A 50-L electrical radiator containing heating oil is placed in a 50-m³ room. Both the room and the oil in the radiator are initially at 5°C. The radiator with a rating of 3 kW is now turned on. At the same time, heat is lost from the room at an average rate of 0.3 kJ/s. After some time, the average temperature is measured to be 20°C for the air in the room, and 60°C for the oil in the radiator. Taking the density and the specific heat of the oil to be 950kg/m³ and 2.2kJ/(kg °C), respectively, determine how long the heater is kept on. Assume the room is well-sealed so that there are no air leaks.

1. An unknown lamp placed 6m from a photometer screen provides the same illuminance as a 90 cd lamp placed 4 m from the screen.  What is the candlepower of the unknown lamp? 2. The illuminance of a room 20 ft x 15 ft is being designed.  The illuminance required is 50 footcandles.  What is the total required lumens output of the lamp assuming room and luminaire efficiency of 42%?

Q. 1/ piece of copper, whose length is 10 cm and the area of its section is 6 cm2. Fix one end of it on 150c and make the other end tangent to a piece of iron of 8cm length and equal to it with the cross-sectional area and straight to one, and the temperature of the piece of iron was 20c. Calculate the contact point temperature between the two pieces, noting that the thermal conductivity coefficient of copper is Scmc / [0.85, while for iron it is 0.75] / ScmC.