Open vs Closed Circuit: A Basic Introduction

This article is a summary of the YouTube video ‘Open Circuits, Closed Circuits & Short Circuits – Basic Introduction’ by The Organic Chemistry Tutor

Written by: Recapz Bot

Written by: Recapz Bot

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How does it work?
The video explains open, closed, and short circuits; an open circuit has no current, a closed circuit allows current, and a short circuit is dangerous.

Key Insights

  • 1. The video explains the difference between open circuits, closed circuits, and short circuits.
  • 2. An open circuit has a break in the circuit, and no current flows through it. The light bulb does not turn on in an open circuit.
  • 3. A closed circuit has a complete path for current to flow, with the switch closed. Current flows from the positive terminal of the battery, through the light bulb, and returns to the battery's negative terminal. The light bulb turns on in a closed circuit.
  • 4. A short circuit is a circuit with little or no resistance, allowing a dangerously high current to flow. It can cause overheating and fire hazards.
  • 5. Fuse and circuit breaker are devices used to protect circuits from high currents. A fuse breaks the circuit by snapping its wire if the current exceeds its rating. A circuit breaker turns off the circuit but can be turned back on.
  • 6. A circuit with a resistor is not a short circuit because the resistor limits the amount of current flowing through the circuit.

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Now, in this tutorial, we’re going to talk about the difference between an open circuit, a closed circuit, and a short circuit.

So let’s connect a battery to a light bulb, and we’re going to have a switch. And in this circuit, I’m going to connect a battery to a light bulb with another switch. And in this circuit, the battery is going to be connected to a resistor. And in this circuit, the battery is just directly connected to itself.

Which circuit is the open circuit, and which one is the closed circuit? And also, identify the short circuit. Now there are four circuits, so one answer is going to apply to two circuits.

So which one is the open circuit? The open circuit is the one that has an open switch. As you can see, there’s a break in the circuit. And whenever there’s a break in a circuit, no current will flow. So the current in this circuit is zero, which means the light bulb is not on.

On the right, we have a closed circuit. Because the switch is closed, there’s a path for the current to flow. So the current is going to flow from the positive terminal, pass through the light bulb, and return back to the battery at the negative terminal. And because the switch is closed, some of the electrical energy will be converted into light energy. So the light bulb is going to be on if the battery is powerful enough, of course.

Now, on the bottom right, we have a short circuit. A short circuit is a circuit that has little or no resistance. Every light bulb has an internal resistance, so the current is limited based on the resistance of the light bulb. But in this battery or in this circuit, there’s almost no resistance. And so the current that flows in this circuit will be dangerously high. And so if you have a large current flowing through a wire, it can heat up the wire and cause a fire, so that’s dangerous. And so that’s why you want to avoid short-circuiting a battery.

Now, because short circuits are so dangerous, you need to have elements in the circuit to prevent these things from happening. One device you could use is called a fuse. And a fuse looks something like this. And there’s like a very thin metal filament on the inside. And let’s say if this fuse is rated to be a 20 amp fuse, if 20 amps or more of current flows through the fuse, the fuse is designed to snap. So this wire is going to break. The connection will be broken. And so it creates an open circuit, and it prevents other devices in the circuit from being damaged due to the high currents that are flowing. So you’re going to have a snap wire. And so now you have an open circuit. And so a fuse is designed to protect a circuit from dangerously high levels of current.

Now, another device that works the same way is a circuit breaker. Now, a circuit breaker is a circuit where if the current is too high, it turns off the circuit. Now, the good thing about a circuit breaker is if a high current trips it, you can always turn the circuit breaker back on. If too much current flows through the circuit, the circuit breaker will stop the circuit. But then you can always turn the circuit breaker back on, so you don’t have to replace it. With a fuse, once the fuse pops, once it busts, you have to replace it with another fuse. And if you don’t have another fuse around, then your device won’t work. And so that’s the advantage of a circuit breaker over a fuse. Because you don’t have to replace the circuit breaker if too much current flows through it. It will just automatically turn off, and then you can turn it back on with a switch.

Now, the last circuit is a closed circuit. By the way, a short circuit is also a closed circuit because current does flow in this circuit. There are no breaks in a circuit. Now, this circuit is not a short circuit because we do have a resistor. And the resistor will limit the amount of current that is flowing through the circuit. So any type of device like a motor, a speaker, a light bulb, they all have an internal resistance. And so they limit the amount of current that will flow through them. But if you just have a wire, which has very, very little resistance, it’s going to allow a large amount of current to flow through it. So that can be dangerous.

This article is a summary of the YouTube video ‘Open Circuits, Closed Circuits & Short Circuits – Basic Introduction’ by The Organic Chemistry Tutor