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6.2 What is Voltage?

Description:


  • The electrons in a conductor (copper for example) freely move from atom to atom, but in a completely random way. 
  • Motion of free electrons is normally haphazard. So, a sort of pressure or push helps electrons to move in a particular direction. 
  • The technical term for this pressure or push is electromotive force, EMF for short or sometimes simply E. It creates pressure on the electrons which channelizes them to flow in a single direction. But you know it more commonly as voltage.

Voltage:

  • Voltage (V) is the unit of potential difference. More clearly, voltage is the difference in potential, between two points. 
  • Basically, to find the difference, we need two points. Similarly, to measure volt we need two points. Let A and B are the two points connected through any conducting material.

  • Potential of A is 50 and B is 30 and the unit of potential is coulomb (Q). ‘Point A’ has high potential which means more electrons. ‘Point B’ has low potential which means less electrons. And the difference between these two points is the Voltage. In this case 50 Q – 30 Q = 20 V
  • As the points are connected with a conductor such as a copper wire, that forms a circuit through which electric current will flow. 
  • This current continues to flow until all the extra negative charges on the negative side of the circuit have moved to the positive side. When that has happened, both sides of the circuit become electrically neutral and the current stops flowing.


Current:

Scenario 1: 50 Q – 30 Q = 20 V

Scenario 2: 50 Q – 50 Q = 0 V

i.e., difference between 50 coulomb and 30 coulomb is 20 volts but when there is equal potential at both the points, then there is zero volt which means no current. Thus, voltage creates the potential for current to flow. If current can be compared to the flow of water through a hose, voltage can be compared to water pressure at the faucet. It’s water pressure that causes the water to flow in the hose.

Flow of electrons from high potential (A) to low potential (B) at a particular point per second is the current(I) measured in Ampere(A) or in other words Charges (coulomb) crossing through point C per second is the ampere. 

Ampere (A) = 1 Coulomb1 Second

If five units passes through point C for one second the its 5 Ampere.


Just few extra Information:

  • Conventional current flow means that current flows from positive to negative. Thus, the current flows from the positive terminal of the battery through the lamp and then back to the negative terminal of the battery. 
  • In reality, conventional current flow is opposite of the actual flow of electrons through the circuit. The negative side of the battery has an excess of negatively charged particles (extra electrons / high potential) whereas the positive side has an excess of positively charged particles (missing electrons). Thus, the electric charge flows through the conductor from the negative side of the battery, through the lamp, and back to the positive side.


Pre-requisites for the current to flow in a conductor:

  • Circuit needs energy source (battery for instance) that produces voltage.
  • Without voltage, (pressure) electrons flow randomly and undirected, hence current cannot flow.
  • Voltage creates pressure on the electrons which channelizes them to flow in a single direction


Read the next post: 6.3 What is Resistor? 

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