Capacitors charge and discharge at predictable rates similar to growth and decay curves in other areas of nature such as radioactivity or populations.
Lights that turn off automatically, timer circuits, oscillators that drive electronic instruments and wireless transmitters, all use the charging and discharging rates of RC circuits to determine periods of time.
A unit of time called a time constant can
be calculated for and RC circuit that is a circuit with a resisitor and a
capacitor in series.
in the total time (T)
to charge a capacitor through a resistor.
Example : calculate the time required to charge or discharge the following capacitor if the capacitor is
rated at 1000 uF and the resistor 6.7 Kohms.
Tc = RC
= 6700ohms x 0.001F = 6.7s (seconds)
T = 5Tc
= 5(6.7s) = 33.5s
for T time to fully charge
AS R increases T increases (limits rate of electron flow)
AS C increases T increases (takes longer to fill - size counts! -)
and the inverse
LED FLASHER :
C1 the 10 uF cap and R2 the resistor control the flash rate