Phy 133 - Assignment 6
A. 1. The blue ones. A star is similar to a blackbody, so Wein’s displacement law
applies. It says that T is proportional to 1/max.  for blue is less than  for red.
2.
B. 2. The 3He. Being faster, it spends less time in the barrier. By
, the
uncertainty in its energy is more, meaning E is more likely to fluctuate past 5 MeV.
2.
C.
D.
E. 1. For everyday objects like baseballs, the wavelength is extremely small. ( =
h/(mv), and m is huge compared to an electron.) Wave properties, such as diffraction,
depend on , and so are far too small to measure.
2.
. So,  =
F. a) Combining E = hf and f = c/, E =
When in doubt, work in standard SI units. (joules in this case.) But if you notice
that eV drops out, you can get away with doing it this way:
=
(
)
= 1.216 x 10-7 m = 122 nm
b)
ΔE( 1 x 10-8 s) > (6.58 x 10-16 eV·s)/2
ΔE >
3.29 x 10-8 eV
c)  = hc(E)-1
d = - hc(E)-2dE
Since this is being used as a , the – sign just turns it into . In other words, the
minus doesn’t matter.
d =
=
=
(
)(
)
= 3.92 x 10-16 m
3.29 x 10-7 nm
“Width” would mean from one side of the line to the other.
center to either side. So, multiply by 2.
would be from the
7.84 x 10-7 nm
(I did that to three digits because that’s what we always do, but it’s a ridiculous abuse
of significant figures. In the first place, 1 x 10-8 s is an approximate, one sig fig
number. Also, the line’s width isn’t sharply defined; it fades out at the edges.)