### Short Circuits Virtual Lab

A short circuit is a circuit that includes no resistance. Short circuits are dangerous, but also very interesting, and sometimes counterintuitive. To learn about short circuits, we are going to build some short circuits using a simulation. No one will get hurt, and we'll learn a little about how short circuits work.

This is a version of the Series and Parallel Circuits lab conducted virtually, using the simulation below. I recommend you select "intro" mode, although you can use either "intro" mode or "lab" mode.

Simulation provided by PHET interactive simulations at the University of Colorado at Boulder

#### Virtual Materials

• A single battery
• A single light bulb
• Several wires

#### Procedure

1. Put the battery in the holder and connect one end of the battery to the other, without including any light bulb in between, only a wire:

This is a short circuit! Short circuits are dangerous. How does the simulation represent this?
2. Is there electric current running in your short circuit? Is it a high or a low current?
3. Short circuits are dangerous because, with no resistance, there is a very high amount of current! Remember, $$V = IR$$ and $$I = \frac{V}{R}$$, so if $$R$$ is very low, then $$I$$ is very high. People often believe that high voltage is very dangerous, but it is actually high current that tends to make danger. When there is high current is when you start to feel your circuit get warm. In fact, most household items can take only about 15 amps before they break.
Look at the voltage of your battery. If the wire provides only 0.1 Ohms of resistance, find the current and power of your circuit with the formula $$V = IR$$ and $$P = IV$$ Do you think this is safe?
4. Shorting a Light Bulb: Connect a light bulb to a battery so that it lights:

Now, add another wire between your bulb and battery like so:

What happens to the light bulb the moment you add the wire? What is the current running through the wire? Do you have a short circuit with current running?
5. Imagine that the wire is a big open highway, the light bulb (a resistor) is a traffic jam, and the electrons (moving around the circuit) are cars trying to get from one end of the battery to the other. Which path would the electrons take, the path with the light bulb or the path without the light bulb? Based on this metaphor, why do you think the light bulb shuts off (or dims down) when another line opens up?
6. A "Short Circuit" that is a Long Circuit: Connect a light bulb to a battery so that it lights:

Now, add another wire that goes the long around the light bulb:

What happens to the light bulb the moment you add the wire? What is the current running through the wire? Do you have a short circuit with current running?
7. A short circuit always happens because there is a path around the light bulb that includes no resistance. It does not matter if this path is short or long. Wires have almost no resistance, so if there are lots of wires, it can still be a 'short' circuit. Using the same explanation you had above, explain why the light bulb turns off, even though the path through the wire is much longer than the path through the light bulb.
8. Your friend builds this circuit:

Upon noticing the light bulb does not light, your friend says "The light bulb does not light because it is farther away from the battery than the other wire." Is your friend correct? If not, create a 'counterexample,' that is, draw another circuit which you can use to prove that his reasoning is incorrect. Explain what happens when you build your counterexample