The eye focuses by
A. moving the lens.
B. moving the retina.
C. moving both the lens and the retina.
D. changing the focal length of the lens.
E. changing the index of refraction of the vitreous fluid.
D. changing the focal length of the lens.
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Stars with masses between 0.4 and 4
a. undergo thermonuclear fusion of hydrogen and helium, but never get hot enough to ignite carbon. b. undergo thermonuclear fusion of hydrogen, but never get hot enough to ignite helium. c. produce type-I supernovae after they exhaust their nuclear fuels. d. produce type-II supernovae after they exhaust their nuclear fuels. e. undergo carbon detonation.
Single-Slit Diffraction: If a sheet containing a single slit is heated (without damaging it) and therefore expands, what happens to the angular location of the first-order diffraction minimum?
A. It moves toward the centerline. B. It moves away from the centerline. C. It doesn't change.
A radiometer has two square vanes (1.0 cm by 1.0 cm), attached to a light horizontal cross arm, and pivoted about a vertical axis through the center, as shown in the figure
The center of each vane is 6.0 cm from the axis. One vane is silvered and it reflects all radiant energy incident upon it. The other vane is blackened and it absorbs all incident radiant energy. An electromagnetic wave with an intensity of 0.30 kW/m2 is incident normally upon the vanes. What is the torque due to radiation pressure on the vane assembly about the vertical axis? (c = 3.00 × 108 m/s, ?0 = 4? × 10-7 T ? m/A, ?0 = 8.85 × 10-12 C2/N ? m2) A) 2.4 × 10-12 N ? m B) 6.0 × 10-12 N ? m C) 1.2 × 10-11 N ? m D) 1.8 × 10-11 N ? m E) 2.4 × 10-11 N ? m
A metal plate is placed in the sunlight. The incident radiant energy G is 780 W/m2. The air and the surroundings are at 10°C. The heat transfer coefficient by natural convection from the upper surface of the plate is 17 W/(m2 K). The plate has an average emissivity of 0.9 at solar wavelengths and 0.1 at long wavelengths. Neglecting conduction losses on the lower surface, determine the equilibrium temperature of the plate.
GIVEN
- A metal plate is sunlight
- Incident radiant energy
- Temperature of air and surroundings
- Natural convection heat transfer coefficient
- Plate emissivity (?) = 0.9 at solar wavelengths, 0.1 at long wavelengths
FIND
-The equilibrium temperature of the plate (Tp)
ASSUMPTIONS
- Steady state
- Conduction losses on the lower surface of the plate are negligible
- The surroundings behave as a blackbody enclosure
SKETCH
PROPERTIES AND CONSTANTS
the Stephan-Boltzmann constant
