RESISTANCE

RESISTANCE

Resistance:-

• The abstraction of current in a circuit this property are called resistance.

                                                                    or

•  To oppose the current flow , this is called resistance.
• Resistance is a scalar quantity.
• It is derive physical quantity.
• Its SI-Unit is "ohm".
• Dimension of resistance is

• TYPES OF RESISTANCE:-  There are different type of resistance, they are given bellow:-
• Fixed Resistance
• Carbon Resistance
• Metal film Resistance
• Ceramic Resistance
• LDR
• Thermistor
• Wire wound Resistance 
• Variable Resistance
• Fixed Resistance:-  The value of this resistance not changed after manufacturing. The symbol of this resistance is:-

                                            

• Carbon Resistance:- 
• It is most general proupse Cheep resistor.
• Tolerances of carbon resistor is plus & minus 5% or 10%.
• Practically tolerances of carbon resistor is plus & minus 5%.
• Disadvantage of carbon resistor is they tend to be electrically noise.
• In carbon resistor, Inert filler is "alumina".

                              

• Metal Film Resistor:-
• This resistor are used when higher tolerances.
• Metal film resistor much accrue value of carbon resistance.
• Its tolerances lies between plus & minus 1%to 2% .
• Practically tolerances of metal film  resistor is plus & minus 0.05%.
• Ni-chrome(Ni-Cr) is generally used for the material of metal film resistor. 
• In metal film resister Oh-mic range is 100 to 1 mega ohm. 
• Metal film resistor can be expected "lowest noise.
• Metal film resistor are evaporated using very low pressure. 
• In case of evaporated nichrome resistor resistance value is increase with time.  

                                           

• Ceramic Resistor:- 
• They have very high power rating.
• This  Resistor can become extremely hot when used for high power application.

• LDR:-
• LDR stand for "light dependent resistor".
• It is made of "Cadmium Sulfide" Photo cell.
• It resistor depends on the amount of light falling its.
• It kept in darkness than the value resistance will be "high".
• It kept in more lights than the value resistance will be "low"   

                                  

• Thermistor:-
• This resistor depends on temperature.
• thermistor are two types NTC & PTC.
• NTC stand for negative temperature coefficient.
• PTC stand for positive temperature coefficient.
• NTC thermistor , temperature will be increase than resistance will be decrease.
• PTC thermistor , temperature will be increase than resistance will be increase.
• It is used for temperature censer.  

                                         

• Wire Wound Resistor:-
• It is made of metal resistance wire.
• It is high wattage resistor.
• In this resistor using thick wire material.
• This resistor not be used for high frequency circuit.

                              

• Variable resistor:-
• Variable resistor are also called rheostat.
• Some variable resistor must be tuned many  time(multi tum pot).
• It is to use the whole range of resistance they offer.
• This allows very precise adjustment of this value.
• This is also called  "Potentiometer"  or "Trimmer Potentiometer " or "Presets".
• Maximum rotation angle of variable resistor is 300 degree.
• Variable resistor made of "Concentain wire" .