- #1
tomcat017
- 7
- 0
Hello all,
I have a quick, albeit probably ignorant (forgive me) question generated by (bu dum) observations of a van de graaff generator.
In particular, two distinct scenarios caused me to question what was going on.
Scenario 1 – I’m standing on a plastic stool, with one hand on the generator’s dome. I’m holding a nail in the other hand. I point the nail at a grounded discharge electrode, and hear the effects of escaping charge. I bring the nail close to the grounded electrode until (at a very close distance) visible arcs form. I then put the nail in contact with the discharge electrode. I feel no appreciable sensation.
Scenario 2 – I’m standing on the ground, in sneakers, not in contact with the generator dome. In one hand, I’m holding a neon-filled gas tube. I being the tube near the dome and hear charge escaping as the ionizing gas in the tube emits light. I feel no real sensation. I assume this is due to small amounts of charge leaking off of the dome. I get a bit too close, and a large (~6”) arc jumps from the dome to the gas tube. I’m holding the glass envelope, and feel…an appreciable sensation in my hand and in my right foot.
In both cases, I am serving as the conductor that connects the dome to the ground. In scenario #1, I feel nothing, while in scenario #2…definitely something. Why does this happen?
Here’s my preliminary suspicion – please correct me where I’m wrong. In scenario #1, lots of charge is leaking off my body (hair and fingers both relatively pointy). By the time the nail contacts the discharge electrode, potential difference is low (why the arc is so short), and so the sensation produced by resulting current is minimal. In scenario #2, the dome retains almost all of the 200 kV potential (it is a sphere), and none leaks (save minimal charge prior to reaching the critical distance) until I get close enough, and then – full discharge. The resulting current produces a substantial sensation.
Is that it? Or is there more/else to it?
Some follow-up questions.
1. When I got the shock sensation, why was it felt in my hand and foot, but not in between?
2. Does touching the discharge electrode with the nail result in less sensation that if I had contacted it with my finger? Why? Is there something special about the point where the arc occurs, as it pertains to sensation? More substantial that the current flowing from me into the nail without the arc?
3. Is there a better way to demonstrate gas ionization in this fashion (without taking the shock every time)?
4. There are videos on youtube of chains of 5-10 people in contact with the generator dome. When the last person in the chain is touched, there appears to be a substantial sensation. Why is the charge not leaking off the people (x10) in such large amounts that contacting the final person has no result? Moreover, since all of the people are standing on the floor, why does an 11th person (also standing on the floor) cause significant discharge/sensation? When he contacts the chain, he is no more grounded than each of the other participants, no?
Thank you in advance for any clarity you can provide! Please feel free to criticize my understanding, and please do forgive me if this is obvious to you.
I have a quick, albeit probably ignorant (forgive me) question generated by (bu dum) observations of a van de graaff generator.
In particular, two distinct scenarios caused me to question what was going on.
Scenario 1 – I’m standing on a plastic stool, with one hand on the generator’s dome. I’m holding a nail in the other hand. I point the nail at a grounded discharge electrode, and hear the effects of escaping charge. I bring the nail close to the grounded electrode until (at a very close distance) visible arcs form. I then put the nail in contact with the discharge electrode. I feel no appreciable sensation.
Scenario 2 – I’m standing on the ground, in sneakers, not in contact with the generator dome. In one hand, I’m holding a neon-filled gas tube. I being the tube near the dome and hear charge escaping as the ionizing gas in the tube emits light. I feel no real sensation. I assume this is due to small amounts of charge leaking off of the dome. I get a bit too close, and a large (~6”) arc jumps from the dome to the gas tube. I’m holding the glass envelope, and feel…an appreciable sensation in my hand and in my right foot.
In both cases, I am serving as the conductor that connects the dome to the ground. In scenario #1, I feel nothing, while in scenario #2…definitely something. Why does this happen?
Here’s my preliminary suspicion – please correct me where I’m wrong. In scenario #1, lots of charge is leaking off my body (hair and fingers both relatively pointy). By the time the nail contacts the discharge electrode, potential difference is low (why the arc is so short), and so the sensation produced by resulting current is minimal. In scenario #2, the dome retains almost all of the 200 kV potential (it is a sphere), and none leaks (save minimal charge prior to reaching the critical distance) until I get close enough, and then – full discharge. The resulting current produces a substantial sensation.
Is that it? Or is there more/else to it?
Some follow-up questions.
1. When I got the shock sensation, why was it felt in my hand and foot, but not in between?
2. Does touching the discharge electrode with the nail result in less sensation that if I had contacted it with my finger? Why? Is there something special about the point where the arc occurs, as it pertains to sensation? More substantial that the current flowing from me into the nail without the arc?
3. Is there a better way to demonstrate gas ionization in this fashion (without taking the shock every time)?
4. There are videos on youtube of chains of 5-10 people in contact with the generator dome. When the last person in the chain is touched, there appears to be a substantial sensation. Why is the charge not leaking off the people (x10) in such large amounts that contacting the final person has no result? Moreover, since all of the people are standing on the floor, why does an 11th person (also standing on the floor) cause significant discharge/sensation? When he contacts the chain, he is no more grounded than each of the other participants, no?
Thank you in advance for any clarity you can provide! Please feel free to criticize my understanding, and please do forgive me if this is obvious to you.