Physics 360 Neumann

VL 6 -Magnetic Fields & Forces

“Magnetic Field Strength of a Permanent Magnet”

Purpose

To examine properties of magnetic fields produced by magnetic dipoles.

Quantitative & Qualitative Objectives

• Discover the relationship between magnetic field strength and distance from a permanent magnet.

• Use the relationship to make and test predictions about the magnetic field strength.

Note: This lab has already performed for you. You may benefit from gaining a qualitative perspective before

continuing with the lab by exploring the Magnets & Electromagnets PHET here:

https://phet.colorado.edu/sims/cheerpj/faraday/latest/faraday.html?simulation=magnets-and-electromagnets

The procedure (in gray) below is included so that you may understand how the data provided was collected.

Procedure

1. Connect the magnetic field sensor to the data collection system and create a digits display of the X Magnetic Field

Strength.

2. Place the meter stick on a table so that the 100 cm end points North. You can use a compass or a map to find North.

Another option is to place your magnet on its edge. It will turn until its “north seeking pole” is pointing North. This

will reduce the effect of the Earth’s magnetic field on your measurements and make it easier to keep the magnet

stationary.

3. Place the magnetic field sensor on the meter stick so the actual sensor is at 3.0 cm. The actual sensor is indicated

by a circle with a dot in it on the probe of the magnetic field sensor.

4. Place the magnet on its edge at the end of the meter stick, so that the north

pole of the magnet is facing north. Note that this experiment only measures

magnetic field along the axis of this permanent magnet.

5. Start recording data, for different positions (see data table below).

Data

Distance

(m)

Magnetic

Field

Strength

(G)

Inverse cube

of Distance

(1/m3

)

0.030 49.2

0.035 32.5

0.040 22.7

0.045 15.7

0.050 12.0

0.055 8.7

0.060 7.0

Analysis

6. Look up the definition of the unit G of magnetic field. What does it mean, and how does it convert to T?

7. Based on the trend shown by the magnetic field strength measurements, will a graph of magnetic field strength

versus distance be linear? Explain your reasoning below.

8. Transfer the data to Excel, and create a graph with magnetic field strength (G) on the vertical axis and distance (m)

on the horizontal axis. Don’t forget to label the graph and the axes.

9. What does the graph tell you about the magnetic field strength as the distance increases? Is this relationship

linear?

10. Use Excel to create a best-fit curve – use Power trendline, and display the equation and the R2

value on your graph.

11. Complete the inverse-cube of the distance column in the table above by dividing 1 by the cube of each distance.

You can have Excel do that, but make sure to somehow include that result in your report.

12. Create a graph with magnetic field strength on the vertical axis and inverse-cube of the distance on the horizontal

axis.

13. What does the graph tell you about the magnetic field strength as the inverse-cube of distance increases?

14. The relationship between magnetic field strength and the inverse-cube of distance shown by your data in the

second graph should be linear. Use Excel to create a best-fit line – use Linear trendline, and display the equation

and the R2

value on your graph.

15. Think back to you first graph (Power). What does exponent of the Power equation actually mean, now that you

have created a linear graph as well? What should the exponent be?

16. Calculate the percent error between the exponent on your Power graph and the expected value of the exponent.

17. Think about what the slope and the intercept of the linear graph actually mean, and explain it. Hint: think of the

units!

18. Using the equation for the linear graph, predict the magnetic field strength for a distance of 0.09 m. Show your

work!

19. The Earth’s magnetic field is similar to the magnetic field of a permanent magnet. It protects astronauts in orbit

from radiation by deflecting charged particles in cosmic rays away from the Earth. Explain why NASA is concerned

about increased radiation exposure to astronauts as they explore further away from the Earth. Use the data from

this experiment to support your argument.

20. Superconducting magnets can be used to levitate trains allowing them to move with no friction. The distance that

the train is levitated above the magnetic track can vary from 1 cm to 10 cm. How would you expect the amount

of levitation of an empty train to compare with one that is fully loaded? Explain your reasoning below. Use the

data from this experiment to support your argument.

Don’t forget to attach both graphs to this lab.