Pr 3. De-Sauty Bridge

aTO MEASURE UNKNOWN CAPACITANCE USING DE-SAUTY BRIDGE APPARATUS REQUIRED1. de-sauty Bridge apparatus2. Connecting Wire3. AC power supplyTheory

Here,R2 - - Three decade resistance dials having value 10×1000Ω,10×100Ω and 10×10ΩR1… Single decade resistance dial having value 10×100Ω.C1… Unknown capacitor.C2…. Two fixed standard capacitors having value 0.01𝜇f & 0.1𝜇f (loss free)Terminals are provided for external connections to connect unknown capacitor and digital null detector . The De sautys bridge experiment is a direct carryover of the Wheatstone bridge with the DC source replaced by an AC source. The null detector we will be using also has an amplifier where the gain can be adjusted. This is connected to DMM which is used for getting the null point. The bridge is as follows. We can use the principle of a wheat stone bridge to calculate Cx as: C1=(R2/R1)×C2PROCEDURE -1 Connect unknown capacitor with the terminals marked unknown and digital null detector terminals with the terminals.2 Set the resistance dial R1 to some value say 1000 ohm and also set the standard capacitor C2 say at 0.1𝜇 fosition.3 Switch on the instrument.4 Now adjust the decade resistance dial R2 to minimize the readings in the digital null detector. (minimum readings may be 0.00-0.08 )5 Note the value R1,R2 and C2 and calculate the value of unknown capacitor using above formula.5 Repeat the above experiment on different value of resistance R1&C2. OBSERVATION

SN	CapacitanceC2 (𝜇F)	ResistanceR1 (Ohm)	ResistanceR2 (Ohm)	C1=R2 R1⨯ C2	Mean C1(𝜇F)
1	0.01	100
2	0.01	200
3	0.1	100
4	0.1	200
5	0.1	300
6	0.1	400
7	0.1	500
8	0.1	600
9	0.1	700
10	0.1	800
11	0.1	900
12	0.1	1000

Result:Capacitance of unknown capacitor is found to be .............Precaution:1. Reistance of R1and R2 should be increased gradually.2. Connecting wire should not be loose.3. Reading in null delfection meter should be taken after a while of changing the reistance.4. Source of ac should be uniform (Non flucuating).