Fresnel lenses are
a. made of mirror segments.
b. made of the surface portions of a regular lens.
c. found in some auto headlamps and theater lights and rear windows of RVs.
d. all of the above.
b, c
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Ball bearings are to be hardened by quenching them in a water bath at a temperature of 37°C. You are asked to devise a continuous process in which the balls roll from a soaking oven at a uniform temperature of 870°C into the water, where they are carried away by a rubber conveyer belt. The rubber conveyor belt, however, is not satisfactory if the surface temperature of the balls leaving the water is above 90°C. If the surface coefficient of heat transfer between the balls and the water may be assumed to be equal to 590 W/(m2 K), (a) find an approximate relation giving the minimum allowable cooling time in the water as a function of the ball radius for balls up to 1.0-cm in diameter, (b) calculate the cooling time, in seconds, required for a ball having a 2.5- cm-diameter, and (c)
calculate the total amount of heat in watts which has to be removed from the water bath in order to maintain a uniform temperature if 100,000 balls of 2.5-cm-diameter are to be quenched per hour.
GIVEN
FIND
(a) An approximate relation giving the minimum allowable cooling time in the water as a function of the ball
radius for balls upto 1.0 cm in diameter
(b) The cooling time, in seconds, required for a ball having a 2.5-cm-diameter
(c) The total amount of heat in watts which would have to be removed from the water bath in order to
maintain its temperature uniform if 100,000 balls of 2.5 cm diameter are to be quenched per hour
ASSUMPTIONS
The ball bearings are 1% carbon steel
SKETCH
Which of the following is true of Phobos?
A) It is bigger than Mars. B) It is almost certainly a captured asteroid. C) Its gravitational acceleration is equivalent to that of Earth. D) Its atmosphere is completely made of nitrogen.
The relative brightness of the stars as we see them in our sky is represented by their
A. luminosity. B. absolute magnitude. C. apparent magnitude. D. surface temperature.
Spherical Mirrors: A stature that is 3.0 cm tall statue is 24 cm in front of a concave mirror. The magnitude of the radius of curvature of the mirror is 20 cm.(a) Is the image real or virtual?(b) How far is the image from the mirror?(c) Is the image upright or inverted?(d) How tall is the image?
What will be an ideal response?