Clouds that appear dark in visible light often glow when observed at long infrared wavelengths
Indicate whether the statement is true or false
TRUE
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An electrical transmission line of 1.2 cm diameter carries a current of 200 Amps and has a resistance of 3 × 10–4 ohm per meter of length. If the air around this line is at 16°C, determine the surface temperature on a windy day, assuming a wind blows across the line at 33 km/h.
GIVEN
• An electrical transmission line on a windy day
• Line outside diameter (D) = 12 cm = 0.012 m
• Current (I) = 200b Amps
• Resistance per unit length (Re/L) = 3 × 10–4 ohm/m
• Air temperature (Tb) = 16°C
• Air velocity (V) = 33 km/h = 9.17 m/s
FIND
• The line surface temperature (Ts) ASSUMPTIONS
• Steady state conditions
• Air flow approaching line has low free-stream turbulence
SKETCH
PROPERTIES AND CONSTANTS
Thermal conductivity (k) = 0.0248 W/(m K) Kinematic viscosity (?) = 15.3 × 10–6 m2/s Prandtl number (Pr) = 0.71
A diffraction grating has 300 lines per mm. If light of wavelength 630 nm is sent through this grating, what is the highest order maximum that will appear?
A) 8 B) 2 C) 6 D) 5 E) 5.3
You hold an apple in one hand and an orange in the other. If you doubled the mass of the apple and tripled the mass of the orange, without changing the distance between them, the gravitational force between them would be
A) unchanged, because it is zero both before and after the mass alterations. B) five times larger. C) doubled. D) three times larger. E) six times larger.
A 0.28-kg stone you throw rises 34.3 m in the air. The impulse your hand receives from the stone while it throws the stone is
a. 2.7 N s, up. b. 2.7 N s, down. c. 7.3 N s, up. d. 7.3 N s, down. e. 9.6 N s, up.