The Bohr model pictures a hydrogen atom in its ground state as a proton and an electron separated by the distance a0 = 0.529 × 10?10 m. The electric potential created by the proton at the position of the electron is
A. ?13.6 V.
B. +13.6 V.
C. ?27.2 V.
D. +27.2 V.
E. +5.12 × 109 V.
Answer: D
You might also like to view...
A shell-and-tube heat exchanger is to be used to cool 25.2 kg/s of water from 38°C to 32°C. The exchanger has one shell-side pass and two tube side passes. The hot water flows through the tubes and the cooling water flows through the shell. The cooling water enters at 24°C and leaves at 32°C. The shell-side (outside) heat transfer coefficient is estimated to be 5678W/(m 2 K). Design specifications require that the pressure drop through the tubes be as close to 13.8 kPa as possible and that the tubes be 18 BWG copper tubing (1.24 mm wall thickness), and each pass is 4.9 m long. Assume that the pressure losses at the inlet and outlet are equal to one and one half of a velocity heat (?V2/gc), respectively. For these specifications, what tube diameter and how many tubes are needed?
GIVEN
A water-to-water shell-and-tube exchanger, hot water in tubes, cooling water in shell One shell and two tube passes Hot water flow rate m
h= 25.2 kg/s Water temperatures
? Hot: Th,in = 38°C Th,out = 32°C
? Cold: Tc,in = 24°C Tc,out = 32°C Shell-side transfer coefficient h o= 5678 W/(m2 K) Pressure drop (?p) = 13.8 kPa Tube wall thickness (t) = 1.24 mm = 0.00124 m Tube length per pass (Lp) = 4.9 m
FIND
The tube diameter (Do) and number of tubes (N)
ASSUMPTIONS
Pressure losses at inlet and outlet (?pii) = 1.5 (? V2/gc) Variation of thermal properties with temperature is negligible Fouling resistance is negligible Thermal resistance of the tube walls is negligible
SKETCH
PROPERTIES AND CONSTANTS
for water at 30°C Density (?) = 995.7 kg/m3
Specific heat (cp) = 4176 J/(kg K)
Thermal conductivity (k) = 0.615 W/(m K)
Kinematic viscosity (?) = 0.805 × 10–6 m2/s
Prandtl number (Pr) = 5.4
Which of the following best describes Fermi's Paradox?
A) Galactic civilizations seem forbidden by the laws of physics. B) Interstellar travel is possible yet would take an infinite amount of time because of relativistic time dilation. C) We would be unable to detect an Earthlike planet even at a distance of a few light-years. D) Reasonable assumptions predict that a galactic civilization should have already arisen in the Milky Way, yet we have absolutely no evidence for it. E) The Drake equation predicts that there should be no intelligent life in the Milky Way, yet we exist.
In order to find the depth of a well, you drop a stone into it and time its fall. It hits the water after falling for 1.5 s. The depth of the well is about
A. 20 m. B. 11 m. C. 14 m. D. 7.35 m.
According to the equipartition theorem, the molar heat capacity of a monatomic ideal gas