A conducting sphere of radius 20 cm has a charge Q placed on it producing a field of magnitude
at its surface. More charge is added to the surface until the magnitude of the field at the surface is 2
How much charge was added to the surface?
A. Q/2
B. Q
C. 2 Q
D. 1.4 Q
E. 3 Q
B. Q
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Ohm's Law: The current through a piece of lab equipment must be limited to 2.75 A when it is run by a 120-V dc power supply. What must be the resistance of this equipment?
Fill in the blank(s) with the appropriate word(s).
In a manufacturing process, a fluid is transported through a cellar maintained at a temperature of 300 K. The fluid is contained in a pipe having an external diameter of 0.4 m and whose surface has an emissivity of 0.5. To reduce heat losses, the pipe is surrounded by a thin shielding pipe having an ID of 0.5 m and an emissivity of 0.3. The space between the two pipes is effectively evacuated to minimize heat losses and the inside pipe is at a temperature of 550 K. (a) Estimate the heat loss from the liquid per meter length, (b) If the fluid inside the pipe is an oil flowing at a velocity of 1 m/s, calculate the length of pipe for a temperature drop of 1 K.
GIVEN
- Fluid in concentric pipes, with the space between the pipes evacuated, running through a cellar space
- Cellar temperature (T?) = 300 K
- External diameter of inner pipe (D1) = 0.4 m
- Emissivity of outer pipe surface (?1) = 0.5
- Inside diameter of outer pipe (D2) = 0.5 m
- Emissivity of inner pipe (?2) = 0.3
- Inside pipe temperature (T1) = 550 K
FIND
(a) The heat loss from the liquid per meter length (q/L)
(b) The length of pipe for a temperature drop of 1 K if the fluid is oil flowing at a velocity (V) =1 m/s
ASSUMPTIONS
- Steady state
- Convection between the pipes is negligible
- The thermal resistance of the pipe walls is negligible
- The thickness of the outer pipe wall is negligible (Inside surface area = Outside surface area)
- Area of the cellar is large compared to the pipe so that cellar behaves as a blackbody enclosure at T?
- Oil has the thermal properties of unused engine oil
- The temperature of the inner pipe is constant
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant
for unused engine oil at 550 K
Density (p) = 742 kg/m3
Specific heat (c) 2998 J/(kg K)
On the autumnal equinox the sun is
a. north of the celestial equator. b. south of the celestial equator. c. on the celestial equator and moving north with respect to the equator. d. on the celestial equator and moving south with respect to the equator. e. closest to the north celestial pole.
Solenoid: How many turns should a 10-cm long ideal solenoid have if it is to generate a 1.5-mT magnetic field when 1.0 A of current runs through it? (?0 = 4? × 10-7 T ? m/A)
A. 12 B. 15 C. 120 D. 1200 E. 3200