We want to design an electric space heater to operate from 120V. Two heating elements with resistances R1 and R2 are to be used that can be operated in parallel, separately, or in series. The highest power is to be 1200 watts and the lowest power is to be 300 watts. What values are needed for R1 and R2? What intermediate power setting is available?

The y form of iron is known as: a) ferrite b) cementite c) perlite d) austenite

Coiled springs ought to be very strong and stiff. si3n4 is a strong, stiff material. would you select this material for a spring? explain.

Along 8-cm diameter steam pipe whose external surface temperature is 900c connects two buildings. the pipe is exposed to ambient air at 70c with a wind speed of 50 km/hr blowing across the pipe. determine the heat loss from the pipe per unit length. (b) air at 500c enters a section of a rectangular duct (15 cm x 20 cm) at an average velocity of 7 m/s. if the walls of the duct are maintained at 100c. a) the length of the tube for an exit temperature of the air to be 40 0c. b)the rate of heat transfer from the air. c) the fan power needed to overcome the pressure drop in this section of the duct.