current | resistivity | Current electricity | ohm law | electric current | physics

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Current electricity and ohm's law(Current electricity) :-


•What is current?

Rate of flow of electric charge with time through any cross section of a wire is called current. It is denoted by I .
Thus if charge "dq" flows through a wire in small time "dt" then electric current through wire is given by :
                                            I=dq/dt 
1 ampere = 1coulomb/1 second 
1A=C/s

•Ampere :-                                                      

   The current Through a wire is called one ampere if one coulomb charge is flow through Any cross section of wire in one second 

•Ohm's law:-


Ohm’s principal discovery was that the amount of electric current through a metal conductor in a circuit is directly proportional to the voltage impressed across it, for any given temperature. Ohm expressed his discovery in the form of a simple equation, describing how voltage, current, and resistance interrelate:

V=IR


•ohms law equation

In this algebraic expression, voltage (V) is equal to current (I) multiplied by resistance (R). Using algebra techniques, we can manipulate this equation into two variations, solving for I and for R, respectively:

I=V/R.                   R=V/I

ohms equation current resistance

•Resistance of a conductor :-               

V=IR

R=V/I  

The resistance of a conductor is defined as the opposition offered by a conductor to the flow of charge .
It is measured as a ratio of potential difference of the conductor to the current flowing through that conductor.
cause of resistance is the collision of free electrons against Ions

•Unit of resistance :-         

                          
SI unit of resistance is Ohm.
1ohm=1 volt/1ampere

Resistivity:-                                       

The resistivity of a substance is the resistance of a cube of that substance having edges of unit length, with the understanding that the current flows normal to opposite faces and is distributed uniformly over them.

The electrical resistivity is the electrical resistance per unit length and per unit of cross-sectional area at a specified temperature.
The SI unit of electrical resistivity is the ohm⋅metre (Ω⋅m). It is commonly represented by the Greek letter ρ, rho.

Although the SI resistivity unit, the ohms metre is generally used, sometimes figures will be seen described in terms of ohms centimetres, Ω⋅cm.


•Some important board exam level question answers :-


Q. 1) Define electric current  ?

Ans:- The rate of flow of charge through any cross section of a conductor is called electric current i.e charge per second. 


Q. 2) What is the unit of current  ? Define. 

Ans:- The unit of current is ampere. If 1 C charge flows through any cross section of a conductor in 1 s then the current flowing is said to be 1A .


Q. 3) State ohm's law ?

Ans:- Ohm's states that the physical conditions like temperature etc., remaining constant the potential difference across a conductor is directly proportional to the current flowing through it. 


Q. 4) Write mathematical formula for resistivity ?

Ans:- Resistivity is giving by
          ρ = RA/l 
Where R is the resistance, A is area of cross section and l is the length of given conductor. 


Q. 5) What is meant by resistivity of a conductor  ?

Ans:- Resistivity of a given material of a conductor is constant, it is the resistance offered by unit cube of the conductor. 


Q. 6) Does the resistance of a wire depend on the current flowing through it? 

Ans:- Resistances doesn't depend on current. 


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