P7.3-7. (a) Determine the energy stored in the capacitor in the circuit shown in Figure P7.3-7 when the switch is closed and the circuit is at steady state.

(b) Determine the energy stored in the capacitor when the switch is open and the circuit is at steady state.

P7_3_7

Figure P7.3-7

 

(a) Determine the energy stored in the capacitor in the circuit shown in Figure P7.3-7 when the switch is closed and the circuit is at steady state.

 

When switch is closed, the circuit is

When the circuit is in steady state, the capacitor acts as an open circuit.  So the voltage across the capacitor is the same as the 75 kΩ resistor which is in parallel with it.  The steady state circuit is a simple voltage divider circuit with two identical resistors each 75 kΩ, so the voltage divides evenly and is 6 volts.  So the energy stored can be obtained by

 

 

(b) Determine the energy stored in the capacitor when the switch is open and the circuit is at steady state.

 

When switch is open the circuit looks like

In Steady State there is no current flow, so there is no voltage dropped across the 75 kΩ resistor and the voltage on the capacitor is therefore the 12 V of the voltage supply so the energy stored is

 

 

 

 

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This page last updated on April 5, 2019