Magnetic Effect of Current

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Purpose

How does the magnetic field due to a current-carrying loop of wire change when we change:

(a)

(b)

(c)

Procedure

1. Place your compass on the center of the platform of the galvanometer and line up your galvanometer so that the loops of wire lie North-South.

   

2. Connect the power supply, ammeter, 5 W resistor, and loop of wire as shown above.
3. Increase the current in 0.1 A increments from 0 to 1.0 A, then 1.5 A and 2.0 A (as shown in the table below) and record the compass deflection (angle) from North (North = 0°), filling in the data table I as shown. CAUTION: The resistor can get hot if you leave the current on for too long.
4. Reverse the current and repeat, filling in data table II.
5. With all the coils wrapped around the galvanometer, produce a current of 1.0 A. Remove one coil at a time, and record the compass reading in each case in data table III.

Data Tables

I			II				III
Amps	Angle		Amps	Angle		Number of Coils	Angle
0			0			0
0.1			0.1			1
0.2			0.2			2
0.3			0.3			3
0.4			0.4			4
0.5			0.5			5
0.6			0.6			6
0.7			0.7			7
0.8			0.8			8
0.9			0.9			9
1			1			10
1.5			1.5
2			2

Questions

1. State the general relationship between the current through the coils and the deflection of the compass needle.

2. Is the compass needle really responding to the current in the loop, or something else? Explain.

3. Describe the two magnetic fields the compass is responding to, and draw a diagram with a vector representing each.

4. What happened to the compass needle when you reversed the current? What does this tell you about what happens to the magnetic field due to the current when you reverse the current? Draw a new sketch of the magnetic field vectors.

5. State a general relationship between the number of coils of wire and the compass deflection. What does this tell you about the magnetic field produced by several current-carrying wires compared to one current-carrying wire?