Northern hemisphere winters are colder than northern hemisphere summers because
a. Earth is closer to the Sun during the summer than it is during the winter.
b. the snow that falls in the northern latitudes cools Earth during the winter.
c. the light from the Sun shines more directly on the northern hemisphere during the summer.
d. the period of sunlight is longer during the summer than during the winter.
e. the light from the Sun shines more directly on the northern hemisphere during the summer and the period of sunlight is longer during the summer than during the winter.
e
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Imagine that we have two isolated metal spheres. The one on the left has a negative charge, while the one on the right has a positive charge. If these spheres are connected with a straight metal wire, what direction does the conventional current flow?
A. Left to right B. Right to left C. Because there is no electric field, no current flows. D. The direction depends on the spheres’ relative sizes.
The ______ rate is the number of times per second that the picture within the video changes.
A. bit B. frame C. sampling D. screen
What is the relationship between color and wavelength for light?
a. Wavelength increases from blue light to red light b. Wavelength decreases from blue light to red light c. All colors of light have the same wavelength. d. Wavelength depends on intensity not color.
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