Electric charge is a physical property of matter that causes it to experience a force when placed in an electromagnetic field. It is measured using a unit called coulomb (C) which is defined as the amount of charge that passes through a given point in an electric circuit in one second when the current is one ampere.
The instrument used to measure electric charge is called an electrometer. It is a sensitive device that can detect and measure very small amounts of charge. There are different types of electrometers such as the gold-leaf electroscope, the quadrant electrometer, and the picoammeter, each with different levels of sensitivity and accuracy.
In a circuit, electric charge is measured using an ammeter. An ammeter is connected in series with the circuit and is used to measure the flow of electric current, which is directly proportional to the amount of charge passing through the circuit. The ammeter measures the charge in coulombs per second (C/s) or amperes (A).
In a static object, electric charge is measured using an electroscope. An electroscope is a device that uses the principle of repulsion between like charges to determine the presence and magnitude of an electric charge. The electroscope consists of a metal rod with two thin metal leaves at the bottom, and when a charged object is brought near it, the leaves will either repel or attract each other, indicating the presence and type of charge.
Positive and negative electric charges are two types of electric charge that exist in nature. Positive charge is associated with protons, while negative charge is associated with electrons. They have opposite properties and attract each other, while like charges repel. In terms of measurement, positive and negative charges are measured in the same units (coulombs), but have opposite signs (+ and -).