Strength of a Magnet's Field (B)
Obj:
Determine bar magnet's field strength (Bm).

Methods
1.  Place the compass at the 50.0 cm mark on the meter stick with its N-S poles aligned with the earth's magnetic field and perpendicular to the meter stick.
2.  Place the N pole of your bar magnet 45 cm away along the length of the meter stick; record θ on the compass.
3.  Move the magnet 5 cm towards the compass and record θ.
4.  Repeat until θ reaches approximately 70o.

Results and Analysis
1.  Plot tan θ vs.distance (x-axis), then draw a smooth line through the data points.
2.  Determine the distance where Bmagnet  = Bearth.  [Note:  Be  =  1.8 x 10-5 Teslas horizontal to the earth.]
3.  Allow tan θ = Bm/Be, then find Bm at 25 cm.
4.  Using tangent functions, at what distance is the magnet's field strength twice that of the earth?...half the strength?
5.  What relationship exists between distance and the magnetic field strength?
6.  Walk your compass slowly through the metal doorway leading into the hall and explain the results.                                                                                                                                             Magnet Man

Back to the Brockport High School Science Department