The frequency of a microwave signal is 9.76 GHz. What is its wavelength? (c = 3.00 × 108 m/s)
A) 3.07 cm
B) 2.07 cm
C) 1.07 cm
D) 5.07 cm
E) 4.07 cm
A
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A comet entering the inner solar system from afar will
a. form a tail and some time later form a coma. b. form a coma and some time later form a tail c. always form a tail, but only sometimes form a coma
Brown dwarfs have
A) very narrow habitable zones B) no habitable zones C) very wide habitable zones D) habitable zones similar to the Sun
What are coronal holes?
What will be an ideal response?
A copper wire, 0.8 mm OD, 5 cm long, is placed in an air stream whose temperature rises at a rate given by Tair = (10+ 14t)°C, where t is the time in seconds. If the initial temperature of the wire is 10°C, determine its temperature after 2 s, 10 s and 1 min. The heat transfer coefficient between the air and the wire is 40 W/(m2 K).
GIVEN
• A copper wire is placed in an air stream
• Wire diameter (D) = 0.8 mm=8*10-4 m
• Wire length (L) = 5 cm=0.05 m
• Air stream temperature is: Tair = (10 + 14t)°C
• The initial temperature of the wire (To) = 10°C
• The heat transfer coefficient ( )ch = 40 W/(m2 K)
FIND
• The wire temperature after 2 s, 10 s and 1 min
ASSUMPTIONS
• Constant and uniform heat transfer coefficient
SKETCH
PROPERTIES AND CONSTANTS
For copper at 127°C
• Thermal conductivity (k) = 383 W/(m K)
• Density (?) = 8933 kg/m3
• Specific heat (c) = 383 J/(kg K)