Electric current is the rate of flow of electric charge through a conductor, such as a metallic wire. It is a scalar quantity that represents how much electric charge passes through a given point in a circuit per unit time.
Current is denoted by the symbol I, and its SI unit is the ampere (A).
⚛️ Electric Charge
Electric charge is a fundamental property of matter that causes it to experience a force in an electric field. It exists in two types:
Positive charge (associated with protons)
Negative charge (associated with electrons)
The SI unit of charge is the coulomb (C).One coulomb is the amount of charge carried by approximately 6.242 × 10¹⁸ electrons.
🔁 Relationship Between Current and Charge
The mathematical formula that relates electric current (I) and electric charge (Q) is:
I = Q / t
Where:
I is current in amperes (A)
Q is charge in coulombs (C)
t is time in seconds (s)
This formula tells us how much charge flows through a point in a circuit in a given time.
🧲 Flow of Electrons
In a conductor, electric current occurs due to the movement of free electrons.Electrons move from the negative terminal of a battery to the positive terminal, but by convention, we say current flows from positive to negative.
This electron flow is typically random in the absence of a voltage, but under an electric field (such as from a battery), the electrons gain a net drift in one direction.
🔍 Measuring Electric Current
To measure electric current in a circuit, we use special instruments that detect and measure how much current is flowing.
⚙️ Galvanometer
A galvanometer is a very sensitive instrument used to detect small electric currents.It operates based on the interaction between electric current and magnetic fields. When current passes through a coil inside the device, it experiences a torque that deflects a needle.Galvanometers are mostly used in laboratories for detection, not full measurements.
⚙️ Ammeter
An ammeter is an instrument used to measure the electric current flowing through a circuit.It is connected in series with the circuit element so that the same current passes through it.
Ammeter is a modified galvanometer that can measure larger currents by reducing its sensitivity and increasing its current-handling capacity.
⚡ Ampere (Amp)
The ampere (A) is the SI unit of electric current.One ampere is defined as the flow of one coulomb of charge per second.
1 A = 1 C/s
In simple terms, if 6.242 × 10¹⁸ electrons flow past a point in one second, that's 1 ampere of current.
These concepts are foundational in the study of electricity, and understanding them deeply helps in grasping how electric circuits function, how current behaves, and how it is measured in practical and experimental physics.
