Current Electricity

Current Electricity for JEE & NEET

Electric Current

  • Definition: Electric current (I) is the rate of flow of electric charge (Q) through a conductor.
    • I = dQ/dt
  • Unit: The SI unit of current is the ampere (A), where 1 A = 1 C/s (coulomb per second).
  • Charge Carriers: In conductors, the charge carriers are typically electrons. In electrolytes, they are ions. In semiconductors, both electrons and holes contribute to current.
  • Direction: Conventional current flows from the positive terminal of a battery to the negative terminal, although electrons actually flow in the opposite direction.

Ohm’s Law

Ohm’s law describes the relationship between current, voltage, and resistance:

  • Statement: The current (I) flowing through a conductor is directly proportional to the potential difference (V) across it, provided the temperature and other physical conditions remain constant. 
  • Formula: V = IR
  • Resistance (R): Resistance is the opposition to the flow of current. Its SI unit is the ohm (Ω).

Resistors

  • Function: Resistors are components designed to provide a specific resistance in a circuit.
  • Types: There are various types of resistors, including carbon resistors, wire-wound resistors, and metal film resistors.
  • Colour Code: Resistors often have coloured bands that indicate their resistance value.
  • Combinations:
    • Series: When resistors are connected in series, the total resistance is the sum of the individual resistances.
    • Parallel: When resistors are connected in parallel, the reciprocal of the total resistance is the sum of the reciprocals of the individual resistances. 

Electrical Circuits

  • Definition: An electrical circuit is a closed path through which current can flow.
  • Components: Circuits typically include a voltage source (e.g., battery), conductors (e.g., wires), and load (e.g., light bulb, motor).
  • Circuit Diagrams: Circuit diagrams use standardized symbols to represent circuit components and their connections.
  • Kirchhoff’s Laws:
    • Kirchhoff‘s Current Law (KCL): The sum of currents entering a junction is equal to the sum of currents leaving the junction. 
    • Kirchhoff’s Voltage Law (KVL): The sum of the potential differences around any closed loop in a circuit is zero. 

Electric Power

  • Definition: Electric power (P) is the rate at which electrical energy is consumed or dissipated.
  • Formula: P = VI = I²R = V²/R
  • Unit: The SI unit of power is the watt (W), where 1 W = 1 J/s (joule per second).

Heating Effects of Current

  • Joule’s Law: When current flows through a resistor, electrical energy is converted into heat energy. The amount of heat produced is given by:
    • H = I²Rt where:
      • H is the heat energy (in joules)
      • I is the current (in amperes)
      • R is the resistance (in ohms)
      • t is the time (in seconds)
  • Applications: Electric heaters, fuses, and many other devices utilize the heating effect of current.

Cells and Batteries

  • Cell: A cell is a device that converts chemical energy into electrical energy.
  • Battery: A battery is a combination of two or more cells.
  • Types: Primary cells (non-rechargeable) and secondary cells (rechargeable).
  • Electromotive Force (EMF): The EMF of a cell is the potential difference across its terminals when no current is flowing.

Additional Current Electricity Concepts for JEE & NEET

  • Drift Velocity: The average velocity of charge carriers in a conductor under the influence of an electric field.
  • Electrical Conductivity: A measure of a material’s ability to conduct electric current.
  • Superconductivity: A phenomenon in which certain materials exhibit zero resistance below a critical temperature.

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