Galaxy A and galaxy B formed at the same time. Galaxy A is much farther from us than galaxy B. Which of the following is true?
A) Galaxy A will appear younger to us than galaxy B.
B) Galaxy A will appear older to us than galaxy B.
C) Galaxy A will appear to be the same age as galaxy B.
A) Galaxy A will appear younger to us than galaxy B.
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Jadeen says that you can increase the resistance of a copper wire by hammering the wire to make it narrower and longer. Arnell says that you can increase its resistance by heating the wire. Which one, if either, is correct, and why?
a. Arnell, because the conductivity of the wire increases when it is heated. b. Arnell, because the conductivity of the wire decreases when it is heated. c. Jadeen, because the conductivity of a wire is directly proportional to its area and inversely proportional to its length. d. Jadeen, because the conductivity of a copper wire does not increase when it is hammered. e. Both are correct because (b) and (d) are both correct.
Impulse involves the time that a force acts, whereas work involves the
A) distance that a force acts. B) time and distance that a force acts. C) acceleration that a force produces.
A long straight wire (diameter = 2.0 mm) carries a current of 25 A. What is the magnitude of the magnetic field 0.50 mm from the axis of the wire?
a. 5.0 mT b. 10 mT c. 0.63 mT d. 2.5 mT e. 0.01 mT
Experiments have been performed on the temperature distribution in a homogeneous long cylinder (0.1 m diameter, thermal conductivity of 0.2 W/(m K) with uniform internal heat generation. By dimensional analysis, determine the relation between the steady-state temperature at the center of the cylinder Tc the diameter, the thermal conductivity, and the rate of heat generation. Take the temperature at the surface as you datum. What is the equation for the center temperature if the difference between center and surface temperature is 30°C when the heat generation is 3000 W/m3?
GIVEN
A homogeneous long cylinder with uniform internal heat generation
Diameter (D) = 0.1 m
Thermal conductivity (k) = 0.2 W/(m K)
Difference between surface and center temperature (Tc – Ts) = 30°C
Heat generation rate q = 3000 W/m3
FIND
(a) Relation between center temperature (Tc), diameter (D), thermal conductivity (k), and rate of heat
generation q
(b) Equation for the center temperature for the given data
ASSUMPTIONS
Steady state
One dimensional conduction in the radial direction
SKETCH
