Measuring the potential of the atmosphere

[quasar987]

In lecture 9 of the second volume of the Feynman Lectures on physics, it is written...

How can we measure [the field in the air above the ground] if the field is changed by putting something there? There are several ways. One way is to place an insulated conductor at some distance above the ground and leave it there until it is at the same potential as the air. If we leave it there long enough, the very small conductivity in the air will let the charges leak off (or onto) the conductor until it comes to the potential at its level. Then bring it back to the ground, and measure the shift of its potential as we do so.

I don't understand the procedure he describes. Firstly, what is an insulated conductor?

The continues to describe another method:

A faster way is to let the conductor be a bucket of water with a small leak. As the water drops out, it carries away any excess charges and the bucket will approach the same potential as the air. (The charges as you know, reside on the surface, and as the drops come off "pieces of surface" break off.) We can measure the potential of the bucket with an electrometer.

What "excess charges" is he talking about"? Will the bucket become progressively electrically charged as the water escape?

 

[krab]

Insulated conductor is a conductor that is not connected by another conductor to anything else.

Any time there is a potential difference between two conductors there are excess charges. When you connect the two together, charges flow from one to the other until the potential difference is zero.

 

[charng]

I would like to clarify and expand upon the methods described in the lecture. An insulated conductor is a material, such as metal, that does not allow electricity to flow through it easily. This allows the conductor to maintain its own charge without leaking it into the surrounding environment.

In the first method described, the insulated conductor is placed at a distance above the ground for a period of time to allow any excess charges in the air to dissipate. Once the conductor reaches the same potential as the air, it is brought back to the ground and the potential shift is measured. This method relies on the small conductivity of air to slowly transfer any excess charges to the conductor.

The second method described involves using a bucket of water as the insulated conductor. As the water leaks out of the bucket, it carries away any excess charges in the air, causing the bucket to approach the same potential as the air. The excess charges referred to in the lecture are any unbalanced charges in the air that may affect the potential measurement.

It is important to note that the bucket does not become electrically charged as the water leaks out. Instead, the charges in the air are neutralized by the water, causing the potential to decrease. The bucket itself maintains a neutral charge.

In conclusion, these methods demonstrate ways to measure the potential of the atmosphere by utilizing the properties of an insulated conductor and the conductivity of air. It is important to carefully control and monitor the conditions in order to obtain accurate measurements.