I have connected an Incandescent light bulb (R1) in series with a capacitor (C1) to the power line like so:
With the capacitors I have, only for capacitor values C1 = 17uF, 20uF and 22uF does the bulb glow.
For capacitor values C1 = 1uF, 2uF and 2.2uF the bulb does not glow.
The cold resistance of the bulb is 19 Ohms.
When the bulb glows, I got the following readings from my Kill-a-watt:
- Current draw: 0.45A
- Voltage: 117.4vac
- PF: 0.91
- Wattage: 48W (52VA)
From wikipedia, I read the cold resistance of tungsten-filament lamps is about 1/15 the hot-filament resistance when the lamp is operating
This agrees with the readings on the Kill-a-watt as the current through the circuit would be 0.45A if the resistance of the bulb was indeed 15 times the cold resistance (19 * 15 = 285 Ohms. Hence, 117.4/285 = 0.41A).
What I don't understand is why the bulb lights for capacitor values 17uF, 20uF and 22uF but not for 1uF, 2uF and 2.2uF.
With resistor value of 19 Ohms, capacitor values 17uF, 20uF and 22uF should have a cut off freq of more than a few Khz, hence not letting the 60Hz AC through?
Why I say a cut off freq of more than a few Khz:
Because T = RC, and here if R = 100Ohm, C = 20uF, then RC = 100 * (20 / 10^6) => f = 1/T = 500Hz which is much more than 60Hz AC and hence no signal should be out.
(Of course, my understanding wrong as I can see light on, but I want understand where I am wrong.)
Does it imply the higher value caps I am using are damaged (although they read the correct values)?