Most telephone cables are made of copper wire of either 24 or 26 gauge. If the resistance of 24-gauge wire is 137 ?/mile and the resistance of 26-gauge wire is 220 ?/mile, what is the ratio of the diameter of 24-gauge wire to that of 26-gauge wire?
a. 1.6
b. 1.3
c. 0.62
d. 0.79
e. 0.88
b
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Redshift surveys give us
A) a 3-D layout of galaxies in space. B) a better value of the speed of light. C) an idea of how turbulent the intergalactic gas is. D) the total mass of the universe. E) a more accurate census of the Local Group.
Diffraction Gratings: An 18-mm-wide diffraction grating has rulings of 710 lines per millimieter. Monochromatic light of wavelength 506 nm wavelength is incident normally on the grating. What is the largest angle from the centerline at which an intensity maximum is formed?
A. 46° B. 44° C. 42° D. 40° E. 38°
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
Resistance and Resistivity: The resistance of a 100-cm wire of cross sectional area 2 × 10-6 m2 is 400 ?. What is the resistivity of the material from which this wire is made?
A. 0.80 × 10-4 ? ? m B. 8.0 × 10-4 ? ? m C. 0.80 × 10-5 ? ? m D. 0.80 × 10-6 ? ? m E. 8.0 × 10-6 ?v