Name: ______________________________Date: _______________AP Physics C Force and Magnetic Field

Introduction:

In this lab, we will use the formula for magnetic force Fb = IBL in order to derive the magnetic field produced by the magnets. We will run a current through a metal loop, place a magnetic field perpendicular to the wire, and as a result we will create a magnetic force on the loop of wire. However, according to Newton’s Third Law, every force must have an equal and opposite reaction force; in this case the reaction force pushes down on the magnet. Since the magnetic force on the wire and magnet are equal, we can set them equal to each other, and find a relationship between the Normal Force on the magnet, current, magnetic field, and wire length (done in derivation section), and calculate the magnetic field. Derivation: FN- W - Fb = 0FN = Fb + WFN = IBL + W

(Similar to y = mx + b where m = BL and b = W)

*W is the weight of the magnet(s)Materials:· Rheostat· Alligator clips· Battery· Ammeter· PASCO Current Balance· PASCO Current loops· Magnets· Electronic balance

Procedure:

1. First get the PASCO Current Balance and place it on a flat surface such as a table.2. Place the current loop with length of 1 cm inside the side holder.3. Place the bar of magnets on an electronic balance and turn it on. Then, press the “On/Off

Zero” button to reset the weight measurement to 0.00g. 4. Place the current loop inside the bar of magnets.

5. Connect the alligator clips in this order:a. Connect one Alligator Clip from the positive side of the battery to the right side of

the top holder.b. Connect another Alligator Clip from the negative side of the battery to the

positive (red) side labeled “1” on the ammeter.c. Now, take another Alligator Clip from the negative side of the ammeter and place

it on the right side of the rheostat.d. Attach one from the other side of the rheostat to the left side of the top holder.

6. Measure the weight of the magnets without the current running through the system and record it in each second column.

7. Set the scale to zero with the magnets on it, connect the circuit, place the current loop through the magnet, make sure that a current is flowing, adjust the rheostat until the balance reads 0.1 grams and record the current I in the table. Also do this for 0.2 grams and 0.3 grams.

8. Graph the results from the data table.

Data Table:

Weight W without current = __________N

Weight: w (N) Fn = W + w (N) Current: I (Amps)

0.1x10-3 _____x10-3

0.2x10-3 _____x10-3

0.3x10-3 _____x10-3

Plot:Fn (vertical axis) vs. Current (horizontal axis)

Analysis:

1. Draw the line of best fit.2. The slope of this line is _______.3. Knowing Fn = (LB/g)I + W ------> ΔFn = (LB/g)ΔI + W, solve for B in teslas:

B = ________T.

Post-Lab Questions:

1. What effect can a magnet of different size or shape have on the net force and torque if it was replaced with the bar of magnet used above? Would it not matter or would it have a significant effect on the net force?

2. Why did we need to use a rheostat in our experiment? Explain.

3. Instead of varying the current of the bridge, what is another way we could find magnetic field through the slope of a graph?

4. What are some potential sources of errors that could have caused an error in your graph and results?

Works Cited● http://www.physics.rutgers.edu/ugrad/labs/summer/magnetic