Coffee beans are roasted by floating them with a column of hot air at 250°c. if the beans start at 22°c and are done when they reach 200°c, how long does this process takewith average convection of h =20 w/m2°c? assume the coffee beans have typical volume and surface areas of 44 mm3 and 66 mm2 respectively, a conductivity of 0.184 w/m°c, specific heat of 2.564 kj/kg °c and a density of 552 kg/m3. assume that the beans are relatively dry at the start of this process and evaporative losses can be neglected.

Antireflective coatings on solar cells are often made by applying a thin film of silicon nitride (sinx), which has an index of refractive of 1.2, on the top of the silicon solar cell, which has a refractive index of about 3.5. however, the sun emits radiation of various wavelengths which the solar cell absorbs, and the antireflective coating can only absolutely minimize the reflection of one of these wavelengths. the coating thickness is chosen to reduce the reflection of green/yellow light (e = 2.2 ev), which is the most intense color in the solar spectrum (shown below). which of the following coatings would minimize reflection of green/yellow light? the answer is 820 nm how? what is the angular width of the central maximum of an electron traveling at 2 x 108 m/s going through a single slit of width 1 mm.