Question

Results Neatly write up your calculations for H and B, either typewritten or neatly on engineering paper 1.1 Part A You should have identified a null point along the axis of the magnet where the magnetic fields due to the Earth and magnet cancel. Measure the distance from the null point to the center of your magnet (this will be our dis- tance r) Now BE and Bm are oppositely directed, and since it's a North null point, their vector sum must equal the field of the Earth (take this to be 0.2 Gauss, or 2 x 10-5 T) BE B and since the magnet generates a dipole field that is equivalent to being far away from a current-carrying coil 41a r sort of the equivalent (coil Find A, the magnetic dipole moment of the magnet current x area) combination to produce a B-field equal to the magnet. If the magnet really is a current loop of r 1 cm, how much current would have to flow to generate an equivalent B? Now that you know u, find the Bm strength (n Tesla) close (r 1 cm) to the magnet. 1.2 Part B Measure the r that gives a compass de ection from North of 0 700. Find Bm here Now double the distance to 2r and mea- sure the new compass deflection from North Calculate the Bm at this new distance. You might want to do this two or three times to get a consis North tent result. By what factor (roughly) did m decrease needle when r doubled? Assume B 1 /r what n is most consis tent with your measurements? Now from part B.1, you know the magnetic strength at r, and you also know how the field weakens with decreasing r. Use this to estimate the strength of the field r 1 cm from the magnet. Hopefully this roughly matches your result from A.3

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