Thin Lenses: A certain slide projector has a lens of focal length 15.0 cm. This lens forms an image measuring 100 cm × 100 cm on the screen when a slide whose dimensions are 50.0 mm × 50.0 mm is being magnified. How far from the lens should the screen be placed?
Fill in the blank(s) with the appropriate word(s).
3.15 m
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A transformer is to be designed to increase the 30 kV-rms output of a generator to the transmission-line voltage of 345 kV-rms. If the primary winding has 80 turns, how many turns must the secondary have?
a. 6 b. 70 c. 920 d. 9200 e. 12
A lens that is thicker at the center than the edges
a. is a converging lens b. is a diverging lens c. always forms a real image d. always forms a virtual image e. none of the above
What is the minimum distance of two points on the moon that can be just resolved by the Keck 10. meter telescope in Hawaii (use a wavelength of 600. nm, lunar distance of 380. thousand Km):
(a) if there were no atmosphere? (b) if the atmosphere limits resolution to 0.2 arc-sec?
A mercury-in-glass thermometer at 40°C (OD = 1 cm) is inserted through duct wall into a 3 m/s air stream at 66°C. This can be modelled as cylinder in cross-flow, as shown in figure. Estimate the heat transfer coefficient between the air and the thermometer.
GIVEN
• Thermometer in an air stream
• Thermometer temperature (Ts) = 40°C
• Thermometer outside diameter (D) = 1 cm = 0.01 m
• Air velocity (V) = 3 m/s
• Air temperature (Tb) = 66°C
FIND
• The heat transfer coefficient ch
ASSUMPTIONS
• Steady state
• Turbulence in the free stream approaching the thermometer is low
• Effect of the duct walls in negligible
SKETCH
PROPERTIES AND CONSTANTS
From Appendix 2, Table 28, for dry air at the bulk temperature of 66°C
Thermal conductivity (k) = 0.0282 W/(m K) Kinematic viscosity (?) = 20*10-6 m2/s Prandtl number (Pr) = 0.71 At the thermometer surface temperature of 40°C, the Prandtl number (Prs) = 0.71