A mountain top is an especially good site for infrared telescopes since:
A) there you are closer to celestial objects.
B) you are above most of the carbon dioxide and water vapor in the atmosphere.
C) the cold weather helps the sensitivity of infrared detectors.
D) less air above means better seeing in many cases.
E) All of the above are factors.
E
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A transformer is to be designed to increase the 30 kV (rms) output of a generator to the transmission line voltage of 345 kV (rms). If the primary winding has 60 turns, how many turns must the secondary have?
a. 57 c. 690 b. 6900 d. 11
The Hubble Space Telescope has been repaired
Indicate whether the statement is true or false
A stepped steel shaft with diameters d1 5 56 mm and d2 5 52 mm is twisted by torques T1 5 3.5 kN?m and T2 5 1.5 kN?m acting in opposite directions. The maximum shear stress is approximately:
(A) 54 MPa
(B) 58 MPa
(C) 62 MPa
(D) 79 MPa
A plane truss with span length L 5 4.5 m is constructed using cast iron pipes (E 5 170 GPa) with a cross-sectional area of 4500 mm2. The displacement of joint B cannot exceed 2.7 mm. The maximum value of loads P is approximately:
(A) 340 kN
(B) 460 kN
(C) 510 kN
(D) 600 kN