The electric flux through the two adjacent spherical surfaces shown below is known to be the same
It is also known that there is no charge inside either spherical surface. We can conclude that
a.
there is no electric field present in this region of space.
b.
there is a constant E field present in this region of space.
c.
the electric flux has a constant value of zero.
d.
any of the above may be correct.
e.
only (a) and (b) above may be correct.
d
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Ultramafic rocks are commonly found forming at the Earth's surface.
Indicate whether the statement is true or false.
A 2.5-cm-diameter cylindrical refractory crucible for melting lead is to be built for thermocouple calibration. An electrical heater immersed in the metal is shut off at some temperature above the melting point. The fusion-cooling curve is obtained by observing the thermocouple emf as a function of time. Neglecting heat losses through the wall of the crucible, estimate the cooling rate (W) for the molten lead surface (melting point 327.3°C, surface emissivity 0.8) if the crucible depth above the lead surface is (a) 2.5 cm, (b) 17 cm. Assume that the emissivity of the refractory surface is unity and the surroundings are at 21°C, (c) Noting that the crucible would hold about 0.09 kg of lead for which the heat of fusion is 23,260 J/kg, comment on the suitability of the crucible for the
purpose intended.
GIVEN
A cylindrical refractory crucible filled with molten lead
Cylinder diameter (D) = 2.5 cm
Melting point of lead (T1) = 327.2°C = 600.3 K
Surface emissivity of lead (?1) = 0.8
Mass of lead in crucible (m) = 0.09
Heat of fusion of lead (hfg) = 23,260 J/kg
FIND
The cooling rate (q) if the crucible depth above the lead surface (L) is
(a) 2.5 cm = 0.025 m
(b) 17 cm = 0.17 m
(c) Comment on the suitability of the crucible for thermocouple calibration
ASSUMPTIONS
Heat loss through the wall of the crucible is negligible
The emissivity of the refractory surface (crucible wall above the lead) is unity (?2 =1)
The surroundings behave as a blackbody enclosure
The temperature of the refractory surface is uniform at TR
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant
for air at the film temperature of
Thermal expansion coefficient
Thermal conductivity
Kinematic viscosity
Prandtl number (Pr) = 0.71
A 5.00 kg mass is located at (2.00 m, 0.00 m, 3.00 m) and a 2.00 kg mass is located at (0.00 m, 4.00 m, –2.00 m). The center of gravity of the system of masses is
A. (10/7m, 8/7m, 11/7m). B. (11/7m, 7/7m, 8/7m). C. (7/7m, 10/7m, 11/7m). D. (10/7m, 7/7m, 8/7m). E. (8/7m, 7/7m, 10/7m).
An image is 4.0 mm in front of a convex lens with focal length of magnitude 5.0 mm. Where is the object for this image?
A) 2.2 mm in front of the lens B) 2.2 mm behind the lens C) 9.0 mm behind the lens D) 20 mm in front of the lens