# Please Explain when an RC Circuit Opens - Effect on a Light bulb

• ncm2
In summary, when the switch is opened in the given circuit, the light bulb will gradually dim as the capacitor discharges through it, but depending on the amount of charge in the capacitor, it may go out immediately or continue to shine for a short period of time before fully extinguishing.
ncm2

## Homework Statement

Initially the switch is closed in the circuit shown and the light bulb is shining brightly. What happens when the switch is opened? (diagram in attached link)
1. The bulb goes out immediately.

2. The bulb gets gradually brighter.

3. The bulb gets gradually dimmer.

4. It cannot be determined.

5. The bulb continues to shine without a change in brightness.

Vc=Vo*exp(-t/RC)

## The Attempt at a Solution

I believe that the capacitor should cause the light to gradually dim. However, I also think that the open switch should mean no current flow, which would mean the bulb would immediately go out.

Any explanation is much appreciated

#### Attachments

• CapacitorBulbDiagram.jpg
1.8 KB · Views: 588
I can't see the picture.

I suppose that the capacitor is in parallel with the light, and the voltage source is DC. (If different then ignore my comments.)

The charge in the capacitor will continue to flow, despite no current from the power source, and the light will - depending on how much charge is available in the capacitor - dim slowly or quickly, as it discharges through the light (current) until extinct.

You can see this on some devices like computers when you pull the plug the power on light remains lit and then dims.

I will try to explain the diagram for you, but it sounds like it probably will dim gradually.

The diagram is a box, with a line through the middle, creating a figure 8 shape. Voltage source is on the left, which is connected in series to the light bulb which is on the top line, to the left of the middle line. The capacitor runs on a wire down the middle. Then the Switch is on the far side of the box from the voltage source.

Hopefully that helps a bit. I don't know if it matters that the switch is not in series with the capacitor?

It sounds like the capacitor is in || with the lightbulb.

If there is a path remaining for the cap to discharge - one side to the other through the lightbulb, then that's what it will do - dim.

i could be wrong (noob here) but it seems to me that (from the now provided diagram) that the capacitor will be fully charged on the opening of the switch, giving no time for the current to ramp down so it will shut off quickly?

## 1. What is an RC circuit?

An RC circuit is an electrical circuit that consists of a resistor (R) and a capacitor (C) connected in series. It is used to control the flow of electric current and can be found in various electronic devices such as radios, televisions, and computers.

## 2. How does an RC circuit work?

An RC circuit works by storing and releasing electrical energy. When a voltage is applied, the capacitor charges up until it reaches the same voltage as the power source. The resistor controls the flow of current, allowing the capacitor to charge and discharge at a controlled rate.

## 3. What happens when an RC circuit opens?

When an RC circuit opens, it means that there is a break in the circuit and no current can flow through it. This results in the capacitor no longer being able to charge and discharge, causing the circuit to stop working.

## 4. How does an open RC circuit affect a light bulb?

When an RC circuit opens, the flow of current to the light bulb is interrupted. This means that the light bulb will no longer receive the necessary electrical energy to emit light and will turn off.

## 5. How can an RC circuit be fixed if it opens?

If an RC circuit opens, it can be fixed by identifying and repairing the break in the circuit. This can be done by checking all the connections, replacing any damaged components, and ensuring that the circuit is properly closed. It is important to handle all electrical repairs with caution and to seek professional help if needed.

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