An electrostatic mystery ...

I have a Wimshurst machine. It was originally built by my father, and restored by both of us during the 60's. It is now in need of a bit more restoration, which I hope to find time for soon. As to the principal that it works on... The main thing is charge separation, eg if you have a charged capacitor and you pull the plates apart, the Voltage will increase. This is reasonable enough, since you have reduced the capacitance so for the stored energy to remain the same the Voltage must go up. All very well, but where does the initial charge come from? Anyway, they work fine and are fun to play with, especially in a darkened room. They tend not to work so well in damp conditions. I think this one was originally described in ME, although it would be before the forties, which is where my own collection starts. When you start turning the handle, you can feel the load come on when the machine begins to charge.

Different materials tend to give different polarities when rubbed, and I would agree that probably the dye is making the difference.

Did you know that pulling sellotape off the roll generates low energy X-rays? If you do that in the dark you can see sparks too.

The Faraday Centre in Napier (a technology museum) has a Tesla coil...now that makes some serious sparks.

John

Err . . . . Aren't all X-rays high energy by virtue of their short wavelength?

Russell

During most of my working life I was a nurse, and a good place to find (and have fun with) is when making the beds in the morning, whip a sheet off the bed, the hold your finger 1/2" away from a radiator, or other earth point, and BANG, a good fat spark.

Ian S C

The school that I went to in London as a kid was Parmiter's Grammar School in Bethnal Green (London).

The school had fantastic science labs with Wimshurst machines, Kundts tubes, Roentgen tubes, precision chemical balances in glass cases, a planetarium, and an art teacher (G.R.Williams) who was in 'Who's Who'. The school even had a photography club with a well equipped darkroom for after hours use.

After 4th form one was allowed access for practical studies (not the chem lab, unfortunately) so many fascinating experiments were devised. I wound a Tesla coil one day and used it to demonstrate to parents on an open night how to make lightning come from my fingers - exciting stuff at 15, but more fun was running a battery through soapy water and lighting the bubbles with a wax-taper. One day my home-made radio picked up the BBC broadcasting a computer playing music "Daisy" - thus I was hooked.

Nowaday's elfin safety would crack down on such adventures, but I have kept an eye on the old school, they have re-located. I hope that they kept the old tools that made a kid so inquisitive.

* Danny M *

within the electromagnetic specturm x-rays also have their own range and energy. Indeed simplifying x-ray production as a voltage differential streaming electons to the anode to generate x-rays then the higher voltage gives 'harder' x-rays and indeed x-ray gneerators have an ally plate to block the low penetration stuff and reduce scatter.

Typical medical application about 45kvp for 3mAs to grab a pic of a cat's extremity onto modern digital detectors compared to say 110kvp for 1.5mAs to snatch a lower contrast but 'frozen' frame of a 50kg dog's heart

(peak kilovoltage for milliamp seconds)

I doubt sellotape x-rays would make it through bacofoil.

Before WW2 dad used to get the "Hobbies" magazine, and I remember reading through them when I was around 10, 12 years old, and one had an article on how to make an X-Ray tube from an old vacuum type incandescent light bulb. Can't remember anything about the HT power supply.

Ian S C

> is when making the beds in the morning, whip a sheet off the bed, the hold your finger 1/2" away from a radiator, or other earth point, and BANG, a good fat spark.

In the mother country, we use cotton sheets

Neil

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Ah, but if you used black silk and white silk sheets, we might get back to the original mystery.

MichaelG.

> black silk and white silk sheets

At least you're not suggesting fifty shades of grey..

Neil

black silk and white silk sheets

At least you're not suggesting fifty shades of grey..

How would you see the spark if you're wearing the blindfold?

Nathan

When first married me and mine had silk sheets on the bed, I think they were a wedding gift.

I remember messing around between the sheets play fighting and what not. Anyway the trouble and strife shot out her side and kissed the bedside cabinet good night. It was all taken in good spirit and she only laughed, I laughed myself breathless.

Learnt a good lesson on friction or lack of it that night.

Going back to the original post, all the theories are fine, but is there any evidence that anyone else replicated the experiments? Until they do the theorising is pointless.

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"Going back to the original post"

Thank you, John

My own investigations have so far found nothing specifically explaining, Symmer's results.

... Which is why I posted this 'mystery' on the forum; in the hope that someone may have seen something.

MichaelG.

Don't worry, they were cotton sheets, and wool blankets.

Don't know if it was the clothes he wore, but dad always got a shock when he got out of the car.

Ian S C

We had a 1966 Ford Anglia Super. The seats were upholstered in some sort of "plastic" leather. Almost every time that i got oui of the car, I used to get a good belt as I touched the door, with my feet on the ground. So my clothes and the seat were generating a couple of hundred volts or so. We cured it by making up cloth covers for the front seats. Being a two car, any rear seat passengers leaned on the door before touching the ground, so were not as highly charged, and felt nothing. If they did, they never complained!

Howard

We used to slide off the imitation leaher covered stools at work and could generate 14Kv

One of the first lessons learned (the hard way!) on S&R helos was DON'T keep contact with the winch cable when you first touch down - ground or water! Wet winching in Holyhead harbour towards the end of a fairly strenuous session on the wire, I forgot! I was breathing hard, mouth open and got a static short across my teeth - amalgum fillings! Quite startling! A few years previously at Thorney Island we were tasked to liaise with the Farnborough boffins doing research on helo static discharge. The boffins were in the Littlehampton lifeboat and we did several runs to check discharge levels. they told us afterwards that the majority were in the 150-170, 000 volts range! Given that I was acting as the end of line conductor, I'm assuming that the current levels were very low.

rgds

Bill

It used to be common for cars to have a chain hanging down at the rear to stop electrostatic build up, which later was replaced by a conductive plastic strip. I suffered from car sickness as a child and fitting the chain cured it.
At school we had a vandergraff generator and one experiment was to stand on a wax block, get charged up then, with hair standing on end, shake hands with another pupil. I found this made me feel sick reinforcing the theory that being charged was the cause of my car sickness.

When I first started teaching nearly 40 years ago we had more time and fewer 'safety recommendations' and two demonstrations were getting a group standing in plastic washing up bowls to hold hands and charging up the line with static electricity before asking the end pupil to touch a water tap and secondly to stand in a bowl oneself and light a Bunsen burner by sparking across to it. Lots of fun, but I suspect today the main objection would be to the expense of keeping 30 plastic washing up bowls for one experiment!

One of the most interesting manifestations of static discharge can still be seen if you still develop your own roll film. Loading a film into a developing spiral in a darkroom, when you get to the end where it is secured to the backing paper you need to tear it off. This usually produces a visible spark, but I have never seen it affect the film, surprisingly.

For big sparks look at this

**LINK**