Intensity: The rate of energy flow per unit area of a sinusoidal electromagnetic wave has an average value of 0.601 W/m2. What is the maximum value of the magnetic field in the wave? (c = 3.00 × 108 m/s, ?0 = 4? × 10-7 T ? m/A, ?0 = 8.85 × 10-12 C2/N ? m2)
A. 7.09 × 10-8 T
B. 5.02 × 10-8 T
C. 3.55 × 10-8 T
D. 9.81 × 10-8 T
E. 1.42 × 10-7 T
Answer: A
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The total mechanical energy of a system
A) is equally divided between kinetic energy and potential energy. B) is either all kinetic energy or all potential energy, at any one instant. C) can never be negative. D) is constant, if only conservative forces act. E) is not uniquely determined for most naturally occurring systems.
On the main sequence, almost all stars have radii between about 0.1 and 10 times the Sun
Indicate whether the statement is true or false
Projectile Motion: An athlete competing in the long jump leaves the ground with a speed of 9.14 m/s at an angle of 35° above the horizontal. How long does the athlete stay in the air, assuming no significant air resistance?
A. 0.50 s B. 0.88 s C. 1.1 s D. 2.5 s E. 0.54 s
A spherical vessel 0.3-m in diameter is located in a large room whose walls are at 27°C (see sketch). If the vessel is used to store liquid oxygen at –183°C and both the surface of the storage vessel and the walls of the room are black, calculate the rate of heat transfer by radiation to the liquid oxygen in watts and in Btu/h.
GIVEN
• A black spherical vessel of liquid oxygen in a large black room
• Liquid oxygen temperature (To) = –183°C = 90 K
• Sphere diameter (D) = 0.3 m
• Room wall temperature (Tw) = 27°C = 300 K
FIND
• The rate of radiative heat transfer to the liquid oxygen in W and Btu/h
ASSUMPTIONS
• Steady state prevails
• The temperature of the vessel wall is the same as the temperature of the oxygen
SKETCH
PROPERTIES AND CONSTANTS
The Stefan-Boltzmann constant (?) = 5.67 ? 10–8 W/(m2 K4)