Assume you are a particle in a box called the universe. Estimate your minimum kinetic energy. (Assume the "edge" of the box is at a distance of 20. Giga Light Years.)
What will be an ideal response?
6 × 10-123Joules = 3 × 10-104 eV from ?/2 = 2R (R = 20. GLY) and K = p2/(2m) = h2/2m?2)
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Accelerate an electron and you produce an electromagnetic wave. Accelerate a massive body and you produce
A) a gravitational wave. B) a cosmic wave. C) both of these D) neither of these
An electrical transmission line of 1.2 cm diameter carries a current of 200 Amps and has a resistance of 3 × 10–4 ohm per meter of length. If the air around this line is at 16°C, determine the surface temperature on a windy day, assuming a wind blows across the line at 33 km/h.
GIVEN
• An electrical transmission line on a windy day
• Line outside diameter (D) = 12 cm = 0.012 m
• Current (I) = 200b Amps
• Resistance per unit length (Re/L) = 3 × 10–4 ohm/m
• Air temperature (Tb) = 16°C
• Air velocity (V) = 33 km/h = 9.17 m/s
FIND
• The line surface temperature (Ts) ASSUMPTIONS
• Steady state conditions
• Air flow approaching line has low free-stream turbulence
SKETCH
PROPERTIES AND CONSTANTS
Thermal conductivity (k) = 0.0248 W/(m K) Kinematic viscosity (?) = 15.3 × 10–6 m2/s Prandtl number (Pr) = 0.71
What is Earth's distance from the Sun?
a. 0.39 AU b. 0.72 AU c. 1.0 AU d. 1.5 AU e. 2.8 AU
What happens to energy in the Sun's convection zone?
A) Energy is produced in the convection zone by thermal radiation. B) Energy is transported outward by the rising of hot plasma and sinking of cooler plasma. C) Energy slowly leaks outward through the radiative diffusion of photons that repeatedly bounce off ions and electrons. D) Energy is produced in the convection zone by nuclear fusion.