Why are leaves green and not yellow, for example? Explain
What will be an ideal response?
The short answer is that the green light in the spectrum is reflected from leaves
while the blue and red are absorbed.
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Ptolemy formulated a(n) ____________________ model of the solar system to predict positions of the Sun, Moon, and planets
Fill in the blank(s) with correct word
A blacksmith is flattening a steel plate that measures 10 cm × 15 cm × 1 mm. He has heated the plate to 900 K. If the emissivity of the plate is 0.75, what is the total rate at which it radiates energy?
The Stefan-Boltzmann constant is 5.670 × 10-8 W/m2 • K4. Ignore any heat it receives from the surroundings. A) 880 W B) 790 W C) 760 W D) 850 W E) 360 W
The width of a nuclear state is found to be 10-2 eV. The corresponding lifetime of this state is
A) 10-36 s. B) 10-2 s. C) 10-4 s. D) 4 × 10-13 s. E) 7 × 10-14 s.
It has been proposed that highly concentrating solar power such as the one below can be used to process materials economically when it is desirable to heat the material surface rapidly without significantly heating the bulk. In one such process for case hardening low-cost carbon steel, the surface of a thin disk is to be exposed to concentrated solar flux.
The distribution of absorbed solar flux on the disk is given by
where r is the distance from the disk axis and q''max and Ro are parameters that describe
the flux distribution. The disk diameter is 2Rs, its thickness is Zs, its thermal conductivity
is k and its thermal diffusivity is a. The disk is initially at temperature Tinit and at time
t = 0 it is suddenly exposed to the concentrated flux. Derive the set of explicit difference
equations needed to predict how the disk temperature distribution evolves with time. The
edge and bottom surface of the disk are insulated and reradiation from the disk is
neglected.
GIVEN
- Steel disk exposed to concentrated solar flux
FIND
(a) Explicit difference equations that describe evolution of disk temperature