In an electric furnace used for refining steel, the temperature is monitored by measuring the radiant power emitted through a small hole in the wall of the furnace, of area 0.5 cm2.
This hole acts like a perfect blackbody radiator having the same temperature as the interior of the furnace. If the temperature of the furnace (and therefore of the hole) is to be maintained at 1650C, how much power will the hole radiate? A) 20 W
B) 30 W
C) 40 W
D) 50 W
Question 2
An ideal parallel-plate capacitor consists of two parallel plates of area A separated by a distance d. This capacitor is connected to a battery and charged until its plates carry charges +Q and -Q, and the battery is then disconnected.
If the separation between the plates is now doubled, the electrical energy stored in the capacitor will A) double.
B) quadruple.
C) be cut in half.
D) be cut in fourth.
E) not change.
This 1900 photograph of steel factories at night in Duquesne, near Pittsburgh, was tinted by hand. S
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