- #1
Myr73
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Homework Statement
A simple type of blinking light circuit can be constructed using a neon lamp. The
circuit shown here has a 4.0 μF capacitor in parallel with a neon lamp. When the
voltage is low in the RC portion of the circuit, the lamp does not conduct
electricity. Therefore, it is
effectively not there from an
electrical point of view. The RC
circuit will then charge from the
110 V power supply. However,
when the voltage across the
capacitor reaches 75 V, the neon
will ionize very quickly and the
neon lamp will become a very
good conductor, and will immediately discharge the capacitor. The energy stored
in the capacitor will be given off as a flash of orange light, making this a useful
circuit. After the flash, the charging process will start once more since the
voltage will again be low.
a. Determine the flash frequency with the resistance value shown.
b. Make a sketch of the voltage across the capacitor versus time in such a
circuit, showing several periods.
C=4X10^-6 ε=110V Vc=75V R= 2.5 X 10-4
Homework Equations
t=1/f T=RC Vc=ε(1-e^t/RC)
The Attempt at a Solution
So for a) I have T=RC= (2.5X10^-4)(4X10^-6)= 0.1s <-- time constant for the circuit
Vc=ε(1-3^t/RC)
In (1-{Vc/ε))=-t/RC
t= -In (1-V{c/ε})(RC)
What I don't understand is how to calculate that