Determining the Relationship between the Strength of a Magnetic Field and the Current

PURPOSE: Find the relationship, or the lack thereof, between the strength of the magnetic field associated with a current and the current in the coil and the number of turns of the coil.

Thus from the graph, the relationship between the strength of the magnetic field associated with a current carrying coil and the number of turns of the coil can be defined as positive; as the number of turns of the coil increases, the strength of the magnetic field associated with the current carrying coil also increases.

HYPOTHESIS: The strength of the magnetic field associated with a current carrying coil and the number of turns of the coil are directly related. As the magnetic field gets stronger (measured by change in the degrees of the compass) increases the current will also increase. Similarly, the number of the turns of the coil increases and the strength of the magnetic field associated with the current carrying coil is also directly related. Both relationships will have positive linear relationship.

MATERIALS: * Compass * Ammeter * Power Supply * Plastic Toilet Paper Roll * Conductive Wires

PROCEDURE: 1. Obtain the materials. 2. Wrap the wire tightly around the plastic toilet paper roll 12 times. 3. Connect the wire to the ammeter with the green wire and then connect the ammeter to the power supply with the yellow wire. 4. Place a compass facing North perpendicular to the end of the plastic toilet paper roll. 5. Set the current to 0.4A and record the angle of rotation of the compass. 6. “Refresh” the compass by turning off the power supply. Make sure the compass is facing North again. 7. Repeat steps 3 to 6 with a current of 0.8 and 1.2.

B = (current * # of coils) / length of wire Number of turns of coil | Current (A)(x-axis | Degree Changes in Compass Needle from Equilibrium (degrees) | 10 | 0.15 | 6 | | 0.30 | 11 | | 0.45 | 17 | | 0.60 | 22 | | 0.75 | 27 | | 0.90 | 33 | 15 | 0.15 | 10 | | 0.30 | 21 | | 0.45 | 26 | | 0.60 | 35 | | 0.75 | 42 | | 0.90 | 50 | 20 | 0.15 | 12 | | 0.30 | 24 | | 0.45 | 35 | | 0.60 | 45 | | 0.75 | 53 | | 0.90 | 58 | 25 | 0.15 | 15 | | 0.30 | 29 | | 0.45 | 42 | | 0.60 | 53 | | 0.75 | 62 | | 0.90 | 69 |

GRAPHS: See attached. (strength of field vs. current and strength of field vs. angle from north)

Analysis:

In these graphs, the number of degrees the compass needle moved from equilibrium (indicating the strength of the magnetic field associated with the current carrying coil: greater degrees=stronger magnetic field and smaller degrees=weaker magnetic field) is graphed as a function of the current in the coil.
The lines of best fit indicate that there is a positive linear relationship between the current in the wire and the strength of the magnetic field associated with the current carrying wire; for N (number of turns of coil) =10, the degrees the compass needle moved from equilibrium increased from 6° to 11° to 17° and so on as the current in the wire increased from 0.15 A to 0.30 A to 0.45 A and so on; for N=15, the degrees the compass needle moved from equilibrium increased from 10° to 21° to 26° and so on as the current in the wire increased in a similar fashion as for N=10; for N=20 and N=25, a similar positive linear relationship is evident.
Thus, from the graph, the relationship between the strength of the magnetic field associated with a current carrying coil and the current in the coil can be defined as positively linear; as current in the coil