Randolph College

Physics 116 Lab

Properties of electricity and Magnetism

Lab Manual Home

Part 1

Equipment

· D-cell battery in holder

· Wire (at least 2 feet – clip together two or three wires)

· Compass

In this lab, you will determine the relative strength of a magnetic field as a function of distance from a wire.

Important safety note: In this lab, you will be connecting the two ends of a battery to each other with a single wire and no load. If the wire is left connected for long periods of time, the battery will become extremely hot, as will the wire. For your safety, wear safety goggles in this experiment and do not have the wire connected for more than 15 second intervals.

Procedure:

1. Make a data sheet for your compass. Cut a square piece of paper 10 cm by 10 cm. Divide the paper into quadrants by drawing two perpendicular lines with the intersection at the center of the paper. Label the quadrants as shown in figure 1 below.

2. Place the paper on a platform that will support the compass and allow you to write on the data as well. (A small piece of cardboard or plastic would suffice)

3. Use the compass to determine which direction is north in your room. Orient the wire so that the wire runs north-south.

4. Connect the positive end of the battery to the north end of the wire and the negative end of the wire to the south end of the battery. Lay the compass with the center of the compass at the intersection point of the perpendicular lines on your data sheet. Place this on top of the wire and mark at the edge of the compass the position of the compass needle. This will be a data point for a 0.5 cm position

5. Disconnect the wire and let the system cool for 60 seconds.

6. Repeat step 2, this time holding the compass/platform 2 cm above the wire, and record the reading in the data table.

7. Disconnect the wire and let the system cool for 60 seconds.

8. Repeat the above procedure with measurements at 4 cm, 6 cm, 8 cm, and 10 cm. Disconnect the wire between each measurement, and when you are done with the final measurement.

Figure 1 (from Tangent Galvonometer, Laying the Foundation)

9. On your marking paper, carefully draw a line from the center of the compass (the intersection of the two perpendicular lines) through each of the points representing a needle position.

10. Draw a 5 cm line straight north from the intersection point. This represents the Earth’s magnetic field.

11. From the top of the 5 cm line, draw horizontal lines to each of the needle position lines you drew in step 9, as shown in Figure 2 below.

12. Measure the distance, in cm, of your horizontal lines you drew in step 11. This distance represents the relative strength of the magnetic field due to the wire at each position. Record these values in the data table below.

13. Make a plot of relative magnetic field strength vs. distance from the wire

14. What additional information would you need to calculate an exact value of magnetic field at a given position near the wire in your data table?

Part 2

This next portion of the lab will investigate the direction of the magnetic field around the wire.

1. Connect the apparatus as in steps 1-2 as above. Place the compass on top of the wire and record your reading below. Disconnect the wire and let the system cool.

2. Place the compass beneath the wire and record your reading below. Disconnect the wire and let the system cool.

3. Place the compass 5 cm to the left of the wire and record your reading below. Disconnect the wire and let the system cool.

4. Place the compass 5 cm to the left of the wire and record your reading below. Disconnect the wire and let the system cool.

For each data point, state the direction of the magnetic field. There are six possible answers for each position: North, south, west, east, into the page, and out of the page. How do you justify your answer to each direction?

Part 3

In this part of the lab, your task is to determine if the direction of the current in the wire has an effect on the direction of the magnetic field. Design a procedure and test the procedure.

Procedure

Conclusion

Part 4

Watch the video at

Explain why the magnets take much less time to fall through the copper tube than if the magnets are outside of the copper tube.




Part 5

There are some things around your house that exhibit magnetic properties, or produce magnetic fields, that you may not expect. Take your compass and explore. Try to find three things in your home, school, or business that the compass is attracted to or affected by. As a hint, try things that carry large electrical currents, or large metal objects that aren’t used much (like a filing cabinet or garage/shed door). Describe your findings below and hypothesize why these objects may be exhibiting magnetic properties.