Method of substitution for measurement of medium resistance

Method of substitution

Method of substitution

E= External battery

R= resistance to be measured

S= Variable resistance

R= Turning resistance

Sw= Switch

A= Amperemeter

The position of the switch is at a point 2 with the battery E makes a close loop with resistance r, ammeter and the unknown resistance R.

There will be a deflection of ampere meter.

The deflection an ammeter can be seen on the dial.

If the ampere meter reading is not readable it can be adjusted with the help of turning resistance r to be readable value.

Change the position of the switch to point 1. In this situation the position of the pointer in ammeter will be definitely different as resistance value of S and R are different, as the resistance value of r and R are different.

Adjust the value of variable resistance S in such a way that the pointer of ammeter rests to them previously observed value of the ammeter.

Remove the resistance S, check the value S. This resistance value of S is similar to equal to the value of R.


  1. This method is simpler.
  2. Circuit complexity is less.
  3. Medium value of resistance can be measured.


  1. Low value of resistance can’t be measured because it becomes negligible.
  2. Error may occur because of the use of 2 variable resistance.
  3. Observational error may also occur.


Also Read-Wheatstone bridge

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