# UBC PHAS Demonstration Room Catalog

### Site Tools

demonstrations:5_electricity_and_magnetism:5k_electromagnetic_induction:can_crusher:start

This is an old revision of the document!

# Can Crusher

The big bang capacitor, with the can-crushing apparatus connected.

## Description

A capacitor is used to produce an extremely high (but short lived) current around a tin can. This sudden change in flux causes an opposing current to be set up in the tin can. This current, acted on by the original magnetic field set up by the coil, causes a strong Lorentz force to be experience around the circumference of the can, evenly crushing the can inwards.

## Purpose

This demonstration shows the action of Lorentz force in a dramatic fashion. This also effectively illustrates how energy can be stored in capacitors and can also be used to talk about RC circuits. (as an example of an RC circuit with a very short time constant.)

## Apparatus

• 'Big Bang' capacitor (Same as used in the 'Big bang' capacitor demo)
• Can Crusher apparatus (wooden platform with switch and coil)
• Empty pop can

## Setup

Place wooden platform over the PVC pipes covering the capacitor ends. This part is tricky, you can't 'slot' the platform on, it needs to be lifted and lowered onto the PVC pipes from above. Attach the switch and coil to the capacitor leads as pictured below. Place the can inside the coil. If necessary, it can be fixed in place with some tape.

Once everything is hooked up, you're ready to run the demonstration.

The instructions below are also included on top of the 3kV power supply.

1. Plug in the solenoid that closes the circuit. The button on its power cable is a toggle switch rather than a momentary switch, so make sure it's turned off.
2. Unclip the wire short from the terminals. If for whatever reason they were not already in place, short the capacitor with the discharge wand.
3. Connect the power supply to the terminals.
4. Plug the power supply in. Turn it on, starting with the power supply set to 500V. As the meter approaches the set value, increase it in 500V increments until you reach 3kV.1) This will take about five minutes.
5. Once the capacitor is charged to 3kV, remove the leads from the capacitor by pulling the attached strings. Take utmost care in this step; pull them off the terminals in a way that guarantees they have no chance of touching you. Place them on the ground away from each other.
6. Turn off the power supply.
7. Press the toggle switch once to discharge the capacitor into the coil, and again shortly later to turn off the solenoid.
8. Use the discharge wand multiple times to ensure that the capacitor is fully discharged.
9. Return the wire short to the terminals, making sure a good connection is made.

## Notes

High voltage and a dangerous capacitor is used in this demo! Please ask for assistance from demo personnel if you have not operated this before. Always short the capacitor using the copper rod before touching anything with your hands to make sure it is fully discharged. Assume everything is at high voltage until proven otherwise.

Top view of the can crushing apparatus. Bottom left inside the acrylic box is the solenoid which, when energized, completes the circuit. The terminals are shorted in this picture, this shows how it should be stored.

front of the capacitor, without the can crusher apparatus attached

Aluminum beverage can before and after crushing.

Demo room information

 Location —- Maker Unknown Current State Working
1)
This seems to reduce the charging time by nearly half. This may be due to reduced current flow on the higher voltage settings.