Unit 4 Lesson 2: Electromagnets & Inducing Currents

Where does the magnetism of a permanent magnet come from? P.263

the motion of electrons in aligned atoms that reinforces the magnetic field of each electromagnet

Which of these describes how a magnet picks up paper clips? P. 263

The ferromagnetic material in the paper clips realigns under the influence of the magnet’s magnetic field so that each paper clip becomes a new magnet.

Which of these can be used to induce a current in a closed circuit without the use of a battery or an electrical power supply? P. 264-266

a magnetic field

What is electromagnetic induction? P. 268-269

formation of a voltage across a conductor in a changing magnetic field

Hydroelectric power plants produce electricity. Which form of input energy does the plant transform to generate the electricity? P. 265

kinetic energy

Which alignment is expected of the lines of the magnetic field around a current-carrying wire? P. 264-265 & 268

concentric circles around the wire

Which of these describes the process of magnetic resonance imaging (MRI)? P. 275

Hydrogen atoms align with the magnetic field and emit radio waves once the field is shut off.

Many technologies use changing magnetic fields. What happens if a changing magnetic field is placed near a wire? P.268-269

The formation of an electric field generates an electrical current in the wire.

A long piece of copper wire is coiled into the shape of a spring. Which event occurs when a long bar magnet is moved back and forth repeatedly within the coil even though the magnet does not touch the coil?

The moving magnet generates a magnetic field that causes an electric current in the wire.

A student brings a horseshoe magnet close to a pile of iron shavings. Two piles of shavings attach to each pole of the magnet. Explain why the iron shavings are gathered at the poles of the magnet. P. 264

Iron is a ferromagnetic material. In the presence of a magnet, the atoms align with the magnetic field and become their own magnets. Once magnetized, the opposite poles of iron shavings are attracted to the larger magnet's pole.

Two students design a basic direct current, or DC, motor for a mini-train they are designing. They mount a loop of wire horizontally between two unconnected magnets, one with the north end facing the south end of the other magnet. They attach a ring at one end of the wire loop. They attach the ring to a battery, which allows the flow of DC current to move through the wire loop. P. 270-274 a) Describe what will happen to the loop of wire once electric current is flowing through it. b) Explain why this happens to the loop of wire attached to the ring and battery.

a. Once there is an electric current through the loop, it will begin to rotate.

b. The movement of the electric current in the wire loop creates a magnetic field. At one instant the field will be of the same polarity as one fixed magnetic poll, thus repelling the wire making the loop rotate to the next fixed poll where it’s attracted. There will be a continual attraction repulsion between the wire magnetic poll and fixed magnetic polls.

Explain how the strength of a magnetic field generated by a current-carrying wire changes when it is moved from 5 cm to 10 cm away from the wire. P. 263

Moving a point from 5 cm to 10 cm away from a wire carrying a current decreases the strength of the magnetic field by a factor of four. This is because the strength of the magnetic field is inversely proportional to the square of the distance from the wire.

Mercury is a solid planet with a molten iron core. Explain why you may or may not expect Mercury to have a magnetic field. P. 266-268

It may be expected of Mercury to have a magnetic field similar to earth. Within the earth, molten iron in the outer core generates a current due to convection, and a movement of the conductive material produces a magnetic field. The same should occur with Mercury.

A student wraps a cylindrical piece of nickel in 10 rounds of wire and runs a 5.5-amp current through the magnet to make an electromagnet. Explain how the strength of the magnetic field would change if the student wrapped the wire 5 extra rounds and increased the current to 10 amps. P. 262-263

If the student wraps the wire 5 extra rounds and increases the current to 10 amps, the strength of the magnetic field will increase. The magnetic field strength is directly proportional to the number of wire rounds and the magnitude of the current. Therefore, the strength of the magnetic field will increase by a factor of 3/2 due to the increase in the number of wire rounds and the current.