The surface also exchanges heat with the surrounding walls of the enclosure by radiation. the total hemispherical emissivity of the surface is 0.9. the surface is completely surrounded so the surface behaves as if each portion of it interacts with a blackbody at the temperature of the enclosure walls. properties of the air are: k = 0.0261 w/mk, € ν =1.8 ×10−5 m 2 /s, pr = 0.73 and the stephan-boltzmann constant is € 5.67 ×10−8 w/m2 k4 . (a) determine the total heat flux from the surface at a location 4.5 cm from the lower edge. (b) sketch the variation of surface heat flux q” with x. (c) where is the absolute value of the surface heat flux smallest? (d) for this system, what is the asymptotic dependence of heat flux on x as the distance from the bottom becomes large?

Athin nonconducting rod with a uniform distribution of positive charge q is bent into a circle of radius r. the central perpendicular axis through the ring is a z-axis, with the origin at the center of the ring. a) what is the magnitude of the electric field due to the rod at z = 0? n/c (b) what is the magnitude of the electric field due to the rod at z = infinity? n/c (c) in terms of r, at what positive value of z is that magnitude maximum? r (d) if r = 4.00 cm and q = 9.00 µc, what is the maximum magnitude? n/c

People with normal vision cannot focus their eyes underwater if they aren't wearing a face mask or goggles and there is water in contact with their eyes. in a simplified model of the human eye, the aqueous and vitreous humors and the lens all have a refractive index of 1.40, and all the refraction occurs at the cornea, whose vertex is 2.60 cm from the retina.with the simplified model of the eye, what corrective lens (specified by focal length as measured in air) would be needed to enable a person underwater to focus an infinitely distant object? (be careful-the focal length of a lens underwater is not the same as in air! assume that the corrective lens has a refractive index of 1.62 and that the lens is used in eyeglasses, not goggles, so there is water on both sides of the lens. assume that the eyeglasses are 2.05cm in front of the eye.)

You have a resistor and a capacitor of unknown values. first, you charge the capacitor and discharge it through the resistor. by monitoring the capacitor voltage on an oscilloscope, you see that the voltage decays to half its initial value in 3.00 ms . you then use the resistor and capacitor to make a low-pass filter. what is the crossover frequency fc?