The figure shows the circuit of a flashing lamp, like those attached to barrels

Question

The figure shows the circuit of a flashing lamp, like those attached to barrels at highway construction sites.  The fluorescent lamp L (of negligible capacitance) is connected in parallel across the capacitor C of a RC circuit.  There is a current through the lamp only when the potential difference across it reaches the breakdown voltage VL ; in this event, the capacitor discharges completely through the lamp and the lamp flashes briefly.  Suppose that two flashes per second are needed.  For a lamp with breakdown voltage VL = 65.0 V, a 95.0 V ideal battery, and a 0.140 ?F capacitor, what should be the resistance R of the resistor?

The figure shows the circuit of a flashing lamp, like those attached to barrels at highway construction sites. The fluorescent lamp L (of negligible capacitance) is connected in parallel across the capacitor C of a RC circuit. There is a current through the lamp only when the potential difference across it reaches the breakdown voltage VL ; in this event, the capacitor discharges completely through the lamp and the lamp flashes briefly. Suppose that two flashes per second are needed. For a lamp with breakdown voltage VL = 65.0 V, a 95.0 V ideal battery, and a 0.140 ?F capacitor, what should be the resistance R of the resistor?

Explanation / Answer

V =65

E= 95

c= 0.14

R = 0.5/( 0.14*10^-6)ln (95/(95-65)

=3098370.8313

=3.0983 m ohm

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