Just need some explanation of the right answer: An initially uncharged capacitor

Question

Just need some explanation of the right answer: An initially uncharged capacitor is being charged through aresistor by a seat of emf. At the end of one time constant thevoltage across the resistor is 3.0 V. At the end of two timeconstants the voltage across the resistor will be? Student Response Value Correct Answer Feedback A. 1.1 V 1.5 V 0% C. 4.5 V D. 6.0 V E. 9.0 V Score: 0/1
The correct answer is A. 1.1V Please explain how to obtain..thanks. An initially uncharged capacitor is being charged through aresistor by a seat of emf. At the end of one time constant thevoltage across the resistor is 3.0 V. At the end of two timeconstants the voltage across the resistor will be? Student Response Value Correct Answer Feedback A. 1.1 V B. 1.5 V 0% C. 4.5 V D. 6.0 V E. 9.0 V Score: 0/1

Explanation / Answer

Voltage after time t is V = Vo e -t / T where T = time constant at t= T , V = 3 Volts plug it in above we get 3 = Vo e-1                                  Vo = 3 * e                                        = 8.154 Volt at time t= 2 T voltage V ' = Vo e -t / T                 = 8.154 * e -2                = 1.103 Volts                = 1.103 Volts

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