In most small electric motors, the magnIn most small electric motors, the magnets that are around the central rotor (the field magnets) are . The magnet in the center is a(n) .
A) horseshoe magnets, bar magnet
B) bar magnets, horseshoe magnet
C) electromagnets, permanent magnet
D) permanent magnets, electromagnet

Consider the growth of a 20-nm-diameter silicon nanowire onto a silicon wafer. the temperature of the wafer surface is maintained at 2400 k. assume the thermal conductivity of the silicon nanowire is 20 wm-1k-1 and all its surfaces including the tip are subjected to convection heat transfer with the coefficient h = 1×105 wm-2k-1 and t∞ = 8000 k. when the nanowire grows to l = 300 nm, what is the temperature of the nanowire tip (t (x =