The Wimshurst Machine

Introduction:

You may have heard of the Van de Graph generator - a tall machine with a large metal ball on top that generates an electrical field. It will shock anything that gets close and makes your hair stand up on your head! But have you ever heard of a Wimshurst Machine? It's a device that uses a slightly different technique, but delivers the same shocking results. Visit here for the Social Studies component and here for the ELA component

Driving Question:

The driving question behind my project is "How does the Wimshurst machine produce a charge?" First, it's important to look closely at the device. As you can see, each metal sector moves very close to the collection comb. When the disks start to turn, the metal segments rub against the brushes. This rubbing effect creates an electric charge in each metal segment, which is transferred through induction to the Leyden jars. According to the Conservation of Energy principle, mechanical energy from you turning the wheel is changed into electrical energy

TASK 6 STARTS FROM HERE

Investigation (Guiding) Questions

What do you observe when you spin the Wimshurst machine?

• • You observe the buildup and then release of a static charge caused by rotating the disks.

How do you know that charge is being produced when the Wimshurst machine is spinning?

• • You can tell by the smell of ozone and by moving the rods close together to see if there is any discharge.

Where is the charge coming from and will the Wimshurst machine ever run out of charge?

• • The Wimshurst machine will never run out of charge because it is simply amplifying an imbalance of charge between the two disks.

What evidence is there that an electric field is being produced by the Wimshurst machine?

• • There is evidence an electric field is being produced because of the machine’s effects on small particles that will align themselves

What tools can you use, and how would you use them, to prove that an electric field is being produced by the Wimshurst machine?

• • You can put pieces of styrofoam on the table near the machine and observe its effects. Then, put them inside a faraday cage and see if there is a change.

What are everyday examples of electric fields that demonstrate the same properties?

• • Van de Graph generators, static electricity from blankets, carpets, etc.

What are two electrification methods for transferring charge from the Wimshurst machine to other objects?

• • Attaching leads from the leyden jars or by holding on to the discharge electrodes

How can you show both of these electrification methods using the materials at your disposal?

• • Attaching leads from the leyden jars to a charging sphere, or hold a neon wand on the discharge electrodes.

Synthesis Questions:

1. What would happen to the charge produced by the Wimshurst machine if the handcrank on the

machine was turned in the opposite direction? Would this change how the charge is produced? Why?

• • If the handcrank was turned in the opposite direction, it would simply reverse the polarity of the charge going into the leyden jars. It wouldn’t change how charge is produced because the rules of induction still apply.

2. What would happen to the performance of the Wimshurst machine if you were to operate it in a

humid environment? Why?

• • If you operated it in a humid environment it would be more difficult to build up a static charge because the water molecules in the air would dissipate the voltage.

3. Can charge be transferred (electron transfer) through the air without a spark? If yes, what is an

example? If no, why not?

• • Yes, it can be transferred through induction/ through an electric field. An example of this is turning on a light bulb by holding it near a source of electricity.

4. Imagine a metal pie pan filled with very small bits of dry paper. How would the bits of paper react if

the metal pan was electrically connected to one of the electrodes on the Wimshurst machine when you

began to turn its crank? Why?

• • The bits of paper would move around and align themselves to the electrical current moving through the pie pan. This is because electricity can have an electrostatic influence on small particles (like doll’s hair, confetti, etc.)