Changing the f-number of a camera by three stops by going from f/11 to f/32 will change the intensity of the light hitting the film by a factor of
a. 8.
b. 4.
c. 1/4.
d. 1/8.
e. 32.
d
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The fate or future of the universe depends only on the total number of galaxies and quasars
Indicate whether the statement is true or false
Rubber rods charged by rubbing with cat fur repel each other. Glass rods charged by rubbing with silk repel each other. A rubber rod and a glass rod charged respectively as above attract each other. A possible explanation is that
A. any two rubber rods charged this way have opposite charges on them. B. any two glass rods charged this way have opposite charges on them. C. a rubber rod and a glass rod charged this way have opposite charges on them. D. all rubber rods always have an excess of positive charge on them. E. all glass rods always have an excess of negative charge on them.
A steam pipe 200-mm in diameter passes through a large basement room. The temperature of the pipe wall is 500°C, while that of the ambient air in the room is 20°C. Determine the heat transfer rate by convection and radiation per unit length of steam pipe if the emissivity of the pipe surface is 0.8 and the natural convection heat transfer coefficient has been determined to be 10 W/(m2 K).
GIVEN
FIND
- Heat transfer rate by convection and radiation per unit length of the steam pipe (q/L)
ASSUMPTIONS
- Steady state prevails
- The walls of the room are at the same temperature as the air in the room
- 
ASSUMPTIONS
- Steady state prevails
- The walls of the room are at the same temperature as the air in the room
- 
SKETCH
If the magnitude difference between one star and another is 8, the stars differ in brightness by a factor of
a. 2.51. b. 20. c. 7. d. 1580.