# A Tiny Bowl Showcasing the Lorentz Force

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We have created a simple set-up in which the Lorentz force can be visualized. By letting a current run through a water with baking soda mixture and placing a magnet underneath this mixture, the fluid will make rotating motion around the electrodes.

An important term used in this instructable is an electrode. This is a conducting material (usually a metal) that allows current to flow from a certain substance to another. In this case the electrodes allow for the current to flow from a wire into a fluid and into a wire again.

## Step 1: Materials and Tools

The following materials and tools are needed for this set-up:

• 12 V adapter with a DC power cable. Note that the power cable will be cut open.
• 30 cm cable*. This will be used to make electrodes, so two pieces of copper, aluminium, graphite, platinum, etc. would be sufficient as well. Also, the copper will rust away, so having extra cable length to make multiple electrodes could be desirable.
• A disk shaped magnet. We've used one with a diameter of 2 cm.
• A small glass bowl. We've used a square bowl of 10 cm X 10 cm.
• Cardboard paper (about 15 cm^2).
• Glue.
• 20 cm X 15 cm piece of wood as a base.
• 1.5 g baking soda*.
• 100 ml water*.
• Food colouring.

* This is the amount needed to demonstrate at least once.

The following tools are needed for this set-up:

• Wire stripper. Although a stanley knife would work as well.
• Bull-nose pliers
• Spoon (to stir the water).

## Step 2: Wiring and Electrodes

Start off by using the wire stripper or stanley knife to strip the ends of the DC power cable for the adapter as shown on the first image on the right.

Then, strip the entire 30 cm cable so that you are left with a copper wire. Using the pliers, half the copper wire. We will now shape this so it becomes an effective electrode. Using the pliers, bend one end of the copper wire into a swirl and shape the other end into a 'hook' so that the electrode can sit on the edge of the bowl as shown on the second image on the right. Do this for the second half of wire as well. Place the electrodes on the edge of the bowl (across from one another) and press them against the sides of the bowl as shown on the third image on the right. Make sure that the swirly part of the electrodes are about 2 cm apart from one another. Reshape the electrodes as needed and cut off any excess wire.

To finish the electrodes, take the stripped ends of the DC power cable and tie each stripped end around the hook of one electrode.

## Step 3: Bowl Platform

For this experiment, a magnet needs to be placed under the bowl. To make this placement easier we have made a platform for the bowl together with a tool to push the magnet.

To make the platform, cut a 4 X 4 cm square out of the cardboard. Cut out smaller squares of 1 X 1 cm and create 4 stacks of tiny cardboard squares to create the legs of the platform. The number of smaller squares needed depends on the height of the magnet. Make sure that the platform is a little higher than the magnet, so that the magnet can easily slide underneath it. Glue the tiny cardboard squares together and glue them to the corners of the platform as shown on the first image on the right.

To make the magnet slider tool, cut out a 2 X 7.5 cm strip from the cardboard. From one end, cut off a semi-circle with a diameter of about 2 cm. The magnet should easily fit in this end of the cardboard strip as shown on the second image on the right.

Lastly, cut two strips of 12 X 1 cm and a strip of 4 X 1 cm. These strips will act as the 'fence' for the magnet and its slider. Glue all of the cardboard components, except the slider onto the piece of wood as shown on the left image.

## Step 4: Performing the Experiment

Pour the water into the bowl and place this onto the cardboard platform. Slide the magnet under the bowl and connect the DC power cable to the adapter. If bubbles start to form around one of the electrodes it means that current is running through the wires as shown on the left image. Add the baking soda and stir if needed to make the baking soda dissolve quicker. You will likely be able to see that the baking soda is rotating around the electrodes. Add some food colouring to the water so that these rotating motions become more visible as shown on the image on the right. You have now shown the workings of the Lorentz force in a small, simple experiment.

Note: One of the copper electrodes will degrade and its surface colour will become turquoise, while the other electrode turns black. If you want to perform this experiment multiple times or for longer periods of time, it is recommended to make multiple copper electrodes in advance. Graphite or platinum electrodes could be used instead as these materials will not degrade.

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## Discussions

Very interesting, and nice to see. Thank you!