Sharing thoughtful approaches to teaching physics with the wider world.
Van de Graff generator
23 January 2018 at 11:23 #49599
A tweet from @suziesheehy showed a fern being attracted to a VdG
Made me think of all the things you can do with a VdG
Here is a playlist of some of demonstrations
I use the VdG when teaching AQA turning points and discussing how Hertz reasoned that as a spark jumps back and forth across a gap of an induction coil, it must set up rapidly changing electric and magnetic fields. According to Maxwell’s theory, these changes propagate through space as electromagnetic waves.
I use an old radio for this
After talking to my dad who was a radio officer or “sparky” I built a coherer
I met a VdG once that had about the limit of charge build up you would want to make in a classroom. In the playlist it is the one lifting up the Japanese Yen coins. They each have a mass of 1g!
This is what it did to a large florescent tube
This next video is in the playlist but I thought it deserved some comment. You can show the charge on the dome and also how charge can only flow one way through an LED. I would recommend the LED was attached to a metre ruler and earthed via the VdG’s earth.
The VdG below is from Timstar. The best thing about this VdG is it has a variable speed.
23 January 2018 at 11:49 #49600
I use a piezo electric gas lighter to fire up my coherer, I can transmit from several metres away on a good day.
BTW Electrostatics and plants are a big thing for bees. I’ve seen research where they showed that bees could detect the potential of a flower so that they would know if it had been recently visited by another bee. Like helicopters bees are little static machines that will alter the charge on a flower when they visit. Incoming bees can pick up these differences and move to another flower where there might still be some nectar and pollen.
23 January 2018 at 12:08 #49601
Brilliant Nick, I am adding that about the bees and static into my teaching. There was a little about that in the twitter discussion
23 January 2018 at 12:40 #49602
Have you seen the clips about static and spider webs? High speed filming shows that webs actually bend out towards flying insects for the same reason.
When Darwin spoke of the spiders that he saw flying through the air attached to gossamer threads lifted on the wind he is said to have commented on their direction relative to the ship. Apparently it can be explained by the electrostatics though, of course, we can’t reproduce that one to the same extent so that’s not proven.
1 February 2018 at 21:10 #49690
Spiders seems to be my theme this week for me and my students. The latest Physics Review arrived for our students and there is an article by Mike Follows on Spider-Man’s silk and Young’s modulus. I told my students about the electrostatic properties you brought to my attention Nick. I also showed them how a spider tunes each thread to a unique frequency so it can identify the direction of prey stuck in the web.
I Like to show students how in the early days of particle accelerators VdG were used.
Very large VdG, the building behind me here was built to house a VdG at Daresbury
2 February 2018 at 07:19 #49691
In my playlist (the first video) you can see a linear accelerator. The first version of this I came across was a salad bowl accelerator. I use this when teaching particle physics and electrostatics.
The above version uses an aquadag coated pith ball. The one below uses a table tennis ball coated in aquadag.
A great article on the use and construction by Particle accelerator physicist & Royal Society University Research Fellow Suzie Sheehy @suziesheehy
Suzie has made some great videos with the RI. I show this one to my students.
7 February 2018 at 09:25 #49735
Another really nice one is to make a small hole in the centre of Al cake holders and pass a thread through them. Stick the thread with some tack on the dome and vertically up on the ceiling. When you turn on the VDG the cake holders separate and float
11 February 2018 at 19:25 #49773
I have always wanted to try this ever since you suggested it to me before Alessio. So thanks for reminding me of this. Here is my prototype
11 February 2018 at 21:54 #49779
I used my smallest foil trays
To make a nice vertical thread I wanted my thread to come up from the center of a banana plug. These usually fit in the top of VdG
I used a hole punch to make an aligned hole in all the trays at once.
I used to have a set of gasket making punches which would have been ideal. The punch was a point so pushed foil that could catch the other trays.
I punched through both ways and then flattened any pieces of metal at the edge of the hole.
I tried the foil trays balanced on the banana plug to see if they would accrue enough charge to fly away from each other due to electrostatic repulsion.
To attach the thread to the banana plug I wrapped it through a ball of blue tack a few times then rolled this into a sausage shape.
I then pushed this firmly into the plug.
I laid the thread over a lamp and trapped it under tension between a hammer and the table.
It took a few attempts to align the thread vertical to get the best lift.
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