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Home Physics Class 12 Physics To verify the laws of combination (series & parallel) of resistances using meter bridge (slide Wire Bridge)
Class 12 Physics Lab Experiments

To verify the laws of combination (series & parallel) of resistances using meter bridge (slide Wire Bridge)



Aim

To verify the laws of combination (series & parallel) of resistances using meter bridge (slide Wire Bridge)

Apparatus

A meter bridge, laclanche cell, a galvanometer, a resistance box, a jockey, two resistances wires, set square, sand paper and connecting wires.

Series and Parallel Combination of Resistances

Observations: Table for length (ι) & unknown resistance (r):

Resistant Coil Obs. No. Resistance from resistance box,R (ohm) Length BC = (100-ι) cm Resistance r = 100-ι/ι.R Mean Resistant (ohm)
r1only 1/2/3 0.5/1.0/1.5 35/43/50 65/57/50 0.92/1.32/1.5 1.24
r2only 1/2/3 0.5/1.0/1.5 30/38/46 70/62/54 0.16/1.63/1.76 1.51
r2 & r 2 in series 1/2/3 1.3/2.2/3.5 34/45/54 66/55/46 2.52/2.68/2.97 1.72
r2 & r 2 in parllel 1/2/3 2/3/4 75/82/86 25/18/14 0.67/0.66/0.65 0.66

Calculations:

  1. In Series: Experimental value of R S= 2.72Ω

  2. Theoretical value of RS=r1+ r 2= 2.75Ω

  3. In Series: Experimental value of R S= 2.72Ω

  4. In parallel: Experimental value of R P=0.66Ω

  5. Theoretical value of RP=r1r2 /r1+ r2= 0.68Ω

Result:Within limits of experimental error, experimental & theoretical values of R Sare same. Hence the law of resistance in series i.e. R s= r 1+ r 2 is verified. (1) Within limits of experimental error, experimental & theoretical values of R p are same. Hence law of resistances in parallel i.e. Rs= r1r2/r1+r2 is verified.

Precautions:

  1. The connections should be neat, clean & tight.
  2. Move the jockey gently over the wire & don’t rub it.
  3. All plugs in resistant box should be tight.

Sources of Error:

  1. The plugs may not be clean.
  2. The instrument screws maybe loose.