PASSIVE ELEMENTS:
RESISTANCE:
It is the property of a material by which opposes the current the resistance of
the element denoted by the symbol 'R'.Resistance is represented by 'Ω'(ohm).The
resistance of a given material physical properties of the material is given
material physical properties of the material is given by,
R= P*l/a
where P
=Resistivity in Ω/m (or)Ω/cm (or) Ω/mm .
l= Length of the conductor in
cm (or) m (or) mm .
a= Cross sectional area of
the conductor in m^2 (or) cm^2 (or) mm^2 .
·
The relation between voltage and current for a
resistance is given by "ohm's law" .
V=iR , i=V/R , R=V/i ,
·
The power observed by the resistor is given by ,
P=Vi
=V*(V/R) =(V^2/R)=iR*i =i^2*R
P=Vi=V^2/R =i^2*R - watts.
The
energy of the resistor is given by W=Vit -
Joules
(or) V^2/R *t -Joules
(or) I^2 *Rt- Joules 
·
When we apply a voltage, V, between the
leads of a resistor we can expect a current, I=V/R to flow through it. The way the electrons
move through the solid material is a bit like the way a gas diffuses through a
sponge or toothpaste squeezes along a tube. The electrons keep being
accelerated by the applied electric field. This means they acquire some kinetic
energy as they move towards the +ve end of the piece of material. However,
before they get very far they collide with an atom and lose some of their
kinetic energy. This keeps happening. As a result they tend to ‘drift’ towards the +ve end, bouncing
around from atom to atom on the way. This process is illustrated in figure(b)
Here ,the Resistor value is depends on
the following properties:
1)It is directly proportional to the
length of the wire(or)conductor.
2)It is inversely proportional to cross
sectional area of the conductor.
3)Nature of the material.
4)Depends up on temperature.
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