The radiation curve is a plot of light intensity versus frequency for an incandescent source. If this light is first passed through a cool gas, the resulting radiation curve would most probable look like
1) I.
2) II.
3) III.
This best illustrates that the atoms of gas have
4) been excited.
5) absorbed part of the light.
6) simplified selective frequencies of the transmitted light.
Answer: 2, 5
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Addition by 1. Components: The figure shows four vectors, 
, 
, 
, and 
, having magnitudes 12.0 m, 10.0 m, 8.0 m, and 4.0 m, respectively. The sum of these four vectors is 
A. 16.4 m at an angle 77.8° with respect to +x-axis. B. 16.4 m at an angle 12.3° with respect to +x-axis. C. 19.5 m at an angle 77.8° with respect to +x-axis. D. 19.5 m at an angle 12.3° with respect to +x-axis. E. 8.20 m at an angle 77.8° with respect to +x-axis.
Suppose an engineer suggests that air instead of water could flow through the tube and the velocity of the air could be increased until the heat transfer coefficient with the air equals that obtained with water at 1.5 m/s. Determine the velocity required and comment on the feasibility of the engineer’s suggestion. Note that the speed of sound in air at 100°C is 387 m/s.
GIVEN
• Air flow through a tube
• Bulk inlet air temperature (Tb,in) = 93°C
• Tube diameter (D) = 0.015 m
• Tube length (L) = 0.3 m
• Tube surface temperature (Ts) = 204°C
• From Problem 7.32: h ,c L = 13,037 W/(m2 K)
FIND
• The velocity (V) required to obtain h ,c L = 13,037 W/(m2 K)
ASSUMPTIONS
• Steady state
• Constant and uniform tube temperature
SKETCH
PROPERTIES AND CONSTANTS
for dry air at the inlet bulk temperature of 93°C
Thermal conductivity (k) = 0.0302 W/(m K)
Kinematic viscosity (?) = 22.9 × 10–6 m2/s
Prandtl number (Pr) = 0.71
The major chemical component of the air we breathe today was deposited on Earth primarily via
a. volcanic eruptions. b. cometary impacts. c. asteroid impacts. d. chemical reactions in Earth's oceans.
An 800-N billboard worker stands on a 4.0-m scaffold weighing 500 N and supported by vertical ropes at each end. How far would the worker stand from one of the supporting ropes to produce a tension of 770 N in that rope?
a. 1.4 m c. 2.5 m b. 2.0 m d. 2.7 m