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Kirchhoff's first law and Kirchhoff's Second law

 Kirchhoff's first law 


  • the algebraic sum of the currents meeting at a junction in a closed electric circuit is zero,          i.e.,  𝜮I= 0
  • Consider a junction O in the electrical circuit at which the five conductors are meeting. Let I1, I2,  I3,  I4, and Ibe the currents in these conductors in directions,  
  • Let us adopt the following sign convention the current flowing in a conductor towards the junction is taken as positive and the current flowing away from the junction is taken as negative.
  • According to Kirchhoff's first law, at junction O                                                                  
               



                 (-I1 ) + (-I2 ) + I + (-I4 ) + I = 0
                or -I1  +  -I+ I3  -I4  + I5 = 0
                or  𝜮I = 0
  • I3  + I5 = I1 + I+ I4   i.e., the total current flowing towards the junction is equal to the total current flowing out of the junction.
  • Current cannot be stored at a junction. That is, there is no point/ junction in a circuit that can act as a source or sink of charge. 
  • Kirchhoff's first law supports the law of conservation of charge.


Kirchhoff's Second law  


  • The algebraic sum of changes in potential around any closed path of an electric circuit (or closed-loop) involving resistors and cells in the loop is zero, i.e.,  𝜮∆ V= 0.
  • In a closed loop, the algebraic sum of the EMFs and algebraic sum of the products of current and resistance in the various arms of the loop is zero, i.e., 𝜮ε   + 𝜮 IR  = 0.
  • Kirchhoff's second law supports the law of conservation of energy, i.e., the net change in the energy of a charge, after the charge completes a closed path must be zero.
  • Kirchhoff's second law follows from the fact that the electrostatic force is a conservative force and work done by it in any closed path is zero.
  • Traverse a closed path of a circuit once completely in a clockwise or anticlockwise direction.


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