Resistor

What is Resistor ?

100k/2W  Resistor

A resistor is a component of an electrical circuit that resists the flow of electrical current. A resistor has two terminals across which electricity must pass, and is designed to drop the voltage of the current as it flows from one terminal to the next. A resistor is primarily used to create and maintain a known safe current within an electrical component.

Also see  Conductor,Semiconductor   Resistor color code,  Capacitor color code

What is resistance ?

Resistance is the opposition that a substance offers to the flow of electric current.  It is represented by the letter R.  The standard unit of resistance is the ohm, sometimes written out as a word, and sometimes symbolized by the Greek letter omega.  When an electric current of one ampere passes through a component across which a potential difference (voltage) of one volt exists, then the resistance of that component is one ohm.

Combination of Resistor

When a number of resistors are to be used together in a combination, it is known as “combination of resistors”. All these resistors combined together behave like a single resistor, called the “equivalent resistor, which maintains the same current or the same potential difference of the circuit as before. Resistors can be combined in two ways: a) Series combination,b) Parallel combination 

Series Combination: A number of resistors are said to be connected in series if they are connected end to end consecutively ( See Fig. 1 ) so that the same current flows through each. In connection with the series combination of resistors, the following points are to be noted:

Fig. 1     Series Resistor

1. Current is same through all the resistors.
2. Total p.d=sum of individual p.d’s across the individual resistors.
3. Individual p.d is directly proportional to the individual resistances of the resistors.
4. Total resistance of the combination is greater than the greatest individual resistance.
5. Total resistance of the combination= sum of the resistances of the individual resistors. 

Example : 

A resistor of 120k,100k and 80k are connected in series then what is the total resistance?  

R=r1+r2+r3, R=120k+100k+80k   so R=300k

Parallel Combination: A number of resistors are said to be connected in parallel when they are placed side by side and their corresponding ends joined together ( See Fig. 2 ) so that the main current is distributed among them. In connection with parallel combination of resistors, the following points are to be noted:

Fig. 2   Parallel Resistor

1.  P.D across each resistor is the same.
2.  Total current= sum of currents passing through individual resistors.
3.  Individual currents are inversely proportional to individual resistances.
4.  Equivalent resistance of the combination is less than the smallest individual resistance
5. Reciprocal of the equivalent resistance is the sum of the reciprocals of individual resistances.                        

Example : 

A resistor of 120k,120k and 120k are connected in parallel then what is the total resistance?  

1/R=1/r1+1/r2+1/r3

      

 

       1/R=3/120k      Total R=40K

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Q & A

1. What is capacitor?
2. What is VDR, LDR, MFR, CFR?
3. What is Thermistor?

Also see:
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Epabx Programming Manual
Free Crystal Epabx software
Circuits diagram