Teacher: Mr. James

Grade: 91

Topic: Electricity and Magnetism Lesson 4

Date May 19, 2020

Duration: 1 weeks

Objectives

Students will:

1. Perform simple activities to identify the poles of a bar magnet

2. Demonstrate that unlike poles attract and like poles repel

3. Construct an electromagnet

Video Links: 1. https://youtu.be/MZtTVsIOA9c 2. https://youtu.be/BbmocfETTFo

Magnetic Fields

Magnetic field lines spread out from one pole, curve around the magnet, and return to the other pole.

When the magnetic fields of two or more magnets overlap, the result is a combined field.

Magnetic Domains

In a magnetized material, all or most of the magnet domains are arranged in the same direction.

Modern magnets come in a variety of shapes and are made from many different materials.

Making and Changing Magnets

Each piece of a magnet retains its magnetic properties after it is cut in half.

Earth as a Magnet

Just like a bar magnet, Earth has a magnetic field surrounding it and two magnetic poles.

Movement of Earth’s Magnetic Poles

Earth’s magnetic poles move slowly over time. The data in the table show the position of Earth’s magnetic north pole in specific years.

The Magnetosphere

The solar wind causes Earth’s magnetic field to stretch out on the side of Earth not facing the sun.

Electric Current and Magnetism

An electric current produces a magnetic field.

Solenoids

The magnetic field produced by a current has three distinct characteristics. The field can be turned on or off, have its direction reversed, or have its strength changed.

A solenoid is a type of electromagnet when the purpose is to generate a controlled magnetic field.

The magnetic field around a solenoid resembles that of a bar magnet.

Electromagnets

A doorbell rings as the magnetic field of an electromagnet turns on and off.

Electromagnets are used to lift heavy objects. A switch is turned on in the crane so that a current is produced in the electromagnet.

Activity

1. What is the minimum number of poles for a magnet? _______________________

2. When you break a magnet in half, how many poles does each piece have? ________________

3. The north pole of a magnet is attracted to the geographic North Pole of Earth, yet like poles

repel. Can you explain this? ____________________________________________________

4. Which way would a compass needle point if you were at the magnetic north pole?

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5. What is a magnetic domain? ___________________________________________________

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6. Why are iron atoms so strongly affected by magnetic fields? _________________________

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7. When a magnetized steel needle is strongly heated in a Bunsen burner flame, it becomes

demagnetized. Explain why. ___________________________________________________

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8. If an unmagnetized piece of iron is attracted to one pole of a magnet, will it be repelled by the

opposite pole? _____________________

9. In the figure below, two permanent magnets with holes bored through their centers are placed one over the other. Because the poles of the upper magnet are the reverse of those of the lower, the upper magnet levitates above the lower magnet. If the upper magnet were displaced slightly, either up or down, what would be the resulting motion? Explain. What would happen if the upper magnet were inverted?

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10. A conductor carrying a current is arranged so that electrons flow in one segment from east to west. If a compass is held over this segment of the wire, in what direction is the needle deflected? (Hint: Recall that current is defined as the motion of positive charges.)

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