Current


Current is nothing but flow of electrons from higher potential to lower potential.
An electric current is a stream of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is measured as the net rate of flow of electric charge through a surface or into a control volume.The moving particles are called charge carriers, which may be one of several types of particles, depending on the conductor. In electric circuits the charge carriers are often electrons moving through a wire. In semiconductors they can be electrons or holes. In a electrolyte the charge carriers are ions, while in plasma, an ionized gas, they are ions and electrons.

                                         

The SI unit of electric current is the ampere, or amp, which is the flow of electric charge across a surface at the rate of one coulomb per second. 
Mathematically, Current
                            I=Q/t 
                              or 
                          I=dq/dt 
The ampere (symbol: A) is an SI base unit. Electric current is measured using a device called an ammeter.

  • Electric currents create magnetic fields, which are used in motors, generators, inductors, and transformers.
  • In ordinary conductors, they cause Joule heating, which creates light in incandescent light bulbs.
  • Time-varying currents emit electromagnetic waves, which are used in telecommunications to broadcast information.
Ohm’s law, description of the relationship between current, voltage, and resistance. The amount of steady current(I) through a large number of materials is directly proportional to the potential difference or voltage(v) across the materials.
So, according to ohm's law Voltage
                                                            V∝I
                                                            V=IR 
                                                                     
where,  V= Voltage,
             I = Current, 
             R= Resistance
Mathematically Ohm's law is written as V/I=R or V=IR.

Voltage

Actually the word 'potential' refers to the ability to do some work. So, consider a unit charge (may be positive or negative) is present in an electric field. Now if the charge is positive then a force exerted on it and if the charge is moving towards the field, then both of the forces will be acting in the same direction which is analogical with a mass influenced by the gravity. On the other hand if the charge is negative and is moving in the electric field then this movement will be against the force of the electric field.
So we can see that in both the cases work is done (both positive and negative). This work done by the charge while moving in an electric field can be termed as electric potential.
Voltage is also called as a Electric Potential Difference.
So, Voltage, electric potential difference, electromotive force (emf), electric pressure or electric tension is the difference in electric potential between two points, which (in a static electric field) is defined as the work needed per unit of charge to move a test charge between the two points. 
More conventionally the definition of electric potential can be given as the work done needed to move a charge particle from one point to another point in the presence of an electric field. The potential is measured between the two points. The unit of representing electric potential is volt.
It is measured in volts and denoted as V. Voltage is either alternating current (ac) voltage or direct current (dc) voltage.
Alternating current voltage represented on a digital multi-meter by .
Direct current voltage represented on a digital multi-meter by and .

Volt can be expressed as the potential difference between two points in an electric circuit that imparts one joule (J) of energy per coulomb (C) of charge that passes through the circuit.

So, V=1 joule of energy/1 coulomb of charge
       V= W/Q 
           or
       V=dW/dq 


Power

The rate of change of energy is called Power.
In mathematical form
Power P=dW/dt

and we know that Voltage V=dW/dq and Current I=dq/dt

so, if we multiply and divide above equation with dq we get new equation 
P = dw/dt =(dW/dq)*(dq/dt)
P=V*I

So, we can say that power is a multiplication of Voltage and Current(P=VI)

we know that ohm's low stats that V=IR.
now put V=IR in P=VI we get P=(IR)I
P=I²R