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%TCIDATA{Created=Tue Jul 02 15:53:04 1996}
%TCIDATA{LastRevised=Thu Jan 23 11:45:48 1997}
%TCIDATA{Language=American English}

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Phys 312

{\bf Assignment 2, due 30 Jan 97}
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{\bf 1}

\noindent In a desktop electrostatic air cleaner, air is driven through the
``cell'' by a fan that draws 55 W (when set at ``high''). The cross
sectional dimensions of the cell are $25\,$cm $\times \,5\,$cm. Neglecting
losses, you can compute the speed of air flow, $v,$ from these data. Compare
this computed value of $v$ with the value ``measured'' in class. (At the
calculated $v$) how many minutes does it take to process a volume of air
equal to that of a typical room? (Take the room to be $4$ $\times \,4$ $\times
\,2$ cubic meters).

\smallskip 

{\bf 2}

\noindent Grains of pollen of mass $M$  are entrained by air moving at speed 
$v$ (as calculated in problem 1) between plates held at a potential
difference $V=5500\,$Volts. The distance between plates is 0.6\thinspace cm
and the depth of the cell is 8\thinspace cm. Will the pollen be collected
for sure on the positive plate when a grain picks up the elementary charge $e
$ or does it have to be multiply charged? I am particularly concerned with
oak pollen that has very small grains, only 10 micrometers in
diameter (you can you estimate $M$ from this or maybe you can find out what $%
M$ really is).

\smallskip 

{\bf 3}

\noindent Light is emitted in a transition from a state of energy
-7.5\thinspace eV to a state of energy - 8.4\thinspace eV. What is the
frequency? What is the wavelength? Is it visible light and if so what is its
color?

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