(8c27p66) The figure shows the circuit of a flashing lamp, like those attached t

Question

(8c27p66) 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 V 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 63.0 V, a 95.0 V ideal battery, and a 0.160 HF capacitor, what should be the resistance R of the resistor? Subml AnsrTries 0/10

Explanation / Answer

t = 1/2 = 0.5 s

VL = VC = E (1 - e-t/RC)

VL / E = (1 - e-t/RC)

R = t / [C * ln (E / E - VL)]

= 0.5 / [0.160 * 10-6 * ln (95 / 95 - 63)]

resistance R = 2.87 * 106 ohms

R = 2.87 M.ohms

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