# Understanding Charge Measurements

• physics369
In summary, the conversation discusses the difference between four measurements of charge: the charge of an electron, the relative charge of an electron, the elementary charge of an electron, and specific charge. The units for these measurements are specified, with the exception of the relative charge and the elementary charge, which are stated in terms of the proton's electric charge and the electron's electric charge. The importance of specifying units for numerical values is emphasized.
physics369
Hi,

Sorry if I have posted this in the wrong place. I'm having trouble understanding the difference between these four measurements of charge. Specifically whether the -/+ sign is important and what the unit is:

For example,

The charge of an electron is -1.602176487(40)×10^-19 coulombs, right?

The relative charge of an electron is -1, right? Because to get the relative charge you divide by the charge of an electron and, because it's negative, you add a - sign, right? Has this got a unit?

The elementary charge of an electron is the same as the charge, but because it's absolutely charge, the signs (-/+) are irrelevant, right? Is this also measured in coulombs?

For specific charge, you use the elementary charge and divide that by the mass, right? So for an electron it would be 1.60x10^-19 / 9.11 x 10-31. giving you 1.76x10^11 Ckg-1, right?

Any help/guidance would be much appreciated. :)

I wouldn't get hung up on the terminology (some of which is new to me). The important thing is to specify the units with any numerical value. Units are present for your first and fourth examples. For the second and third, I would say that the electron's electric charge is -1 in units of the proton's electric charge, or +1 in units of the electron's electric charge.

## 1. What is charge and why is it important to measure?

Charge is a fundamental property of matter that describes how objects interact with each other through the electromagnetic force. It is important to measure because it helps us understand and predict the behavior of electric and magnetic fields, which are crucial in many technological applications such as electronics and power generation.

## 2. How is charge measured?

Charge is typically measured using an instrument called an electrometer, which can detect and measure the amount of charge present on an object. This is usually done by measuring the electric current that flows through a circuit when a known voltage is applied to the object.

## 3. What are the units of charge measurement?

The SI unit of charge is the coulomb (C), named after the French physicist Charles-Augustin de Coulomb. Other common units of charge include the ampere-hour (Ah) and the milliampere-hour (mAh), which are often used to measure the charge of batteries.

## 4. How is charge measured in different materials?

Charge can be measured in different materials using various techniques, depending on the material's properties. For example, in conductors, charge can be measured by applying a voltage and measuring the resulting current. In insulators, charge can be measured using a device called a Faraday cup, which collects and measures the amount of charge deposited on its surface.

## 5. What are some common sources of error in charge measurements?

Some common sources of error in charge measurements include external electromagnetic interference, leakage currents, and errors in instrument calibration. It is important to carefully control and account for these factors to ensure accurate and reliable charge measurements.

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