August 14th, 2011 — capacitors
How many electricians does it take to screw in a light bulb? the answer is two, one to place the light bulb in the socket and other one to rotate the ladder.
How many Lee DeForests does it take to change a light bulb ?
Only one, with plate and grid.
He invented the vacuum tube which is basically a light bulb filament, a screen, and a plate
August 13th, 2011 — capacitors
when the radio is tuned to a station at 570 kHz.
(a) what must be the capacitance for a station at 1600 kHz?
pF
(b) what is the inductance (assumed constant)?
µH
For a resonance circuit,
w^2 = 1/(LC)
where w = 2*pi*f
Substituting C=2700pF and f=570kHz into the equation, you get L=28.88uH.
Substituting L=28.88uH and f=1600kHz into the equation, you get C=342.67pF.
July 13th, 2011 — capacitors
In the electronics texts, current is shown going "through" a capacitor, yet the capacitor has a dielectric which doesn't allow passage of electrons. I know electrons traverse at dielectric breakdown but I don't understand how they traverse when there is no breakdown.
Current does indeed flow into and out of the capacitor, but no current flows through it. let me explain:
Current flows into one plate of the capacitor, which is the same as saying electrons flow out (because of the silly convention). this causes that plate to acquire a positive charge.
Current flows out of the other plate, so electrons are flowing in. this means that plate acquires a negative charge.
Eventually the build-up of charge on the two plates prevents any more current flowing.
Another way of looking at it is that electrons do travel from one plate to another, but they take the long way round — around the circuit — rather than through the dielectric.
Dc can not pass thru a capacitor. Signals such as audio and RF can. they pass thru because the oscillation in the applied voltage causes a corresponding oscillation on the other plate as electrons are alternately attracted and repelled by the changing charge applied on the incoming side. Higher value (in uf) capacitors pass low frequencies better, and lo value (usually in pf) pass higher frequencies.
They do not pass through as Charles explained.
Only the variations are conducted.
The electrons accumulate on the plates. if the voltage gets high enough then it will break down.
I hope this answers your question
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