A compound lens is made by joining the plane surfaces of two thin plano-convex lenses of different glasses. The radius of curvature of each convex surface is 80 cm. The indices of refraction of the two glasses are 1.50 and 1.60
What is the focal length of the compound lens?
A) 71 B) 75 C) 67 D) 69 E) 73
E
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Blackbody radiation is from a body that
A) does not emit radiation in the visible. B) is black. C) deflects all radiation falling on it. D) absorbs all radiation falling on it. E) is actually white.
Liquid mercury at a temperature of 315°C flows at a velocity of 10 cm/s over a staggered bank of 5/8-in. 16 BWG stainless steel tubes, arranged in an equilateral triangular array with a pitch-to-diameter ratio of 1.375. If water at 2 atm pressure is being evaporated inside the tubes, estimate the average rate of heat transfer to the water per meter length of the bank, if the bank is 10 rows deep and contains 60 tubes. The boiling heat transfer coefficient is 20,000 W/(m2 K).
GIVEN
Liquid mercury flow over an equilaterally staggered tube bank
Inlet mercury temperature (Tm,in) = 315°C
Mercury velocity (Us) = 10 cm/s = 0.1 m/s
Tubes are 5/8 in., 26 BWG stainless steel
Pitch to diameter ratio (S/D) = 1.375
Water at 2 atm pressure is being evaporated within the tubes
Number of rows of tubes (N) = 10
Number of tubes (Nt) = 60
boiling heat transfer coefficient (bh) = 20,000 W/(m2 K)
FIND
The average rate of heat transfer per meter length of the bank (q/L)
ASSUMPTIONS
Steady state
Tubes are type 304 stainless steel
Temperature change of the mercury across the tube bank is negligible
SKETCH
PROPERTIES AND CONSTANTS
the saturation temperature of water at 2 atm (2.02 x 105 Pa) is Tw = 120°C
Outside diameter (Do) 5/8 in. = 0.0159 m
Inside diameter (Di) = 0.495 in. = 0.0126 m
the thermal conductivity of type 304 stainless steel (ks) = 14.4 W/(m K) at 20°C
Three flat layers of transparent material are stacked upon one another. The top layer has index of refraction n1, the middle n2, and the bottom one n3 . If n1 > n2 > n3, and a ray of light in air strikes the top layer, at which surface given can total internal reflection occur first?
a. the top surface b. the surface between materials with indices n1 and n2 c. the surface between materials with indices n2 and n3 d. Total internal reflection cannot occur at any of these surfaces.
Ann the Astronaut weighs 65.0 kg. She is space walking outside the space shuttle and pushes a 350.0-kg satellite away from the shuttle at 0.70 m/s. What speed does this give Ann as she moves toward the shuttle?
a. 0.13 m/s b. 3.8 m/s c. 590 m/s d. 290 m/s e. 7.7 m/s