Physics

• Electric Current: The flow of electric charge, measured in Amperes (A).
  
  

• Conductors: Materials that allow charge carriers, usually electrons, to flow freely.
  
  

• Ohm's Law: This law states that the current (
  $I$
  ) through a conductor is proportional to the voltage (
  $V$
  ) across it, provided that resistance (
  $R$
  ) is constant:
  $I = \frac{V}{R}$.
  
  

• Resistivity: A property of materials that indicates how much they resist the flow of current, denoted by the Greek letter
  $\rho$.
  
  

• Limitations of Ohm's Law: This law does not apply to all materials, especially those that are non-linear or at very high voltages or frequencies.
  
  

• Materials' Resistivity: Different materials resist current differently; good conductors (like copper) have low resistivity, whereas insulators (like rubber) have high resistivity.
  
  

• Temperature and Resistivity: Generally, the resistivity of conductors increases with temperature, while for semiconductors, it decreases with temperature.
  
  

• Electrical Power: Power can be computed using the formula:
  $P = IV$
  , where
  $P$
  is power (in watts),
  $I$
  is current (in amperes), and
  $V$
  is voltage (in volts).
  
  

• Cells and EMF: A cell generates electric energy; EMF (Electromotive Force) is the potential difference when no current flows.
  
  

• Connections:
  
  

  • Series: In a series connection, total voltage is the sum of individual cell voltages, but the current remains the same.
    
    

  • Parallel: In a parallel connection, the total voltage across cells equals the voltage of one cell, while the total current is the sum of individual currents.
    
    

• Kirchhoff's Rules:
  
  

  1. Kirchhoff's Current Law (KCL): The total current entering a junction equals the total current leaving.
     
     

  2. Kirchhoff's Voltage Law (KVL): The sum of electrical potential differences in any closed circuit is zero.
     
     

• Wheatstone Bridge: A circuit used to accurately measure an unknown resistance by balancing two legs of a bridge.

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