Why are strong magnets around the armature of a motor curved in shape?
Why are strong magnets around the armature of a motor curved in shape?
Well then. Suppose the two half-circular parts of the NN and SS poles were straight. Then the field lines inside the air gap as well as in the pieces of the magnet would all be parallel and have equal magnitude (∇∗B⃗ =0∇∗B→=0). Without an air gap (I'm still talking about two pieces of magnet without the circular shape), you would just have an ordinary magnet (SS to the left, NNto the right), with all field lines parallel (inside) but bigger in magnitude, because the air is more reluctant to let the field lines go through.
The two circular shapes "direct" the field lines towards the round piece of metal inside, and even if there was only air between the two pieces, the field lines would converge (though ∇∗B⃗ =0∇∗B→=0would still apply). It concentrates them, so to speak. The magnitude of the field without the central metal piece would again be smaller because air is much more reluctant than metal to let the field lines pass.
The field lines at the circular surfaces come out (or go in) perpendicular to those surfaces, just like they do in the circle in the middle. So the lines are squeezed inside the middle part and do certainly not go straight.
In short, the boundaries of the metal parts make the lines non-straight.
Well then. Suppose the two half-circular parts of the NN and SS poles were straight. Then the field lines inside the air gap as well as in the pieces of the magnet would all be parallel and have equal magnitude (∇∗B⃗ =0∇∗B→=0). Without an air gap (I'm still talking about two pieces of magnet without the circular shape), you would just have an ordinary magnet (SS to the left, NNto the right), with all field lines parallel (inside) but bigger in magnitude, because the air is more reluctant to let the field lines go through.
The two circular shapes "direct" the field lines towards the round piece of metal inside, and even if there was only air between the two pieces, the field lines would converge (though ∇∗B⃗ =0∇∗B→=0would still apply). It concentrates them, so to speak. The magnitude of the field without the central metal piece would again be smaller because air is much more reluctant than metal to let the field lines pass.
The field lines at the circular surfaces come out (or go in) perpendicular to those surfaces, just like they do in the circle in the middle. So the lines are squeezed inside the middle part and do certainly not go straight.
In short, the boundaries of the metal parts make the lines non-straight.
