Electric Current

• Electric current is a basic concept of electricity and describes the flow of electric charge through a conductor.
• In daily life, electric current is involved in the working of bulbs, fans, chargers, mobile devices, and household wiring.
• A steady electric current is observed in circuits where charges move continuously through a closed conducting path.

• The unit of electric current, ampere, is named after the French scientist André-Marie Ampère.
• Ampère carried out important experiments in electricity, and his work helped establish methods for understanding and measuring electric current.
• The visible source material includes this historical note as supporting background rather than as the main concept.

Current is defined as the rate of flow of charge.

A continuous and closed path of an electric current is called an electric circuit.

I = \[\frac {Q}{t}\]

Where:

• I = electric current
• Q = charge flowing through the conductor
• t = time taken

SI unit of current = ampere (A).

1. Explanation

• Electric current is produced when electric charges flow through a conductor.
• In metallic conductors, electrons are the charge carriers.
• Current exists only when there is a closed circuit.

2. Electric Circuit

• A circuit must be continuous and closed for current to flow.
• If the switch is open or the circuit is broken, current stops flowing, and electrical devices stop working.

3. Direction of Current

• Electrons move from the negative terminal to the positive terminal.
• By convention, current is taken to flow from the positive terminal to the negative terminal in the external circuit.
• Therefore, conventional current is opposite to electron flow.

4. Important facts

• Charge on one electron is approximately 1.6 × 10^-19 C.
• Small currents are expressed as: 1 mA = 10^-3 A and 1 μA = 10^-6 A.
• The source material also presents current as a useful quantity for describing charge flow in circuits and devices.

5. Quick process view

• Charge moves through a conductor.
• Movement occurs through a closed path called an electric circuit.
• The amount of charge passing per unit time gives the current.
• Current is measured in amperes.

• Conventional current is defined as the direction in which positive charge would flow — from the positive terminal to the negative terminal in the external circuit.
• This convention was set by Benjamin Franklin (1752), before the electron was discovered.
• Electron flow is the actual movement of electrons, from the negative terminal to the positive terminal, since electrons are negatively charged and are attracted toward the positive terminal.
• J.J. Thomson discovered the electron in 1897, revealing that actual charge carriers move opposite to the conventional direction.
• Circuit calculations give identical results whether conventional flow or electron flow is used, so both conventions remain valid in practice.

Charge carriers are the particles responsible for carrying electric charge and producing current in a medium.

• Metals: Free (valence) electrons act as charge carriers, forming a "sea" of mobile electrons within the metal lattice.
• Electrolytes (e.g., salt solutions): Both positive ions (cations) and negative ions (anions) act as charge carriers, moving toward oppositely charged electrodes.
• Ionised gases (plasma): Free electrons and positive ions serve as charge carriers once the gas is ionised under high potential.
• Semiconductors: Free electrons and holes act as charge carriers.
• In a vacuum, free electrons themselves can act as charge carriers.

• RMS value of AC is defined as the square root of the mean of the squares of the instantaneous current values over one cycle.

• Electric current flows only when the circuit forms a complete (closed) loop from one terminal of the source, through the components, and back to the other terminal.
• A switch is used to make (close) or break (open) this loop:
  Switch ON (closed circuit) → current flows, connected devices operate.
  Switch OFF (open circuit) → no current flows, devices stop working.
• This is a foundational Class 10-level concept usually paired with circuit diagrams showing cell, switch, and load (e.g., a bulb).

Question: A charge of 30 C flows through a wire in 2 minutes. Find the current. 

Solution: Given, Q = 30 C
Time, t = 2 min = 120 s

Using I = \[\frac {Q}{t}\],

Answer: 0.25 A.

Question: A current of 0.5 A flows through a bulb for 10 minutes. Find the charge passed. 

Solution: Given, I = 0.5 A
Time, t = 10 min = 600 s

Using Q = It,

Answer: 300 C.

• Electric current is used in lighting devices such as bulbs and torches.
• Household appliances work only when current flows through a complete circuit.
• Very small currents are important in electronic circuits, sensors, and mobile devices.
• Lightning is also an example of a large-scale movement of electric charges mentioned in the source references.

• Electricity is a convenient and controllable form of energy widely used in homes, industries, schools, and hospitals.
• Electric current is produced when electric charges flow through a conductor, and it flows only through a closed, continuous electric circuit.
• A switch completes or breaks the circuit; when the circuit is broken, current stops flowing, and devices like bulbs do not glow.
• Electric current is the rate of flow of charge, given by the relation I = Q / t, where Q is charge and t is time.
• In metallic wires, electrons are the charge carriers, but by convention, current flows from the positive to the negative terminal, in the opposite direction to electron flow.