Determination of the equivalent resistance of two resistors are connected in series combination

 SERIES COMBINATION OF RESISTORS

When two or more resistors are joined/connected end to end it is known as a Series combination & the same current flows through each one of them but the voltage (potential difference) varies across the resistors. In this experiment, the current is made to flow between resistors connected in a series combination. 

Aim of the experiment :

To determine the equivalent resistance of the two resistors when connected in a series combination. OR To verify the law of combination of resistances in series combination.

Apparatus required :

1. Meter bridge
2. Two resistors of different values
3. Galvanometer
4. Plug Key
5. Battery
6. Jockey
7. Connecting wires

Principle of the experiment :

01. Wheatstone's bridge is balanced when the current through the galvanometer is zero.

02. If P, Q, R & S represent the resistances of four arms of Wheatstone's bridge. Then , P/Q = R/S

Formula :

01. Resistance, Rs = Sl/(100-l)

Where,

            S - Standard resistance

            l - The balancing length

02. Equivalent resistance in series, Rs = R1+R2

Where,

            R1 & R2 - Individual resistances of different values 

Circuit diagram :

The equivalent resistance of two resistors is connected in series

Procedure :

• The connections are made as shown in the circuit diagram respectively.

• A suitable standard resistance S is unplugged into the resistance box.

• The circuit is checked for opposite deflections by placing the Jockey at the two ends of the meter bridge wire AC alternately.

• The jockey is moved on the wire from end A towards C till the Galvanometer shows zero deflection.

• The balancing length, l is measured. The equivalent resistance of the series combination is calculated using the formula. Rs = Sl/(100-l)

• The experiment is repeated for the different S values and the average Rs value is calculated.

Observation :

01. Resistance, R1 = ................................Ω 

02. Resistance, R2 = ................................Ω 

Tabular column :

Trial No	Resistance, S in (Ω Ohm)	Balencing length, l in (cm)	(100 - l) in (cm)	Resistance, Rs = Sl/(100 - l) in (Ω Ohm)
01.
02.
03.
04.
05.
				Mean Rs = ...........Ω

Calculations :

01. Theoretical value of equivalent resistance, Rs = R1 + R2 = ................................Ω 

Result : 

The theoretical value of resistance Rs = ...............Ω is nearly equal to the experimental value of resistance Rs = ...............Ω . Hence the law of combination of resistances in series is verified.