet in one place and using the button on the right control panel of the applet, flip the polarity of the magnet. Flip the
polarity of the magnet slowly and then quickly. Observe the amount of light emitted by the bulb. What general rules can you deduce
about changing the polarity of the magnet and the induced current?
6. Leave the magnet in just one place and using the slide on the right control panel of the applet, change the strength of the magnet.
Change the strength slowly and then quickly. Observe the amount of electricity that is generated. What general rule can you deduce about
changing the strength of the magnet and the induced Voltage?
7. Change the number of loops and then generate electricity by changing the magnetic field. What general rule can you deduce about the
number of loops in the pickup coil and the induced Voltage?
8. Change the area of the loop and then generate electricity by changing the magnetic field. What general rule can you deduce about the
area of the loop in the pickup coil and electrical generation?
9. Why do you think it is called a pickup coil? Hint: What does it pick up?
10. Qualitatively describe the energy changes that occur if you were to induce an electric current by moving a magnet near a pickup coil.
Where does the energy start out? Where does it end up? How does it get there?
Generator
11. To make a generator, you would use the principles you discovered in playing with the pickup coil. Suppose you are to design a
generator that produces the maximum amount of electricity possible. Make a list of the characteristics it would have.
12. Click on the “Generator” tab and test your list above. How does the simulation accomplish what you listed above? Does it include
anything additional?