Question

Question 1: Suppose an emergency light has a resistance of 1000 Ω and you wish the...

Question 1:
Suppose an emergency light has a resistance of 1000 Ω and you wish the emergency exit to remain illuminated for 10 minutes after a power failure. How large a capacitor would you need? Show your reasoning and calculations for full credit.

Question 2:
An RC circuit is comprised of 10 µF capacitor, a voltmeter with an internal resistance of 10 MΩ and a battery which may supply 12 V. After fully charging the capacitor, it is allowed to discharge across the resistor. What will be the voltage reading across the resistor 35 seconds after the discharge begins?

Homework Answers

Answer #1

(a) In usual cases we consider 5 times the time constant of a RC circuit to to the effective time at which the capacitor is considered to be fully discharged.

Given time = 10 mins or 600 s

Therefore

(b)

Time constant of given circuit

Given that max voltage is 12 V

therefore

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