Cal is viewing the Moon with his new telescope, using a 10-mm focal length eyepiece. For greater detail, he wishes to double the magnification of his telescope
An eyepiece having which one of the following characteristics will accomplish this for him? A) 40 diopters
B) 8 mm
C) 12 mm
D) 200 diopters
E) 5 diopters
D
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Assume that the water is originally at the freezing temperature Tf, that the cooling medium inside the tube surface is just below the freezing temperature at a uniform temperature Ts, and that ho is the total heat transfer coefficient between the cooling medium and the pipe-ice interface. Also show the thermal circuit.
Show that the dimensionless equation for ice formation at the outside of a tube of radius ro is
where
GIVEN
? Water freezing on the outside of a tube
? Tube radius = ro
? Cooling medium temperature = T ? (uniform)
? Heat transfer coefficient between the cooling medium and the pipe-ice interface = ho
FIND
? Draw the thermal circuit and show that the dimensionless equation for ice formation is as shown
above
ASSUMPTIONS
? Steady state
? The thermal capacitance of the ice layer is negligible
? T? is constant
? The water is at the freezing temperature, Tf
? The properties of the ice are uniform
SKETCH
What makes the North Star, Polaris special?
a) it appears very near the north celestial pole b)it is the brightest star in the sky c) it can be used to determine your longitude on Earth d) it is the star directly on your northern horizon
The nichrome heating element in an electric drier operates on 240 V and generates heat at the rate of 2.0 kW
The heating element shorts out and, in repairing it, the repairman shortens the nichrome wire by 10%. (Assume the temperature is unchanged. In reality, the resistivity of the wire will depend on its temperature.) What effect will the repair have on the power dissipated in the heating element? A) The power increases to 2.2 kW. B) The power is still 2.0 kW. C) The power decreases to 1.8 kW. D) None of the given answers is correct.
A metallic key ring of 1.00 cm diameter is placed in a fire and heated up. What would you expect would happen to the inside diameter of the ring as it heats up?
1.It will shrink as the metallic portion expands. 2.It will expand as the metallic portion expands. 3.It will stay the same size as the metallic portion expands. 4.It is impossible to say what will happen to the open area in the center of the ring.