Measurement of Resistance (Wheatstone's Bridge)

Practicle – 2
MEASUREMENT OF RESISTANCE ( WHEATSTONE’S BRIDGE)

AIM :-

You are given a Wheatstone bridge and other necessary instruments. Find the values of the unknown resistance Rx. Exchange the positions of unknown resistance and resistance box in the gaps of Wheatstone bridge and repeat the experiment.

PRINCIPLE :-

It works on the principle of balanced Wheatstone bridge.

APPARATUS:-    

Wheatstone-bridge (meter-bridge),

2 Volt Battery,

Rheostat,

Galvanometer,          

Jockey,

Key,

Resistance box(1 – 100  W),

Resistance coil.

Apparatus for Wheatstone's Bridge Practicle

 Precautions :-

1. Make proper and tight connections.
2. Keep the keys tightly closed in the resistance box.
3. Adjust the value of resistance box so that null point is obtained between 40 cm and 60 cm.
4. Do not slide the jokey continuously over the wire.

Note :-  Keep high resistance of rheostat in the beginning of each observation so that current is less and the galvanometer is not damaged. After getting approximate position of null point only decrease the resistance of rheostat.

(1) Condition :- Connect unknown resistance Rx between M – N.

Line Diagram For Wheatstone's Bridge

Wiring Diagram for Wheatstone’s Bridge.
Use this setup for carry out practical so it may be easy to understand.

Wiring Diagram for Wheatstone's Bridge

Measure L1 and L2 and note down in your Table.

(2) Condition :- Interchange unknown resistance Rx between P – Q.

In which interchange

Unknown  Resistance RX and Known Resistance Box RB.

Line  Diagram for Interchange RX And RB

Wiring Diagram for Wheatstone’s Bridge. (Condition-2)

In which interchange Unknown Resistance RX and Known Resistance Box RB.
Use this setup for carry out practical so it may be easy to understand.

Wiring Diagram for Interchange RX And RB

 

Conclusion :-

(1)   Unknown Resistance, Rx = …….. W

(2)    Unknown Resistance, Ry = ……...W

Law of Combinationof Resistors. (Wheatstone's Bridge),Video for std 8 to 12

Practical - 3

LAWS OF COMBINATION OF RESISTORS

( WHEATSTONE’S BRIDGE & POST OFFICE BOX )

AIM :-

You are given a Wheatstone Bridge and other necessary instruments. Find the values of the unknown resistance Rx and Ry . Now connect them in series and parallel respectively and measure their resultant resistances and test the laws of series and parallel connections.

PRINCIPLE :-     It works on the  principle of a balanced Wheatstone bridge. 

Apparatus :-   Wheatstone-bridge (meter-bridge),

                         2 Volt Battery,
                         Rheostat,
                        Galvanometer,
                        Jockey,
                        Key,
                        Resistance box(1 – 100 W),
                        Resistance coil.

Wheatstone Bridge Apparatus

(1)    Condition :- Connect unknown resistance R_x between  M – N.

Wheatstone Bridge line Diagram (Condition-1)

Wheatstone Bridge Wiring Diagram (Condition-1)

(2)    Condition :- Connect unknown resistance R_y between  M – N.

Wheatstone Bridge line Diagram (Condition-2)

Wheatstone Bridge Wiring Diagram (Condition-2)

(3)    Condition :- Connect unknown resistance in Series

Wheatstone Bridge line Diagram (Series connection)

Wheatstone Bridge Wiring  Diagram (Series connection)

(4)    Condition :- Connect unknown resistance in Parallel .

Wheatstone Bridge line Diagram (Parallel connection)

Wheatstone Bridge Wiring Diagram (Parallel connection)

                                                                                                                            

OBSERVATION TABLE

Wheatstone Bridge Observation table

CALCULATIONS :-

(1       (1) Series connection, R’s = Rx + Ry + …..W

(2)  Parallel connection, R’p = Rx Ry  /  Rx + Ry = ….W.

RESULT:-

(1) Unknown resistance, Rx = ….W, Ry = ….W

Wheatstone Bridge Observation table

 

CONCLUSION :

It is possible to verify the rules for series and parallel connections with the help of a meter bridge.

Precautions:-

(1) Make all connections tight.

(2)  Clean the ends of the connecting wire with a sand paper.

(3)  Plug keys of resistance box should be very tight.

(4)   Adjust the value of R from the resistance box such that null-point is obtained between 40 cm. and 60 cm.