Thin Lenses: Is it possible to see a virtual image?
A. No, since the rays that seem to emanate from a virtual image do not in fact emanate from the image.
B. No, since virtual images do not really exist.
C. Yes because the rays that appear to come from a virtual image can be focused by the eye just like those from an object.
D. Yes, but only by using an additional lens to form a real image before the light reaches the eye.
Answer: C
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A light oil flows through a copper tube of 2.6-cm-ID and 3.2-cm-OD. Air flows perpendicular over the exterior of the tube as shown in the following sketch. The convection heat transfer coefficient for the oil is 120 W/(m2 K) and for the air is 35 W/(m2 K). Calculate the overall heat transfer coefficient based on the outside area of the tube (a) considering the thermal resistance of the tube, (b) neglecting the resistance of the tube.
GIVEN
• Air flow over a copper tube with oil flow within the tube
• Tube diameters
? Inside (Di) = 2.6 cm = 0.026 m
? Outside (Do) = 3.2 cm = 0.032 m
• Convective heat transfer coefficients
? Oil h i= 120 W/(m2 K)
? Air h o= 35 W/(m2 K)
FIND
• The overall heat transfer coefficient based on the outside tube area (Uo), (a) considering the thermal resistance of the tube, and (b) neglecting the tube resistance
ASSUMPTIONS
• Uniform heat transfer coefficients
• Variation of thermal properties is negligible
SKETCH
PROPERTIES AND CONSTANTS
the thermal conductivity of copper (k) = 392 W/(m K) (at 127°C)
Based on what we know about our own solar system, the discovery of hot Jupiters came as a surprise to scientists because these planets are __________.
Fill in the blank(s) with the appropriate word(s).
A substance with a high thermal inertia has a high
A) temperature, in many cases. B) heat conductivity. C) specific heat capacity. D) energy content.
A high f-number:
a. allows using a slower shutter speed. b. causes more spherical aberration. c. allows a larger depth of focus. d. is not related to any of the above options.