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Ohm's Law

  What is meant by  potential difference ?
As we mentioned before to understand a scientific topic we make modeling for this topic

So to understand what is the voltage (or the potential difference), we will use this model.
This is an animation of a series circuit where electrical energy is shown as gravitational potential energy. The greater the change in height, the more energy is used or the more work is done.

this animation you should notice the following things:

  • The battery or source is represented by an escalator which raises charges to a higher level of energy.
  • As the charges move through the resistors (represented by the paddle wheels) they do work on the resistor and as a result, they lose electrical energy.
  • The charges do more work (give up more electrical energy) as they pass through the larger resistor.
  • By the time each charge makes it back to the battery, it has lost all the energy given to it by the battery.
  • The total of the potential drops across the resistors is the same as the potential rise across the battery. This demonstrates that a charge can only do as much work as was done on it by the battery.
  • The charges are positive so this is a representation of Conventional Current (the apparent flow of positive charges)
  • The charges are only flowing in one direction so this would be considered direct current ( D.C. ).
We measure the potential difference with volts (v) by using a voltmeter.  

 The electric potential difference between two points on a circuit (ΔV) is equivalent to the product of the current between those two points (I) and the total resistance of all electrical devices present between those two points (R). Often referred to as the Ohm's law equation, this equation is a powerful predictor of the relationship between potential difference, current and resistance.

Suppose a resistance having a value of R ohms carries a current of I amperes. Then the voltage across the resistor is equal to the product IR.    V = I x R
Ohm's law

      You can have better understanding for Ohm's law from this 
interactive resource which combines the actual experiment
 with the algebraic relationship.