Download Red tip points toward the bar magnet`s `south`

Faraday’s Electromagnetic Lab
On the phet.colorado.edu website, use the ‘Faraday’s Electromagnetic Lab” simulation.
Bar Magnet Tab: properties of magnetic fields
1. You should see a bar magnet and compass. Red is magnetic North and white refers to
magnetic South. Place the compass at the North end of the magnet and observe which
way the ‘red tip’ of compass points. Move the compass to the South end and observe
where the ‘red tip’ points. Adjust your notes/diagram from class according to your
observations.
2. What does the red tip of the compass point toward?
Red tip points toward the bar magnet’s ‘south’ and away from the bar
magnet’s ‘north.
3. The Big Idea: Use your answer to #2 to explain why the earth’s “North Pole” is actually
the magnetic south pole.
Compass is designed to work by pointing us toward ‘north’. But it is
actually attracted to magnetic south.
Electromagnet Tab: Factors that affect magnetic fields around current carrying wire
4. Keep the setting on DC. How is the magnetic field you see similar to Faraday’s
experiment ? How is it different?
Similar because it shows mag field around a current carrying wire;
different because the straight wire is bent into a coil and this has changed
the shape of the mag field
5. Draw a picture of the loop of wire, the direction of the flow of electrons and the
direction of the magnetic field.
6. What happens to the field when you:
a. decrease and increase the battery voltage?
Mag field weakens and strengthens; also current slows and
quickens
b. Reverse the voltage?
Current reverses and Direction of mag field inside and outside the
coil reverses
c. Decrease and increase the number of loops?
Fewer loops means weaker mag field; current is still the same level
7. Change the setting to AC.
a. What was the battery replaced with?
A box labeled AC current supply that shows current going up and
down over time (sine wave?)
b. What happens to the current?
On the graph, The current increases to positive and then passes
through zero and increases again to a negative value; in the loop, it
goes back and forth instead of only one direction like DC.
c. What happens to the field?
The mag field is constantly flipping direction, e.g. reversing polarity. It
stays the same strength in the center of the coil, just flips direction.
8. Observe the motion of the electrons in AC and compare it to the motion in DC. Explain
the difference between AC and DC in terms of electron motion.
In DC electrons move smoothly in one direction only. In AC the electrons move
back and forth in a cyclic rhythm. In DC the current and voltage maintain
steady level values. IN AC the current and voltage flip between high positive
and high negative in a cyclic way.
9. The Big Idea: Flow of electrons or current in a wire creates a magnetic field around
the wire. A wire carrying DC current has a steady mag field . A wire
carrying AC current has a mag field that reverses polarity (flips direction )
in a cyclic way.
10. Based on your answers, what are the factors that affect the strength of a magnetic field
around a current carrying wire?
Level of current, number of loops of coils, the shape of the wire (straight
vs coil)
Pickup coil Tab: combining the magnet and a closed circuit containing a lightbulb
11. Set the number of loops to 1. What happens to the lightbulb when
a. The magnet is not moving and is not in the loop?
Nothing, bulb is dark
b. The magnet is moving but is not in the loop?
Bulb lits up a little, flickers, very little current in loop
c. The magnet is not moving but is in the loop?
Nothing, bulb is dark
d. The magnet is moving and is in the loop?
Bulb lights up a lot more, still flickers, more current in loop
12. How does the speed of the magnet affect your results in 10 b and 10 d?
faster motion of the magnet increases the bulb’s brightness.
13. What type of current is created in the loop: DC or AC?
a. How do you know which kind it is?
AC because the electrons go back in forth in the wire instead of one
direction smoothly
14. The Big Idea:
a. A _moving_ magnet can be used to induce/create_ a/an
alternating_current in a closed circuit.
b. Even better: a changing magnetic field can be used to induce/create a/
alternating_ current in a closed circuit.
Transformer Tab: Putting it Together
15. Keep the setting on DC. In order to create a current in the closed loop on the right,
what must you do with the loop on the left?
Can increase and decrease the voltage repeatedly OR reverse the voltage
so the current flips direction, OR move the entire battery/coil assembly
16. Do that (answer to #15).
a. How do the electrons move in the loop on the right?
The electrons move back and forth repeatedly.
b. Describe how the bulb reacts.
The bulb lights up and flickers
c. What type of current in being created in the loop on the right? DC or AC?
i. How do you know?
AC because the motion of the electrons is back and forth not
smooth in one directioin like DC.
17. What happens if you move the loop on the right?
a. Answer a-c again.
the bulb lights dimly and flickers, the current in its own coil is AC again.
18. Change the setting to AC.
a. Do you have to do anything for a current to flow in the loop on the right? No
extra work is required, no relative motion, etc.
i. Describe the magnetic field around the loop on the left.
The mag field is now flipping direction in a cyclic way.
ii. What is causing the current in the loop on the right?
The changing mag field is inducing/creating a current in the second,
separate coil.
19. The Big Idea: The changing magnetic field around a circuit carrying alternating
current can be used to create an alternating current in a separate loop.
YAY TESLA!!!!
Generator Tab: Describe the transformation of energy from the beginning to the end!
The falling water has kinetic energy and momentum. The water collides with
the wheel and exerts a force on the paddles and makes the whole thing rotate.
The bar magnet is attached and it rotates also. When the mag field changes
direction over and over again, it induces/creates a voltage and current in the
closed loop of coil and light bulb. The potential and then kinetic energy of the
water is transformed to the rotational KE of the wheel and magnet. The
changing mag field induces a voltage and current, therefore power or electrical
energy over time.