The cost of a kilowatt hour of energy in the bill is 0.20 euros. A cylindrical led bulb of 5 W has a luminous flux of 50 lm. What is the luminous efficiency of this light source? Knowing that the bulb is 5cm long, 36mm in diameter, and plugged into a 220V socket, what is the resistivity of the bulb? How much would you spend in a year if you used 5 LED bulbs all on for 12 hours a day?

Air is contained in a variable-load piston-cylinder device equipped with a paddle wheel. initially, air is at 400 kpa and 17°c. the paddle wheel is now turned by an external electric motor until 75 kj/kg of work has been transferred to air. during this process, heat is transferred to maintain a constant air temperature while allowing the gas volume to triple. calculate the required amount of heat transfer in kj/kg.