If I had a magnetic bar in space that was 2cm wide and 2cm high and was one Earth diameter long and had the same magnetic strength as the Earth, would the distribution of field lines be the same length and width as the Earth's field lines?
The magnetic field of the earth looks approximately like the field of a magnetic dipole with field values on the order of tens of micro Tesla. The magnetic field of a bar magnet also is essentially that of a magnetic dipole, so provided the bar magnetic creates a field that is also on the order of tens of micro Tesla, the field lines would look similar in length at given distances from the poles (not sure I understand what you mean by the width of field lines). There's a great image on the Wikipedia page for the magnetic field of the earth in which you can clearly see that the field looks very much like that of a magnetic dipole, especially away from its surface. One difference, however, is that since the magnetic field of the Earth is produced by molten iron whose motion is constantly changing its magnetic field, the magnetic field of a bar magnet is fixed.
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