Magnetism Module 27: Sources of Magnetic Fields Dynamic Study Module

Two points, point A and point B, are situated above a current-carrying wire. Point B is located at a distance R from the wire, which is twice as far from the wire as point A. By what factor is the magnetic field at point A larger or smaller than the magnetic field at point B?

2

A coil of wire is comprised of 5 turns, has a current of 2 mA running through it, and a net magnetic field at its center of B is equal to start fraction mu naught over 40 end fraction times T. What is the radius of the coil of wire?

20 cm

Individual electrons have a magnetic moment. In effect, they are very small magnets. In order for a ferromagnetic material to become magnetized, these electrons must do what with their magnetic moments?

Align their magnetic moments

Two long, parallel wires each carry the same current, I, and the two currents are parallel to each other. The two wires are a distance r apart. What is the magnitude of the magnetic field, B, at point P, the midpoint between the two wires?

B = 0 T, no direction because the fields cancel

The diagram below shows a long wire with a current of 2 A running through it that is going into the page. What would be the magnitude and direction of the associated magnetic field 4 cm away?

B = 25 times mu naught over pi, clockwise

Two long, parallel wires each carry the same current, I, but the two currents are anti-parallel. The two wires are a distance r apart. What is the magnitude and direction of the magnetic field, B, at a point that is at the midpoint, P, between the two wires?

B is equal to start fraction 2 times mu naught times I over pi times r end fraction, out of the page

The diagram below shows a long wire with a current of 5 A running through it that is coming out of the page. What would be the magnitude and direction of the associated magnetic field 5 cm away? Note that when calculating the direction, you will find that only one of the diagrams is correct.

B is equal to start fraction 50 times mu naught over pi end fraction, counter-clockwise

A solenoid has a net length of 2 m, a radius of 10 cm, and a current of 4 A running through it. The solenoid is comprised of 500 turns. What is the magnitude of the magnetic field in the solenoid?

1000 mu naught

Suppose you have a single bar magnet. If you cut that bar magnet into 10 equal pieces, how many individual magnets would you end up with? What will the polarity of each piece of magnet look like?

10 individual magnets, each with a north and south pole

A solenoid is comprised of 1,000 turns of wire and has a net current of 0.5 A running through it. Inside the solenoid is a magnetic field of 250 times mu naught. How long is the solenoid?

2m

You measure the magnetic field of a long, current-carrying wire to be B is equal to start fraction mu naught over 50 times pi end fraction at a distance of r = 7.5 cm. How much current is running through the wire?

3mA

Which of the following ways can you use to make a permanent magnet? (Choose one.)

Apply a magnetic field to something ferromagnetic

At the atomic level, what must happen in order for a ferromagnetic material to become magnetized?

Individual atomic magnetic moments need to align.

In the diagram, a conducting loop has a current running through it counter-clockwise. In which direction is the magnetic field outside of the loop going to be pointing?

Into the page

Taking note of the direction of the flow of current in the solenoid, in what direction does the solenoid's magnetic field point?

To the left

How will the field strength in the solenoid be affected, if the number of loops in a solenoid is decreased by a factor of 4?

The field strength will be decreased by a factor of 4.

How will the magnetic field strength found inside of a solenoid be changed if the length of the solenoid is decreased by a factor of 5?

The field strength will be increased by a factor of 5.

How will the magnetic field inside of a coil of wire be changed if the radius of the coil is decreased by a factor of 10?

The magnetic field strength will increase by a factor of 10.

The diagram below is a close-up view of a material, showing the atomic magnetic moments associated with the atoms that make up the material. Based on the relative orientations of these atomic magnetic moments, what can you say about the material?

The material is magnetized (If arrows are pointing in the same direction) The material is NOT magnetized (if the arrows are basically pointing every direction)

Within a ferromagnetic material, there are small regions called magnetic domains. What is responsible for the creation of these magnetic domains?

Unpaired electrons, each with a net magnetic moment, aligning

The diagram below shows a close-up view of a material's magnetic domains. A small magnet is brought near the material, but only some of the domains have aligned with the permanent magnet's field. Is this a reasonable result?

Yes, because a very strong magnetic field is required to align all of the magnetic domains.

In the diagram, a conducting loop has a current running through it clockwise. In which direction is the magnetic field inside the loop going to be pointing?

into the page

A coil of wire is made of 10 turns, has a radius of 4 cm, and a length of 2 mm. If the current running through this coil is 2 mA, what will be the magnitude of the magnetic field?

mu naught over 4 - B= u0NI / 2R B= u0(10 turns)(2mA)/2(0.04)