Vision Problems: Mahmood is farsighted and cannot see objects clearly that are closer to his eye than 80.0 cm. What is the focal length of the contact lenses that will enable him to comfortably see objects at a distance of 25.0 cm from his eyes?
A. +36.4 cm
B. -36.4 cm
C. -21.2 cm
D. +21.2 cm
E. +32.5 cm
Answer: A
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A tungsten filament is heated to 2700 K. At what wavelength is the maximum amount of radiation emitted? What fraction of the total energy is in the visible range (0.4 to 0.75 ?m)? Assume that the filament radiates as a gray body.
GIVEN
• Heated tungsten filament
• Filament temperature (Tf) = 2700 K
FIND
(a) Wavelength at which the maximum radiation is emitted (?max)
(b) Percentage of radiation in the visible ranger (0.4 to 0.75 ?m)
ASSUMPTIONS
• The filament radiates as a gray body
SKETCH
A 1500-W heater is connected to a 120-V line. How much heat energy does it produce in 2.0 hours?
A) 1.5 kJ B) 3.0 kJ C) 0.18 MJ D) 11 MJ E) 18 MJ
What is the radius of curvature of the path of a 3.0-keV proton in a perpendicular magnetic field of magnitude 0.80 T?
a. 9.9 mm b. 1.1 cm c. 1.3 cm d. 1.4 cm e. 7.6 mm
In a thermodynamic process, the internal energy of a system in a container with adiabatic walls decreases by 800 J. Which statement is correct?
a. The system lost 800 J by heat transfer to its surroundings. b. The system gained 800 J by heat transfer from its surroundings. c. The system performed 800 J of work on its surroundings. d. The surroundings performed 800 J of work on the system. e. The 800 J of work done by the system was equal to the 800 J of heat transferred to the system from its surroundings.