A straight wire lies along the y-axis initially carrying a current of 10 A in the positive y-direction. The current decreases and reverses to 10 A in the negative y-direction, the change in current happening at a uniform rate. In the 1st quadrant a square conducting coil has 2 sides parallel to the y-axis and the other 2 sides parallel to the x-axis. The side of the coil nearest and parallel to
the straight wire is at a distance equal to the length of one of the sides of the square. As the current is going from 10 A in one direction to 10 A in the other, in which direction is the induced current in this side of the square coil nearest to the straight wire?
a. It is in the positive y-direction.
b. It is in the negative y-direction.
c. At first it is in the positive y-direction, but after the current passes through zero, it is in the negative y-direction.
d. At first it is in the negative y-direction but after the current passes through zero, it is in the positive y-direction.
a
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Water at a temperature of 77°C is to be evaporated slowly in a vessel. The water is in a low pressure container surrounded by steam as shown in the sketch below. The steam is condensing at 107°C. The overall heat transfer coefficient between the water and the steam is 1100 W/(m2 K). Calculate the surface area of the container which would be required to evaporate water at a rate of 0.01 kg/s.
GIVEN
• Water evaporated slowly in a low pressure vessel surrounded by steam
• Water temperature (Tw) = 77°C
• Steam condensing temperature (Ts) = 107°C
• Overall transfer coefficient between the water and the steam (U) = 1100 W/(m2 K)
• Evaporation rate m
w= 0.01 kg/s
FIND
• The surface area (A) of the container required
ASSUMPTIONS
• Steady state prevails
• Vessel pressure is held constant at the saturation pressure corresponding to 77°C
SKETCH
PROPERTIES AND CONSTANTS
The heat transfer required to evaporate water at the given rate is q = m
Reasoning from the fact that it is difficult to pull a nucleus apart, we can conclude that the nuclear force must
A) be attractive and very strong. B) have a very short range. C) have a very long range. D) operate only between neutrons, and not between protons. E) be repulsive and very strong.
Which of these following statements about atoms is valid?
1) The atom is the smallest particle that exists. 2) There are thousands of kinds of atoms, accounting for the great variety of substances. 3) There are nearly 100 different kinds of atoms found in nature. 4) Atoms are small building blocks of nature, being so small they cannot be photographed. The word molecule can be at least partly identified by the following statement: 5) The molecule is the smallest particle that exists. 6) The molecule is the smallest subdivision of matter that still retains the chemical properties of the substance from which it originates. 7) Combinations of molecules form atoms. 8) The chemical elements consist of 105 different molecules, a list that keeps growing.
As stars evolve, their temperature and luminosity change; therefore, their spectral type (OBAF, etc.) changes as well.
Answer the following statement true (T) or false (F)