Final answer:
Concentric circles best represent the magnetic field lines around a magnet, as they show the direction and magnitude of the magnetic force with continuous loops both inside and outside the magnet. Straight lines, disconnected dots, and wavy lines do not accurately represent magnetic field lines.
Step-by-step explanation:
The best representation for the magnetic field lines around a magnet from the given choices is concentric circles (b). When mapping the magnetic field around a bar magnet using small compasses, they point in the direction away from the north pole of the magnet and toward the south pole, indicating that magnetic field lines form continuous curves rather than straight lines, disconnected dots, or wavy lines. Further, these lines are continuous, showing the magnetic force direction, and they form closed loops inside and outside the magnet, indicating the magnitude and direction of this force. The strength of the magnetic field is indicated by the density of these lines: the closer the lines are to each other, the stronger the magnetic force in that area.
Magnetic field lines are not just outside the magnet; they exist inside as well, forming continuous loops that confirm choice (b) over (d). They are not disconnected dots (c) or wavy lines (d) but are rather smooth continuous curves that loop back into the magnet, creating a complete circuit. The direction of the magnetic field around a long straight wire carrying an electric current also forms concentric circles, further supporting the characteristic shape of magnetic field lines.