Electro-magnets are created
a) applying a charge to a magnetic material, wrapped in an insulator, which creates an electro magnetic field around the magnet.
b) covering a magnet with insulation in applying an alternating electrical current to the magnet.
c) twisting a ferromagnetic material, wrapping in an insulator, and applying a direct current to the coil.
d) wrapping in insulated wire around a medal with ferromagnetic properties and applying an electric current.

If forces acting on an object are unbalanced, which factors may result fron an unbalanced force? check all that apply

Clothing made of several thin layers of fabric with trapped air in between, often called ski clothing, is commonly used in cold climates because it is light, fashionable, and a very effective thermal insulator. so it is no surprise that such clothing has largely replaced thickand heavy old-fashioned coats. (a) consider a jacket made of five layers of 0.1-mm-thick synthetic fabric (k = 0.13 w/m·°c) with 1.5-mm-thick air space (k = 0.026 w/m·°c) between the layers. assuming the inner surface temperature of the jacket to be 28°c and the surface area to be 1.25 m2, determine the rate of heat loss through the jacket when the temperature of the outdoors is 0°c and the heat transfer coefficient at the outer surface is 25 w/m2·°c. (b) what would your response be if the jacket is made of a single layer of 0.5-mm-thick synthetic fabric? what should be the thickness of a wool fabric (k = 0.035 w/m·°c) if the person is to achieve the same level of thermal comfort wearing a thick wool coat instead of a five-layer ski jacket?

What is special about a dc circuit ?