Which is more dangerous, touching a faulty 110-volt light fixture, or a Van de Graaff generator charged to 100,000 volts?
A) touching the light fixture
B) touching the generator
C) touching both are about equally dangerous.
Answer: A
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A string with a mass/length of 0.00200 kg/m is stretched between two points with a tension of 120 N. If the fundamental frequency is 660 Hz, then what is the distance between the two points?
A. 17.5 cm B. 18.6 cm C. 20.3 cm D. 26.7 cm E. 30.0 cm
A solar thermal central receiver generates heat by focusing sunlight with a field of mirrors on a bank of tubes through which a coolant flows. Solar energy absorbed by the tubes is transferred to the coolant which can then deliver useful heat to a load. Consider a receiver fabricated from multiple horizontal tubes in parallel. Each tube is 1-cm-ID and 1-m-long. The coolant is molten salt which enters the tubes at 370°C. Under start-up conditions, the salt flow is 10 gm/s in each tube and the net solar flux absorbed by the tubes is 104 W/m2. The tube wall material will tolerate temperatures up to 600°C. Will the tubes survive start-up? What is the salt outlet temperature?
GIVEN
• Molten salt flowing through a horizontal tube that is absorbing solar energy
• Tube inside diameter (D) = 1 cm = 0.01 m
• Tube length (L) = 1 m
• Entering salt temperature (Tb,in) = 370°C
• Start-up mass flow rate (m) = 10 gm/s = 0.01 kg/s
• Net solar energy absorbed by the tube (qs) = 104 W/m2
• Maximum tube wall temperature (Ts) = 600°C
FIND
(a) Salt outlet temperature (Tb,out)
(b) Will the tubes survive start-up?
SKETCH
PROPERTIES AND CONSTANTS
for molten salt at 370°C
Specific heat (c) = 1629 J/(kg K)
The person who first explained the discrete hydrogen atom spectrum was
a. Max Planck. b. Albert Einstein. c. Neils Bohr. d. Erwin Schrödinger. e. Werner Heisenberg.
Which of the following extrasolar planets would be the most difficult to detect using the Doppler shift method?
A) a low mass planet far from its parent star B) a massive planet close to its parent star C) a low mass planet close to its parent star D) a massive planet far from its parent star