A separately excited DC motor turns at 1200 r/min when the armature is connected to 115V source. Calculate the armature voltage required so that the motor runs at 1500 r/min. At 100 r/min.

Aheat pump using refrigerant-134a heats a house by using underground water at 8°c as the heat source. the house is losing heat at a rate of 60,000 kj/h. the refrigerant enters the compressor at 280 kpa and 0°c, and it leaves at 1 mpa and 60°c. the refrigerant exits the condenser at 30°c. determine: (a) the power input to the heat pump, (b) the rate of heat absorption from the water, and (c) the increase in electric power input if an electric resistance heater is used instead of a heat pump