1
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 by 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 by 4 by 2 cubic meters).
2
Grains of pollen of mass M are entrained (carried along) 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 cm and the depth of the cell is 8 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 you can find out what M really is).
3
Sparks and discharges (as seen in "Jacob's ladder") emit bluish light. What are the frequency and wavelength of this light? What is the energy of an emitted photon, in eV? You can give a range of values or a typical value.
4
A steel wire of radius a hangs at the center of a steel pipe of radius b. If the wire is at potential V and the pipe is grounded, what is the field at the surface of the wire? I am asking for an exact answer in the idealized case of wire and pipe of infinite length. Assuming that the radius of the pipe is 5 cm, what practically feasible a and V will give a good corona discharge? You can just give typical values.