The Stefan – Balletomane law gives the radiant energy emitted or absorbed by an object: Radiation Ex: The sun shines directly on one side of a flat black panel on a spacecraft which has an area of 5. 0 mm and an impassivity Off = 0. 95. The spacecraft is located 1. 5 0 1011 m from the sun.

How much power does the panel absorb from the sun if the sun is considered to be an ideal blackbody with a temperature of 5700 K? Assuming that the panel can only lose energy through radiation, what is the equilibrium temperature of the panel? A: The total power emitted by the sun is given by equation 13. 2 with , the surface temperature of the sun. The radius of the sun is . This energy spreads out over the surface of a sphere of radius, r, so that the amount reaching the panel is : The panel is in equilibrium if its temperature, Tap, remains constant.

This means that the panel is losing as much power as it is gaining. It gains energy only through the one sunlit side, but it can radiate energy from both sides. Thermodynamics The first law of thermodynamics is The efficiency e of a heat engine is Ex: An ideal gas performs 550 J of work while losing 150 cal of heat energy. What are the values of W, Q and ? What happens to the temperature of the system during the process? A: The work done is W= +550], since the system does the work. The heat transferred is Carrot’s Principle and the Carrot Engine Ex: A Carrot engine as an efficiency of 0. 00, and the temperature of its cold reservoir is 105 co. (a) Determine the Kelvin temperature of its hot reservoir. (b) If 1. 25 kcal of heat are rejected to the cold reservoir, what amount of heat is put into the engine? Refrigerators, Air Conditioners, and Heat Pumps Ex: A Carrot air conditioner uses 15 400 J of electrical energy to cool a house down to 22 co when the outdoor temperature is 36 co. How much heat is deposited outdoors? A: First find the ratio of the heats ICQ and Q, where and . Thus, . But , so that . As a result