# Investigating the Magnetic Field in a Coil

Purpose: Investigate how the strength of the field is affected by the current flowing in a coiled wire.

Equipment:

1. Select a slinky and stretch it between two cardboard supports. Do not over stretch the slinky!!
2. Connect a DC power supply to the ends of the slinky.
3. Insert a Multi-meter into the circuit and connect it to measure the current.
4. Count the number of coils between the cardboard supports and record this value.
5. Measure the distance between the supports.
6. Assemble the CBL, TI-82, and magnetic field sensor: be sure that all cables are firmly and gently in place.
7. Support the sensor and place it in the center of the slinky.
8. Use the PHYSICS program in the calculator to collect data. Use the High(mTesla) setting and collect data with choice #3; TRIGGER/Prompt
9. Use the power supply to vary the current and record the magnetic field strength in L1 as you collect your data. Don't forget to record the current level for each reading.

Analysis:

1. Construct a graph of Current vs. Magnetic Field Strength. You may download L1 using the graph link or enter the data in a spreadsheet or graph on your calculator.
2. Find the equation that describes the relationship between Current and Magnetic Field Strength. Remember that y and x may not be used as variables and that units must accompany all constants. What is the meaning of the y-intercept and the slope of this graph?
3. Qualitatively explain why this relationship makes sense. Include an explanation of what current means and why doubling the current causes the resultant change in magnetic field strength.

Teacher Notes: I used the CBL to collect data but it could be collected on any computer interface. I also took data with an MPLI unit but found no advantage to collecting in this manner.

Sample data taken for current vs magnetic field. It was collected with a CBL, entered into a spreadsheet on Excel and graphed. This data could also be analyzed easily on the TI-82. Using the suggested program, the Field data is already stored in L1 and the coil / length could be calculated as it is added to a second list.

 Magnetic Field Current mTesla Amperes -0.038 0.5 0.025 1 0.059 1.5 0.099 2 0.139 2.5 0.174 3 0.223 3.5 0.271 4 0.308 4.5 0.327 5

Written by Christine Deyo, July 1997