AP Physics B Magnetism: Conceptual Webquest

Magnets are created by moving charges. ~In a stationary (bar) magnet, the spinning electrons in iron create the magnetic field. ~In a wire, electrons are flowing through the wire as current. ~In a third case, charged particles can be moving on their own. ~In this webquest, we will look at all three situations and the resulting magnetic fields and forces.

Intro:  Basics of magnetic fields

• What causes a magnetic field?
• What is the symbol used to represent magnetic fields?

3. What units are magnetic fields measured in?

4. Magnetic fields exert forces on other magnets and on moving charges (because moving charges ARE magnets)

5. Write the equation for the force a moving charge will feel as it moves through a magnetic field.

6. Will a magnetic field exert a force on a stationary charge?  Use the equation from question 4 to explain why or why not.

Part I: ~Stationary (bar) magnets

Click on the link above and look at the magnetic field lines produced by a bar magnet

Note the direction of the magnetic field lines. ~Do they point toward or away from the North magnetic pole?

Do the magnetic field lines point toward or away from south magnetic pole?

Part II: ~Magnetic field around current-carrying wires

Click on the link above.  Notice that the arrow indicating the direction of current is OPPOSITE the direction the electrons are flowing. ~For some reason that nobody really understands, we define current as a flow of positive charges, which is opposite the direction of the flow of electrons. ~Weird, but true.  Sketch the direction of the magnetic field produced by this wire.  (Use an x to represent a field going into your paper and an o to represent a field coming out of the paper.)

Click on the link above.  Scroll down to right-hand rule #2.  Explain the right-hand rule for determining a magnetic field around a wire. ~Label the diagram on your worksheet. ~What value does your thumb represent?  What value do your fingers represent?

Draw the electric field around the following wires (shown on your paper).  Remember that an x is an arrow pointing into the page and an o is an arrow pointing out of the page.

As we know, magnets can either repel or attract one another.  Which means that so can current-carrying wires (since they are magnets!).

Watch the video below.

When the wires are connected in parallel (switch pulled backward, the circuit is shown below.  The magnetic fields around the wire are as shown on your paper:

Do the wires attract or repel when they are connected in parallel?  Try to explain why, using the magnetic fields above.  (Hint:  do north poles attract other north poles, or do they attract south poles?)

When the wires are connected in parallel (switch pulled backward, the circuit is shown on your paper.  Sketch the magnetic field around the two vertical wires:

Do the wires attract or repel when they are connected in series?  Try to explain why.  (Just do your best – this is a difficult question)

Part III: ~Charges moving through magnetic fields

Describe the right-hand rule for charges moving through magnetic fields.  What does your thumb represent?  What does your pointer finger represent?  What does your middle finger represent?

Is the right-hand rule used for positive or negative charges?

What path does a charged particle take when it is moving through a magnetic field?

Click on the above link and watch the animation. Using your Right-hand rule, predict the direction of the force on a particle traveling through the magnetic field shown (the field is into the page).  Is this the same direction as the force shown?  If not, why not?

• For each of the following situations, draw the direction of the magnetic force acting on the moving charged particle.  The velocity is shown on your sheet.

X       x       x       x               o       o       o       o

X       x       x       x               o       o       o       o

X       x       x       x               o       o       o       o

X       x       x       x               o       o       o       o

X       x       x       x               o       o       o       o

X       x       x       x               o       o       o       o

X       x       x       x               o       o       o       o

X       x       x       x               o       o       o       o

X       x       x       x               o       o       o       o

X       x       x       x               o       o       o       o