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Hi everyone. My problem is for an assignment in a network analysis course. I attached the homework page as a pdf.

My problem involves an R-L circuit with a switch. There is a 100 V source, and switch that is initially closed, followed by a .25 H inductor and a 200 Ohm resistor in series. After being closed for a while, the switch is opened. The question says "To reduce the voltage that appears across the switch, it is proposed to connect a capacitor as shown"...the capacitor will be connected between the switch and the inductor+resistor and be parallel to them. "Choose a capacitor that will limit the voltage appearing across the open switch contacts to 150 V. Specify the capacitor completely by stating not only its value but also its voltage rating."

Not really sure what equations to include that would be helpful. The concept requires knowing all of the necessary equations, as far as I can tell.

I determined that the current across the inductor at 0- and 0+ is 0.5 A. It appears as though the capacitor is not actually in the circuit and then is added at t=0 (since it says it is proposed to connect a capacitor), so I don't know how to approach it since the capacitor will not have any Voltage from t<0 and therefore none for V>0.

So, basically I don't understand how to work it other than perhaps to work backwards plugging in 150 V and then determining somehow what the corresponding capacitance might be, even if you don't have any initial voltage across the capacitor.

## Homework Statement

My problem involves an R-L circuit with a switch. There is a 100 V source, and switch that is initially closed, followed by a .25 H inductor and a 200 Ohm resistor in series. After being closed for a while, the switch is opened. The question says "To reduce the voltage that appears across the switch, it is proposed to connect a capacitor as shown"...the capacitor will be connected between the switch and the inductor+resistor and be parallel to them. "Choose a capacitor that will limit the voltage appearing across the open switch contacts to 150 V. Specify the capacitor completely by stating not only its value but also its voltage rating."

## Homework Equations

Not really sure what equations to include that would be helpful. The concept requires knowing all of the necessary equations, as far as I can tell.

## The Attempt at a Solution

I determined that the current across the inductor at 0- and 0+ is 0.5 A. It appears as though the capacitor is not actually in the circuit and then is added at t=0 (since it says it is proposed to connect a capacitor), so I don't know how to approach it since the capacitor will not have any Voltage from t<0 and therefore none for V>0.

So, basically I don't understand how to work it other than perhaps to work backwards plugging in 150 V and then determining somehow what the corresponding capacitance might be, even if you don't have any initial voltage across the capacitor.