Which technology can allow a single ground-based telescope to achieve images as sharp as those from the Hubble Space Telescope?
A. adaptive optics
B. grazing incidence
C. interferometry
Ans: A. adaptive optics
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In a Young's experiment, the paths from the slits to a point on the screen differ in length, causing destructive interference at the point. Which of the following path differences would cause this destructive interference?
a. 3l/2 c. 5l b. 4l d. None of these choices.
On the Kelvin scale the temperature is proportional to the average kinetic energy of the atoms or molecules whose temperature is being measured
Indicate whether the statement is true or false
Snell's Law: Light enters glass from air. The angle of refraction will be
A. greater than the angle of incidence. B. equal to the angle of incidence. C. less than the angle of incidence.
An electronic circuit board is the shape of a flat plate 0.3 m × 0.3 m in plan-form and dissipates 15 W. It is placed in operation on an insulated surface in a horizontal position or at an angle of 45 degrees to horizontal, in both cases; it is in still air at 25°C. If the circuit fails above 60°C, determine if the two proposed installations are safe.
GIVEN
• A flat plate with insulated back, horizontal or at an angle of 45 degrees in still air
• Plate size (s × s) = 0.3 m × 0.3m
• Heat generation rate (qG) = 15 W
• Air temperature (T?) = 25°C
• Maximum plate temperature (Ts) = 60°C
FIND
• If the two plate positions are safe
ASSUMPTIONS
• Radiative heat transfer is negligible
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the mean temperature of 43°C
Thermal expansion coefficient (?) = 0.00316 1/K
Thermal conductivity (k) = 0.0267 W/(m K)
Kinematic viscosity (?) = 17.9 × 10–6 m2/s
Prandtl number (Pr) = 0.71