Milikan's oil drop experiment?

[Manticore]

I think "difference" or "differential" would have been the appropriate term.

 

Whoops. I was half asleep when I wrote 'gradient'.

[studiot]

Thank you for the picture, Sensei, but please check your directions.

 

It shows the important fact that

 

The arrows point in the same direction all the way from the blue to the red.

 

@Capiert, it is not an unreasonable guess that the two fields somehow cancel in the middle.

 

Unfortunately, as swansont said, it is a guess and not correct Physics.

 

The key to this is in the fact that the lines of force point inwards at negative charge and outwards at positive

 

https://www.google.co.uk/search?q=lines+of+force+at+positve+and+negative+charge&ie=utf-8&oe=utf-8&client=firefox-b&gfe_rd=cr&ei=NH1iWZbuFKqn8wexs6S4AQ

 

So the lines of force between the plates are continuous frok one plate to the other.

They do not change over half way.

Edited July 9, 2017 by studiot

[Capiert]

      On ‎2017‎ ‎07‎ ‎07 at 5:32 PM, Capiert said:

The (capacitor's) plates

are physically separated (naturally, no argument there);

but the(ir) (positive & negative, as) "sum"

of their surface_charges (sigma=+/- Q/A)

at the "position" of the oil drop

has a cancelation effect

(=resulting total, which is less (than a single plate)).

On ‎2017‎ ‎07‎ ‎07 at 6:38 PM, swansont said:

No, it (=?) absolutely does not have a cancellation effect. You cannot sum the charges in this situation.

The only way you could look at them as cancelling is if you are very far away from the capacitor plates. But that is decidedly not true for an oil drop that is between the plates.

Please identify "it"=?

 

I'( ha)ve taken a 10 cm diameter styropor ball,

 wrapped it with Al foil (to be like a Gaussian sphere, e.g. the center is always zero (charge?, E_field?),

 so it's a self_discharging single plate capacitor, being charged externally from the environment (surroundings).)

 & connected it to a J-FET input oscilloscope's probe.

 

The (oscillo)scope indicated RF noise (voltage on the ball, exponentially)

 when that ball was brought near the ground

 (or walls, ceiling).

(Much larger) AC voltage also showed (on the display) when the ball neared AC cables,

 & increased as distance decreased.

 

I made 2 large capacitor plates (each 1 m x 0.5 m x 0.1 m,

 from styropor plates covered with Al foil),

 separated them (e.g. d~0.5 m) as a parallel plate capacitor

 & connected them (in parallel) to the AC (house) power (outlet, via wires & alligator clips).

 

I moved the ball_probe between the 2 plates (back & forth).

As the Al_ball probe neared an inside plate surface

 the AC voltage ((that) displayed on the oscilloscope) increased (exponentially);

 & the polarity was opposite for the other plate;

 but (ruffly) zero (voltage) in the middle between the plates.

That looks to me like (a single probe) plus+minus (=adding) cancelation

 so please identify what I measured.

(=What was I measuring? Electric potential?)

Edited December 11, 2017 by Capiert

[swansont]

8 hours ago, Capiert said:

      On ‎2017‎ ‎07‎ ‎07 at 5:32 PM, Capiert said:

The (capacitor's) plates

are physically separated (naturally, no argument there);

but the(ir) (positive & negative, as) "sum"

of their surface_charges (sigma=+/- Q/A)

at the "position" of the oil drop

has a cancelation effect

There is no cancellation in this geometry.

Quote

(=resulting total, which is less (than a single plate)).

Please identify "it"=?

What you had said that I was responding to, and repeated above. The "summing" of their charges (which is something you have made up here) does not have a cancellation effect. There is no physics that justifies the summing. There is no cancellation in this geometry. repeating it does not make it true.

Give a reason backed up by physics for claiming that you can sum the charges, and gives cancellation.

Quote

I'( ha)ve taken a 10 cm diameter styropor ball,

 wrapped it with Al foil (to be like a Gaussian sphere, e.g. the center is always zero (charge?, E_field?),

 so it's a self_discharging single plate capacitor, being charged externally from the environment (surroundings).)

 & connected it to a J-FET input oscilloscope's probe.

 

The (oscillo)scope indicated RF noise (voltage on the ball, exponentially)

 when that ball was brought near the ground

 (or walls, ceiling).

(Much larger) AC voltage also showed (on the display) when the ball neared AC cables,

 & increased as distance decreased.

 

I made 2 large capacitor plates (each 1 m x 0.5 m x 0.1 m,

 from styropor plates covered with Al foil),

 separated them (e.g. d~0.5 m) as a parallel plate capacitor

 & connected them (in parallel) to the AC (house) power (outlet, via wires & alligator clips).

 

I moved the ball_probe between the 2 plates (back & forth).

As the Al_ball probe neared an inside plate surface

 the AC voltage ((that) displayed on the oscilloscope) increased (exponentially);

 & the polarity was opposite for the other plate;

 but (ruffly) zero (voltage) in the middle between the plates.

That looks to me like (a single probe) plus+minus (=adding) cancelation

 so please identify what I measured.

(=What was I measuring? Electric potential?)

If you want people to diagnose your experiments, start a new thread. These are not the Millikan oil drop experiment. AC does not necessarily give the same results as DC.