A uniform 4.5-T magnetic field passes through the plane of a wire loop 0.20 m2 in area. What flux passes through the loop when the direction of the 4.5-T field is at a 30° angle to the normal of the loop plane?
a. 0.39 T×m2
c. 0.78 T×m2
b. 5.0 T×m2
d. 0.225 T×m2
C
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There is a legend of a Dutch boy who bravely held back the Atlantic Ocean by plugging a leak near the top of a dike with his finger until help arrived. Which is the more likely scenario?
A) the huge size of the Atlantic Ocean makes this impossible B) although the force on his finger would have been huge, the pressure would have been small enough for this to occur C) the force on his finger would have been less than 1 N D) both force and pressure on his finger would have been great, but not too great for a public-spirited Dutch lad E) none of the above
A 1200 W hair dryer used for 10 minutes uses as much energy as a 1000 W hair dryer run 12 minutes
What will be an ideal response?
The heat transfer coefficients for the flow of 26.6°C air over a 1.25 cm diameter sphere are measured by observing the temperature-time history of a copper ball of the same dimension. The temperature of the copper ball (c = 376 J/(kg K), ? = 8928 kg/m3) was measured by two thermocouples, one located in the center, and the other near the surface. The two thermocouples registered, within the accuracy of the recording instruments, the same temperature at any given instant. In one test run, the initial temperature of the ball was 66°C and the temperature decreased by 7°C in 1.15 min. Calculate the heat transfer coefficient for this case.
IVEN
• A copper ball with air flowing over it
• Ball diameter (D) = 1.25 cm = 0.0125 m
• Air temperature (T?) = 26.6°C
• Specific heat of ball (c) = 376 J/(kg K)
• Density of the ball (P) = 8928 kg/m3
• Thermocouples in the center and the surface registered the same temperature
• Initial temperature of the ball (To) = 66°C
• Lapse time = 1.15 min = 69 s
• The temperature decrease (To – Tf) = 7°C
FIND
• The heat transfer coefficient ch
ASSUMPTIONS
• The heat transfer coefficient remains constant during the cooling period.
SKETCH
Which hypothetical universe will eventually contract, if there were no dark energy?
A) the universe with 1.5 times the critical density of matter B) the universe with 1.0 times the critical density of matter C) the universe with 0.5 times the critical density of matter