What causes thunder?
1 answer:
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The correct answer is
b. low frequencies and low energy.
In fact, microwaves and radio waves have frequency up to , which are really low compared, for instance, to the frequency of gamma rays (
). Moreover, the energy of an electromagnetic wave is directly proportional to its frequency:
where h is the Planck constant and f the frequency; therefore, low frequency means also low energy.
Answer:
<em>1.01 W/m</em>
Explanation:
diameter of the pipe d = 30 mm = 0.03 m
radius of the pipe r = d/2 = 0.015 m
external air temperature Ta = 20 °C
temperature of pipe wall Tw = 150 °C
convection coefficient at outer tube surface h = 11 W/m^2-K
From the above,<em> we assumed that the pipe wall and the oil are in thermal equilibrium</em>.
area of the pipe per unit length A = =
m^2/m
convectional heat loss Q = Ah(Tw - Ta)
Q = 7.069 x 10^-4 x 11 x (150 - 20)
Q = 7.069 x 10^-4 x 11 x 130 = <em>1.01 W/m</em>