11-02-2013, 11:27 AM
TO STUDY THE STRENGTH OF THE EARTH’S MAGNETIC FIELD.
TO STUDY THE STRENGTH.docx (Size: 576 KB / Downloads: 57)
THEORY
The magnetic field of the earth is thought to be caused by convection currents in the outer core of the earth working in concert with the rotation of the earth. The field has a shape very similar to the field produced by a bar magnet. However, the north magnetic pole (the north geo-magnetic pole) of the earth does not coincide with the north geographic pole. In fact, the north geo-magnetic pole (where the magnetic field lines emerge) is located close to the Earth's South Pole, while the geo-magnetic-south Pole is located in Northern-most Canada. Since the North Pole of a compass points towards the Earth's geomagnetic south pole, the determination of "true North" requires an angular correction known as the magnetic declination. In addition to the off-axis nature of the Earth's magnetic fields, the field lines also leave and enter the earth's surface at an angle (the magnetic dip angle).
Analysis:
1. Use Eq. 3 to calculate the horizontal component of the earth's magnetic field by plotting Bc vs. tanθ, or
so that Be will be the slope of your plot. Display your results graphically and determine Be from the your "best fit" straight line.
2. In this experiment, however, you are not calculating Be directly from a single equation, and one set of independent variables. Instead, you are performing a "best fit" from several data points. This implies that the best method for determining ΔBe is to determine the maximum and minimum slopes that fit your data points. In doing so, be sure to include the uncertainties in the current and angle in creating your new ranges (i.e. graph Bc(I + ΔI) vs. tan(θ + Δθ). Determine the values of Be max and Be min that are consistent with your data. Does the accepted value fall within this range?
3. Is there a particular angle θ at which you could suggest making measurements so as to minimize the angular uncertainty?