Electromagnets

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Objective

SWBAT make an electromagnet and evaluate how turns of the wire change the strength of the electromagnet

Big Idea

What - we can make out own magnets?

The Need for the Lesson

Students are curious about electricity. It is both mysterious and dangerous. Magnets are common objects students encounter everyday.

This lesson connects prior student knowledge of magnets to electricity. Electromagnets help prepare students to connect their understanding of the Earth's magnetosphere in Earth Science. Students will then be able to make connections to see the Earth as an electromagnet with the source of the current in the movement of the core. 

Students make a connection between electricity and magnetism. They develop their understanding of cause and effect relationships.

Investigation Preparation & Summary

10 minutes

Students will create and evaluate the changes in the strength of the electromagnet when the number of turns of the wire is changed (MS-PS2-3 Ask questions about data to determine the factors that affect the strength of electric and magnetic forces.).

Students take quantitative measurements by counting the number of paperclips held and measuring the strength of the electromagnet using a spring scale (SP3 Planning and Carrying Out Investigations).

Student will attend to precision in their data collection (MP6 Attend to Precision) especially when reading the spring scale. The collected data will be graphed first comparing the number of winds to the number of paperclips held, then comparing the number of winds to the the strength of the electromagnet as measured by the spring scale (SP5 Using Mathematics and Computational Thinking by creating a graph to visually identify patterns) (MP2 Reason Abstractly and Quantitatively).

Students will write conclusions stating the relationship between the increasing number of winds to the number of paperclips held and the measured strength in grams using the spring scale. (SP4 Analyzing and Interpreting Data, SP6 Constructing Explanations and Designing Solutions, SP7 Engaging in Argument from Evidence)

To prepare for this lesson, each student group will need a meter of plastic coated wire with both ends stripped. I do this ahead of time to avoid delays while students are waiting for a wire stripper. A complete materials list is in the resources section.

Students in Action

45 minutes

Electromagnets

Can we make a magnet? "Well, it looks like we can," is the response from one of my students. What makes you say so? "We are going to be counting the number of paperclips lifted so we must be making a magnet." I love, love, love this answer. This means that the students have read the question and skimmed through the lesson without my prompting. They are curious and we are ready to go!

Before we start the lesson, we quickly review circuits. In the previous lesson, Circuits: A Probe for Prior Knowledge Becomes a Lesson, I discovered that none of my students could make a circuit to light a bulb using only a wire, a bulb and a battery. We examine the drawing on the Electromagnet student sheet and note that the circuit will be a wire wrapped around a nail or bolt with one end of the wire connected to the positive side of the battery and the other end of the wire connected to the negative side of the battery.

We also take a look at how the wire is wrapped around the nail or bolt and see that the wraps are neat and do not overlap. I share with students that we do not want to make how the wire is wrapped around the nail or bolt a variable in our experiment, so we will neatly wrap the wire in one direction with no overlap of the wire. The nails and bolts selected are long enough to accommodate the maximum 50 winds required in the lesson.

I walk around as students are collecting their data. At first students are only trying to pick up paperclips using either end of the nail or bolt. I see a group collecting paperclips all along the length of their nail. I ask the class to pause their own investigations to observe this group. Students are delighted with the increase in paperclips their electromagnet is holding and they observe that the magnetic field is not limited to the poles but indeed exists along the nail or bolt.

Some students experience problems with the spring scale. They should be adding a washer to the end of the spring scale and allow the electromagnet to pull on the washer recording the number of grams read. We are not accounting for the number of grams of the washer for this test. The number is not significant enough to influence the overall trend of the data.

Student graph creation is also something I am monitoring as students finish their data collection. I want their observations to be accurate so I am checking that their graphs. Students are not yet proficient in creating and analyzing graphs in science class. (SP4 Analyzing and Interpreting Data

      • Give your graph a title
      • Label the axis, include units
      • Use intervals that are equally spaced    

             

As I look at the graphs, I ask students why they think we are taking the data from the table and creating a graph. The most common answer is because it is easier to answer questions about the data. They appreciate the power of visuals.

Does Diameter Matter?

As students complete this lesson, a few students ask if the diameter of the core, a nail or bolt, matters in determining how strong the electromagnet will be. Great question! Students add a data table and we swap out their nail for a bolt or bolt for a nail to test.

Our results were not conclusive. As a class we generated many more I wonders than we had time to find answers. 

One student expressed concern that the change in diameter was not significant enough to verify cause and effect. Other students wondered if the increase of diameter just caused more wire to be used. We already know that the increase in winds increases strength of the electromagnet. Additionally we wondered if the composition of both cores was identical.

This is a great lesson when students continue to ask questions!

While we were unable to continue exploring the electromagnet due to time constraints, a couple of students expressed interest in exploring electromagnets further for their science fair projects.

 

This video walks through the student sample lesson. I was surprised by the errors I found not on the student data collection but on the student graphs. I will be spending some time with our lead math teacher to develop a graphing mini lesson for my students next time we create graphs in class!

Connecting the Learning

20 minutes

One of the things I noticed is that my students did not mention the ability of the electromagnet to turn on and off when asked - What are some examples of electromagnets? What makes an electromagnet useful? 

I found this fun little video from the movie Brave Little Toaster showing an electromagnetic in use at the junkyard.  

 

I ask students again - What makes an electromagnet useful? I am looking for answers that include unlike permanent magnets, electromagnets can be turned off and on. How does an electromagnet work? An electric current produces a magnetic field, as long as electricity is supplied there is magnetism.

In the lesson we learned that when the electric current is added, the atoms line up in the same direction creating a magnetic field. Using this understanding of the atoms, what is the difference between a permanent magnet and an electromagnet? A permanent magnet atoms are always line up in the same direction. An electromagnet atoms line up only when the electric current is flowing.

I want to reinforce the learning for my students be providing them another way to measure the magnetism of the electromagnet. I select Magnets and Electromagnets from the PhET Interactive Simulations website. My goals for my students are two-fold. They experience an alternative representation connecting magnets and electromagnets and they connect the hands-on learning with a virtual experience deepening student conceptual understanding.

PhET Electromagnet Simulation

As students work with the virtual lab, I monitor their progress and ask how the compass is being used to show a magnetic field and what do they notice about the electrons? Students notice the movement of the compass needle near the electromagnet points to the north or south depending on the end of the electromagnet. I ask them to click on the Bar Magnet tab and compare the movement of the compass needle. Also, I encourage students to note the difference between DC and AC current.