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XII CLASS PHYSICS UNIT 2 TOPICS

   unit 2 electric current & ohm's law     page1





Electric current: the rate of flow of change through any cross section of a conductor is called electric current.


Electric current=charge/time


 if charge q flows through a wire in time t,  then I=q/t
if charge dq flows through a wire in time dt, then I=dq/dt


Direction of current: As electron move lower potential to higher potential.

example: water flow from a higher level to lower level. therefore conventionally, the direction of current is taken along the direction of +ve charge know as conventional current.

the direction of flow of electrons gives the direction of electronic current which is opposite to the magnitude and direction.

electric current has both magnitude and direction ,but it is not a vector quantity,  because law of vector addition is not valid to add the current

S. I unit :  s.i unit for current is coulomb per second which is called ampere (A).


Ohm's law :
ohm's law stated that if physical condition such as temperature, strain etc remains same,  then electric current flowing through a conductor is always directly proportional to the difference applied across it.


if a potential difference Via is applied across a conductor, a current Iflows through it . then  V{ I Or V=RI.

where R is constant called resistance of conductor 
it's depends upon: 

  1. nature of material of conductor 
  2. shape & size of conductor 
  3. physical condition of the conductor
It doesn't depend on V& I a graph between V & I is a straight line
   


graph b/w I&V     

                                                                                            

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