## 09/01/2018

### Charge and Current The law of conservation of energy states that the charge can neither created nor destroyed, it can only transferable from one place to another place.  Therefore the algebraic sum of all charge in an electrical circuit is equal to zero.  The electrical charge is mobile therefore it can be transferred to one place to another.  The positive charge moves in one direction whereas the negative charge moves in the other direction.  The motion of electrical charge creates electrical current in a closed circuit.  The Benjamin Franklin invented that the conventional direction of electrical current is opposite to negative charge or electron.  There is a following relation between charge and current                   i = dq / dt                  q = ∫ i dt

Direct Current ( DC ) or Direct voltage
• If the magnitude of current or voltage does not change with time, it is called as direct current.
• The magnitude of direct voltage and current remains constant with respect to time.

Alternating Current ( AC )  or Alternating voltage
• If the magnitude of current or voltage changes sinusoidal with time, it is called as alternating current.
• The alternating supply may be single phase or three phase.

### Voltage or Potential It is defined as the work done in bringing a positive charge of one coulomb from infinity to that point against magnetic field.  The potential is equal to work done per unit charge.  The earth is taken as reference potential zero because the potential of earth remains constant in spite of it keeps and losing charge.        One voltage = Work done / Charge                            = Joule / Coulomb EMF ( Electro – Motive Force ) It is force that requires moving electrons to produce an electrical current. It is better known as EMF or battery source.  It is measured in voltage.  The word force is used for electrical potential not for mechanical force.                                       OR It is source of energy that causes electrical current to flow in the given closed circuit. Potential Difference It is defined as potential difference of one voltage between two points if one joule of work is done for shifting a point charge from one point to other point.  The potential difference between two points is considered by considering one point as reference potential.  Let us consider that the potential of point is + 10 V as compared to potential of point B. Similarly the potential of point P is – 10 V as compared to potential of point Q. 