Name: ______Day: ______@______

Magnetic Force

The magnetic field of a permanent magnet is due to the alignment of the material’s magnetic dipole moments. The strength of the field is an indication of the fraction of these moments aligning with each other. As such the field of a permanent magnet is constant. Note: BoAVE is determined from the average value calculated for Bo in each measurement for Part III.

Part I: Force vs. Current: Fo = ______kg x 9.8 m/s2 = ______N

Current (A) / “counter mass” (gm) / “counter force” (N) / FM (N)
0.5
1.0
2.0
3.0
4.0
5.0

a) “counter force” = b) FM = I L BoAVE =

Part II: Force vs. Length:

Length (m) / “counter mass” (gm) / “counter force” (N) / FM (N)

a) “counter force” = b) FM = I L BoAVE =

Part III: Force vs. B-Field:

No. / mass (I = 0) (gm) / Fo (N) / “mass” (gm) / “force” (N) / FM (N) / Bo (T)
1
2
3
4
5
6
AVE Bo

a) “force” = b) Bo =

Graphs: Make a graph for each part of this experiment. Put the force, F, on the y-axis, and I, L, and B on their respective x-axis.


Magnetic Force (cont’d.)

Question 1:

a) How many protons, on average per bundle, are accelerated at the Fermilab accelerator?

N = ______protons

b) What is the total charge of the bundle?

Q = ______C

c) What is the average current of the bundle? (assume the bundle travels at the speed of light)

I = ______A

d) Fermilab is a circle. Calculate the magnetic field, BF, at the center of Fermilab’s main ring.

BF = ______T

e) What is the percent difference between this value (from d above) and the Earth’s average magnetic field?

DB = ( BÅ – BF ) / BF * 100 = ______%

Question 2:

What is the magnitude of the magnetic force on all of the wires in the Empire State building? Assume there are 200 wires per floor each carrying 1.0 A of current which run vertically up the height of the building. Use BÅ = 5.5x10-5 T at 71° pointing downward.

Question 3: determine the mass of a 0.5 m Cu wire which could be balanced by the Earth’s magnetic field. Assume that the wire is carrying 2000 A of current and that BÅ = 0.2x10-5 T directed parallel to the surface of the Earth.