Phy101 GDB IDEA solution June 2012

Phy101 GDB IDEA solution June 2012

"Is there entropy changes associated with the transmission of energy from the sun to the
earth? Are the earth and sun in thermal equilibrium?
Does radiation differ from other modes of heat transfer with respect to the entropy
changes?" Explain your answer with reasoning.
Solution: 1
In the given condition the Sun becomes more entropic while the Earth's biosphere
becomes less entropic. Here the main reason is Earth can become less entropic, which
you may have heard is impossible, is because the Earth is NOT a closed system. It has an
input, the Sun. However, on the other hand the decrease in Earth's entropy is less than the
increase in the Sun's entropy, so overall entropy increases as it always must. So this is
further explanation of my reason
 Solution: 2
Is there entropy changes associated with the transmission of energy from the sun to the
earth?
YES  Entropy = S = integral dQ/T
As Earth has a lower temp, the entropy increase from insolation is lower than the entropy
decrease of the Sun, demonstrating a net increase in entropy.
Another similar note: look at DeltaS on Earth, as sunlight comes and reradiation at night
cools the Earth, and see that that reradiation gives a higher entropy than insolation, so
there is room for us on Earth to create entropy.

PHY 101 4th Assignment idea solution..June 2012

PHY 101 4th Assignment idea solution..
For question no 1 :- Find Angle Refraction ???
look at this formula
Refraction is described by Snell's law, which states that for a given pair of media and a wave with a single frequency, the ratio of the sines of the angle of incidence θ1 and angle of refraction θ2 is equivalent to the ratio of phase velocities (v1 / v2) in the two media, or equivalently, to the opposite ratio of the indices of refraction (n2 / n1):

so from there
sinθ2=n2 (sinθ1/n1)
n1=1.00
there n2=1.52
θ1=30degree

For question no 2 :-
A radio transmitting station operating at a frequency of 120MHz has two identical
antennas that radiate in phase. Antenna B is 9.00m to the right of A. Consider point P
between the antennas and along the line connecting them, a horizontal distance x to the
right of antenna A. For what values of x will constructive interference occur at point P?
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Solution:-

As far i think .... look at this example please.... where the same condition is given.
Two loudspeakers, A and B are driven by the same amplifier and
emit sinusoidal waves in phase. Speaker B is 2.00 m to the right of speaker A.
The frequency of the sound waves produced by the loudspeakers is 206 Hz.
Consider point P between the speakers and along the line connecting them,
a distance x to the right of speaker A. Both speakers emit sound waves
that travel directly from the speaker to point P.
b) For what values of x will constructive interference occur at point P?
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Solution of example:-
Assume speed of sound c = 343 m/s, then wavelength lambda = c/f = 1.665 m and lambda/4 = 0.41626 m. There are two locations between the speakers where there is interference. At the center the path lengths are equal.

For constructive interference you want a pathlength difference equal to lambda multiplied by an integer>=0. Then you have one constructive point at the center and, using similar logic as in A, two more at lambda/2 = 0.83252 m to either side. No more points can fit in that space. The locations are at 1.03 - 0.83252 and 1.03 + 0.83252 m.
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f (frequency) = v (velocity)/ L
v=f*L
L=9.00m
f=120
v=120*(9)=1080