## Sunday, 2 June 2013

### Hair Club for Van Der Graaf Machines and Einstein Hair

This is the third post on Van Der Graaf demonstrations, and serves as an important theory point before you discuss charge distribution in hollow objects and air discharge and lightning rods.

### Hair Club for Van Der Graaf machines

You will need a hair attachment for your Van Der Graaf machine. Typically your machine will come with one - usually an electrical banana plug with a bundle of hair glued in the end, that plugs into the top of the machine. These always work, even if the weather conditions kill the rest of your demonstrations. If you don't have one, beg and plead your head of department to buy one.

These (the picture below) don't work unless conditions are perfect. Bleh.

http://sci-toys.com/scitoys/scitoys/electro/electro6.html

Make sure that you discharge the main sphere before you plug in the attachment, and then turn the machine on. Quite quickly, the hairs will rise and drift away from each other.

### Points of Theory

• The hair has the same charge as the main sphere. The charge moves into the hairs.
• Like charges repel, (You did teach this beforehand, didn't you?) so the hairs try to get as far away from the sphere and each other as possible.

### Extras

• Wave the discharge sphere near the hairs. The hairs will all be attracted to the discharge sphere. Unlike charges attract. (Kind of. What's actually happening is that the hairs are attracted to an induced charge in the discharge sphere. You can see for yourself that when you bring your hand near the hairs, they behave the same. Since you're touching the neutral ground, it's not a simple as negative being attracted to positive. Not worth teaching this to the kids, as the next post will deal with this any case).
• Bring the discharge sphere near the main sphere - the sparks are less intense if they're present at all. Talk about air discharge and use this to explain why the students' arm hairs feel prickly near the machine, but make sure that you mention that air discharge only enhances this prickly feeling - that the electrostatic field would still exist if the machine was in a vacuum. Mention that small, pointy objects enhance air discharge, but save the explanation until you get to these demonstrations.

### Einstein Hair

Once the students see the toupee demonstration, they will want to see this demonstration. This is why it's best to rebook the whole series of demonstrations if you get poor weather. You want this one to work, but it takes a very large charge before anything happens at all.
1. This works best for someone with long, very fine straight hair, who is wearing thick rubber soled shoes. Blonde seems to work best for some unfathomable reason. Let others try if you have really good weather, but do your best to convince your chosen victim to give it a go.
2. As mentioned in this post, the student won't be zapped if there isn't an imbalance of charge between the sphere and themselves. Make sure to fully discharge and turn off the Van Der Graaf machine before the student touches the sphere.
3. Reassure the student that they won't be zapped if they follow your instructions closely. You will have to use all your persuasive skills here if they're at all nervous, especially if they're the only person in the class with suitable hair. Make sure the student isn't near any metal (such as handles or water taps) and that they know not to remove their hands until you tell them it's safe.
4. Once they have both hands on the machine, turn the machine on, and hold the discharge sphere in your hand, well away from their body. (Don't ever bring the discharge sphere into contact with their body, even as a joke).
5. If you're lucky, their hair will start to rise. Encourage them to do the "shampoo hair toss" to get the individual hair fibers to separate and rise.
6. Discharge the main sphere with the discharge sphere, (Repeat. Don't touch the student with the discharge sphere, you want metal to metal.) hold the discharge sphere on the main sphere, and turn the machine off. It is now safe for your student to take their hands off the sphere and move away.

### Extras:

Don't do the following with nervous students - you want to encourage such a student to participate in demonstrations in the future.
• With a confident student (don't worry, they'll let you know who they are - "Can I go next?") you can zap them by holding onto a water tap and touching your knuckle to their ear or elbow while they're charged up. The ear works best (because it hurts more *mwah hah haaah*), but if it's a student of the opposite sex, for legal reasons you're safer to use their elbow. Fifty percent of the time, you'll be the one that gets zapped, but you can play that up as well. On a good day, the students in the audience will jump because they can hear the crackle of the discharge.
• Or you can emphasis that they're safe as long as they don't let go - then pretend to leave them hooked up to the machine as you walk off. ("MR HEAG-NEY!!!" o_O) The really confident ones will let go and walk off by themselves, and promptly zap or get zapped when they sit back down or touch a friend.
• On really good weather, you can have two, three or four students holding hands, with one touching the machine. Get the last person to touch a metal tap - everyone in the line will jump as they get zapped.
Don't spend too much time with these demonstrations, you've still got a lot to get through.