Download Lesson 25.2 Using Electromagnetism

Lesson 25.2 Using
Electromagnetism
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Printed: September 27, 2015
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C HAPTER
Chapter 1. Lesson 25.2 Using Electromagnetism
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Lesson 25.2 Using
Electromagnetism
Key Concept
A solenoid is a coil of wire with electric current flowing through it, giving the coil a magnetic field like that of a bar
magnet. An electromagnet is a solenoid wrapped around a bar of iron, which adds to the strength of the magnetic
field, making electromagnets the strongest of all magnets. Many common electric devices contain electromagnets.
For example, an electric motor is a device that uses an electromagnet to change electrical energy to kinetic energy.
Standards
• MCR.6-8.SCI.10.2
• AAAS.6-8.3.A.3; AAAS.6-8.4.G.3; AAAS.6-8.8.C.8; AAAS.6-8.12.D.4, 9
Lesson Objectives
• State how a solenoid increases electromagnetic force.
• Explain why electromagnets can be very strong.
• Describe how doorbells and electric motors use electromagnetism.
Lesson Vocabulary
• electric motor: device that uses an electromagnet to change electrical energy to kinetic energy
• electromagnet: magnet created by electric current flowing through a coil of wire that is wrapped around a bar
of iron or other ferromagnetic material
• solenoid: coil of wire with electric current flowing through it, giving it a magnetic field like a bar magnet
Teaching Strategies
Introducing the Lesson
Use the simple animated simulation at the URL below to introduce students to the magnetic field of a solenoid.
Point out how the compass needle points to the end of the wire coil, rather than toward the coil itself as it would if
a straight wire were used instead of a coil of wire. In other words, the coil of wire has a magnetic field like a bar
magnet, unlike the circular magnetic field of a straight wire. Tell students they will learn more about the magnetic
field around a current-carrying wire coil when they read this lesson.
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• http://micro.magnet.fsu.edu/electromag/java/compass/index.html
Demonstration
Demonstrate to the class how much stronger the magnetic field of an electromagnet is than the magnetic field of a
solenoid that is identical to the electromagnet except for the iron core in the electromagnet. You can make a simple
solenoid with a coil of wire and a battery and test the strength of its magnetic field by picking up paper clips with
it. Then you can turn the solenoid into an electromagnet by inserting a piece of iron, such as an iron nail, inside the
solenoid. Test the strength of the electromagnet’s magnetic field in the same way, by picking up paper clips. The
electromagnet should be able to pick up more paper clips than the solenoid.
Discussion
Discuss the benefits of using electromagnets, rather than permanent magnets, in devices that make use of magnetism.
A crane with an electromagnet for picking up very heavy metal items, such as the crane pictured in the chapter
opener, is a good example. Ask students how useful the crane would be for moving the metal items if it had a
permanent magnet, rather than an electromagnet.
Differentiated Instruction
To help students focus on the most important points in the lesson, provide them with a list of cloze prompts to
complete as they read. Sample cloze prompts for the first two headings in the lesson are given below (with sample
answers in brackets). Make sure students realize that each blank requires at least a few words to fill in correctly.
Sample cloze prompts:
1. A solenoid is a coil of wire with electric current flowing through it, giving it __________. [a magnetic field]
2. The magnetic field of a solenoid has __________. [north and south poles like a bar magnet]
3. The magnetic field of a solenoid is affected by factors such as __________. [amount and direction of current
and number of turns of wire]
4. An electromagnet is a solenoid wrapped around __________. [a bar of iron or other ferromagnetic material]
5. You can increase the strength of an electromagnet by __________. [adding more turns of wire in the coil,
increasing the current, or using a bigger iron bar]
Enrichment
Interested students can make a very simple DC motor by following the instructions at the URL below. You can
order a kit for the activity at the Web site, but the parts required are easy and inexpensive to obtain elsewhere. After
students build and test their motor, ask them to demonstrate it to the class and explain how it works.
• http://www.miniscience.com/projects/magnet_motor_kit/index.html
Science Inquiry
Have groups of students make a simple electromagnet by coiling a thin insulated wire around an iron nail and
connecting both ends of the wire to the terminals of a 12-volt battery. Ask students to use a bar magnet to determine
the polarity of their electromagnet and then try to reverse its polarity. (They should change the direction of the
current by reconnecting the ends of the wire to the opposite terminals.) They can see if they were successful by
using the bar magnet again to check the electromagnet’s polarity.
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Chapter 1. Lesson 25.2 Using Electromagnetism
Real-World Connection
Give students an opportunity to take apart a hair dryer or other small, commonly used electric device that contains
an electric motor. Help them identify the parts of the motor and what the motor does. You can learn more about the
motor inside a hair dryer at these URLs, which also include diagrams:
• http://home.howstuffworks.com/hair-dryer2.htm
• http://www.petervaldivia.com/technology/electricity/electrical-power.php
• http://home.howstuffworks.com/how-to-repair-small-appliances9.htm
Reinforce and Review
Lesson Worksheets
Copy and distribute the lesson worksheets in the CK-12 Physical Science for Middle School Workbook. Ask students
to complete the worksheets alone or in pairs to reinforce lesson content.
Lesson Review Questions
Have students answer the Review Questions listed at the end of the lesson in the FlexBook® student edition.
Lesson Quiz
Check students’ mastery of the lesson with Lesson 25.2 Quiz in CK-12 Physical Science for Middle School Quizzes
and Tests.
Points to Consider
In this lesson, you saw how electric current can be used to create a strong electromagnetic field. In the next lesson,
“Generating and Using Electricity,” you’ll find out how a magnetic field can be used to generate an electric current.
• Can you predict how this might be done?
• A device that uses a magnetic field to generate electricity is called a generator. What do you already know
about generators from previous chapters? (Hint: Look at the figure on how energy constantly changes form in
the “Introduction to Energy” chapter.)
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