| | Essential questions | | How does a force field indicate the forces acting on an object?
What is the shape of the magnetic field around a bar magnet? | |
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We use magnets and magnetized objects every day, often without realizing it. All around us is a magnetic field—the Earth’s magnetic field. How do these magnetic forces and fields work? In this investigation, you will explore the magnetic field surrounding a bar magnet and compare it to the Earth’s magnetic field. Magnetic fields are measured in units of teslas (T). 
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Part 1: Tracing the magnetic field of a bar magnet
- Launch the magnetic field interactive simulation and select the bar magnet option.
- Pass your mouse over the diagram to reveal the magnetic field line vectors.
- Find a few positions close to the north magnetic pole of the magnet from which you can follow the field arrows all the way to the south magnetic pole. Sketch the paths you followed.
- What does the direction and length of each field arrow indicate?
- Determine the strength and direction of the magnetic field 5 cm to the right of the bar magnet’s middle, 5 cm to the left the bar magnet’s middle, and 5 cm above the bar magnet’s middle.
- If you increase the strength of the bar magnet, what happens to the magnetic field lines?
- What is the meaning of the paths from north to south magnetic pole that you sketched out?
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In this interactive simulation, you will investigate the magnetic field of a bar magnet (Part 1) and the Earth (Part 2). Vector arrows representing the magnetic field are revealed by passing your mouse over parts of the display window. The value of the magnetic field at any particular point is displayed in the lower left-hand corner of the simulation.
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Part 2: Earth’s magnetic field
- In the interactive simulation, click on the button to select the Earth’s magnetic field option.
- Pass your mouse over the diagram to reveal the magnetic field line vectors.
- Find Earth’s north and south magnetic poles.
- What is the strength of Earth’s magnetic field near one pole (location #1 in the figure)? Near the other pole (#2)? Near the equator (#3)?
- Where are Earth’s north and south magnetic poles? Explain using magnetic field lines.
- How does the strength of Earth’s magnetic field near its surface compare to the field 5 cm from the bar magnet that you measured in the previous part?
- Research online the strength of Earth’s magnetic field and compare to your results in Question a above.
Part 3: Magnetic field of a bar magnet using iron filings
Have your partner place a bar magnet under a piece of poster board. Now sprinkle iron filings on the board. How can you use iron filings to locate the poles of the bar magnet?
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