Question 81. When the incident surface is a sphere, the projection of surface normal to the line of propagation is the silhouette disk of the sphere which is a circle of the diameter of

Question 82. The solid angle is defined by a region by the rays of a sphere, and is measured as

Question 83. If I n denotes the normal intensity and I α represents the intensity at angle α, then

Question 84. Consider two surfaces, one absolutely black and the other non-black. These surfaces are arranged parallel to each other and so close that the radiation of one falls totally on the other. Choose the correct option

Question 85. The plane angle is defined by a region by the rays of a circle, and is measured as

Question 86. Consider an enclosure formed by three surfaces having the following values of shape factors, emissivities and temperatures.
Surface 1 i.e. curved cylindrical has an emissivity 0.75 and temperature 800 K
Surface 2 i.e. closing disc has an emissivity 0.8 and temperature 700 K
Surface 3 i.e. closing disc has an emissivity 0.8 and temperature 700 K
The closing flat discs are 25 mm in diameter and they have interspacing distance equal to 100 mm. If the shape factor between these two identical discs is 0.05, calculate the net rate of radiant heat flow from the curve surface to each of the closing end surface.

Question 87. Figure depicts the variation of which two numbers?

Question 88. A perfectly black body

Question 89. The distribution of radiant energy is non uniform with respect to

Question 90. For a prescribed wavelength a black body radiates how much energy at the temperature of body?