The surface of Venus can be observed with
A) most amateur telescopes.
B) the Mt. Wilson 100" telescope.
C) the Hubble Space Telescope.
D) radar observations.
E) All of these have provided detailed observations about the surface of our sister planet.
D
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A 0.15-m-square circuit board is to be cooled in a vertical position, as shown in the sketch. The board is insulated on one side while on the other, 100 closely spaced square chips are mounted, each of which dissipated 0.06 W of heat. The board is exposed to air at 25°C and the maximum allowable chip temperature is 60°C. Investigate the following cooling options
(a) Natural convection
(b) Air cooling with upward flow at a velocity of 0.5 m/s
(c) Air cooling with downward flow at the velocity of 0.5 m/s
GIVEN
? Square vertical circuit board insulated on one side, chips on the other side
? Length of each side (L) = 0.15 m
? Heat dissipation per chip (q) = 0.06 W
? Number of chips (N) = 100
? Ambient air temperature (T?) = 25°C
? Maximum allowable chip temperature (Ts) = 60°C
FIND
Investigate the following cooling options
(a) Natural convection
(b) Forced air cooling with an upward air velocity (U?) = 0.5 m/s
(c) Forced air cooling with a downward air velocity (U?) = 0.5 m/s
ASSUMPTIONS
? Steady state
? Uniform surface temperature
? Radiative heat transfer is negligible
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 28, for dry air at the mean temperature of 42.5°C
The matter in white dwarfs is about a million times denser than matter around you, since you have packed the mass of the Sun into the volume of our Earth
Indicate whether the statement is true or false
Our home galaxy is called the ______________
Fill in the blank(s) with correct word
Diamond has an index of refraction of 2.419 . What is the critical angle for internal reflection inside a diamond that is in air?
a. 48.8° c. 24.4° b. 131° d. 155°