# Calibrating a metal leaf or pith ball electroscope

• Electrical
• TJonline
In summary, the conversation is about building a DIY metal leaf or pith ball electroscope with a circular arc voltage scale visible behind the deflected ends of the leaves. The goal is to calibrate the scale using the equations of deflection and measurements of charge density, weight, thickness, and area or volume. The voltage will be determined using a cheap, high-voltage, step-up, transformer-terminated electrostatic generator module or a Van der Graff generator. The equation C = Q / V = e A / d is mentioned, but the capacitor equation does not apply in this case as one plate is the two leaves with identical charge and the other is Earth ground. The conversation also mentions alternative instruments such as electrostatic voltmeters
TJonline
TL;DR Summary
Trying to calculate the charge density upon the leaves as a function of voltage applied to a DIY metal leaf or pith ball electroscope without knowing the voltage applied (relative to earth ground) beforehand.
I'm trying to build a DIY metal leaf or pith ball electroscope. I want to provide it with a circular arc voltage scale visible directly behind the (deflected) ends of the leaves. To calibrate the scale with ballpark accuracy, I want to determine the charge density upon the leaf pair (or pith balls), measure their weight, thickness and area (or volume) and apply the equations of deflection (of the pith balls):

Or a hairier integral as to two leaves deflecting at varying angles. Ultimately, I want to determine the voltage applied to it (relative to Earth ground) provided by a cheap, high-voltage, step-up, transformer-terminated (and earth-grounded output terminal), electrostatic generator module (or Van der Graff generator) without buying an expensive electroscope and measuring the voltage that way to calibrate the circular arc scale. I'm aware of the equation: C = Q / V = e A / d = e0 er h w / d, where e0, er, h, w and d are permeability of free space, relative permeability, plate height, width and distance between plates. But in this case, one plate is the two leaves (or pith balls) with identical (repulsive) charge and the matching plate is Earth ground an 'infinite' distance away. Capacitance C goes to zero as d goes to infinity, and thus so does charge C, according to the capacitor equation. It's not really a capacitor per se. But the leaves have a charge obviously. Can't seem to find the physics/engineering information that I need to determine the charge and voltage (both being unknowns). The capacitor equation always comes up when I search on 'plates', 'charge', 'voltage', 'electroscope', etc. Any ideas? Or is that too vague?

Oops! Me so stupid. If those modules are terminated by a transformer, then all that can come out is pure AC. Which is not electrostatic. So, make that either a Van der Graff generator or some silk cloth rubbed on a glass rod.

## 1. How do I calibrate a metal leaf electroscope?

To calibrate a metal leaf electroscope, you will need a known source of charge, such as a charged rod or a battery. First, discharge the electroscope by touching the metal ball or plate with your finger. Then, bring the charged source near the metal ball or plate without touching it. If the leaves of the electroscope diverge, the electroscope is properly calibrated. If the leaves do not move, adjust the position of the charged source until the leaves move. Finally, record the angle of divergence to use as a reference for future measurements.

## 2. Can I use any type of charged source for calibration?

Yes, you can use any known source of charge for calibration. This can include a charged rod, a battery, or even a Van de Graaff generator. The important thing is to make sure that the source is known to have a specific charge, so that you can accurately calibrate the electroscope.

## 3. How often should I calibrate my metal leaf electroscope?

It is recommended to calibrate your metal leaf electroscope before each use. This will ensure that your measurements are accurate and reliable. If you plan on conducting a series of experiments, it may be helpful to calibrate the electroscope at the beginning of each experiment.

## 4. What is the purpose of calibrating a metal leaf electroscope?

The purpose of calibrating a metal leaf electroscope is to establish a known reference point for future measurements. This allows for more accurate and reliable readings when conducting experiments or making observations about the presence and magnitude of electric charge.

## 5. Can I calibrate a metal leaf electroscope without a known source of charge?

No, it is not possible to accurately calibrate a metal leaf electroscope without a known source of charge. Without a reference point, the electroscope readings will not be reliable. It is important to have a known source of charge for calibration in order to ensure accurate measurements.

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