Problem: To minimize overall weight and size, miniature PM motors may use high energy magnets made with neodymium or other strategic elements; most such are neodymium-iron-boron alloy. With their higher flux density, electric machines with high-energy PMs are at least competitive with all optimally designed singly-fed synchronous and induction electric machines. Miniature motors resemble the structure in the illustration, except that they have at least three rotor poles (to ensure starting, regardless of rotor position) and their outer housing is a steel tube that magnetically links the exteriors of the curved field magnets.
What does the outer housing of a miniature motor resemble?
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Answer: steel tube


Problem: Most electrification systems use overhead wires, but third rail is an option up to about 1,200 V. Third rail systems exclusively use DC distribution. The use of AC is not feasible because the dimensions of a third rail are physically very large compared with the skin depth that the alternating current penetrates to (0.3 millimetres or 0.012 inches) in a steel rail). This effect makes the resistance per unit length unacceptably high compared with the use of DC. Third rail is more compact than overhead wires and can be used in smaller-diameter tunnels, an important factor for subway systems.
What is more prefferable for subway lines?
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Answer: Third rail


Problem: Different cultures have evolved various ways of creating clothes out of cloth. One approach simply involves draping the cloth. Many people wore, and still wear, garments consisting of rectangles of cloth wrapped to fit – for example, the dhoti for men and the sari for women in the Indian subcontinent, the Scottish kilt or the Javanese sarong. The clothes may simply be tied up, as is the case of the first two garments; or pins or belts hold the garments in place, as in the case of the latter two. The precious cloth remains uncut, and people of various sizes or the same person at different sizes can wear the garment.
Various cultures have come up with ways of making clothes from what?
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Answer:
cloth