An auditorium has dimensions 10 m × 10^ m × 60 m. How many moles of air fill this volume at one atmosphere and 0°C?
a. 2.7 × 10^2
b. 2.7 × 10^4
c. 2.7 × 10^3
d. 2.7 × 10^5
e. 2.7 × 10^6
d
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What actually "controls" Saturn's rings?
a. Saturn's magnetic field b. Saturn's tidal heating c. Saturn's moons d. Saturn's rapid rotation e. Saturn's metallic core
Parallel Wires: Two long parallel wires are placed side-by-side on a horizontal table and carry current in the same direction. The current in one wire is 20 A, and the current in the other wire is 5 A. If the magnetic force on the 20-A wire has magnitude F, what is the magnitude of the magnetic force on the 5-A wire? No external magnetic fields are present.
A. 4F B. 2F C. F D. F/2 E. F/4
A heat exchanger wall consists of a copper plate 2 cm thick. The heat transfer coefficients on the two sides of the plate are 2700 and 7000 W/( m2 K), corresponding to fluid temperatures of 92 and 32°C, respectively. Assuming that the thermal conductivity of the wall is 375 W/ ( m K), (a) compute the surface temperatures in °C, and (b) calculate the heat flux in W/ m2.
GIVEN
• Heat exchanger wall, thickness (L) = 2 cm = 0.02 m
• Heat transfer coefficients
? hc1 = 2700 W/(m2 K)
? hc2 = 7000 W/(m2 K)
• Fluid temperatures
? Tf1 = 92°C
? Tf2 = 32°C
• Thermal conductivity of the wall (k) = 375 W/( m K) FIND (a) Surface temperatures (Tw1, Tw1) in °F (b) The heat flux (q/A) in W/m2. ASSUMPTIONS
• One dimensional heat transfer prevails
• The system has reached steady state
• Radiative heat transfer is negligible
SKETCH
Suppose an object is placed 6.0 cm in front of a lens that has a focal length of 4.0 cm. Where is the image located? What are the magnification and the character of the image?