To verify the laws of combination (series) of resistance using a meter bridge (R=R1 + R2 )

Aim : To verify the laws of combination (series) of resistance using a meter bridge (R=R₁ + R₂ )

Apparatus : a meter bridge , a leclanche cell (battery eliminator ) , a galvanometer , a resistance box , a jockey , two resistance wire or two resistance coils , set square , connecting wires .

Theory

1. The resistance (r) of a wire or coil is given by

Where R is the resistance from resistance box in the left gap and l is the length of the meter bridge wire from zero end upto balance point .

2. When two resistance r₁ & r₂ are connected in series , then their combined resistance

R₃=R₁+R₂

Procedure

1. Mark the two resistance coil as r₁ and r₂ .
2. To find the r₁ and r₂ proceed same way as in experiment 1.

(if r₁ and r₂ are not known )

1. Connect the two coils r₁ and r₂ in series as shown circuit diagram in the right gap of meter bridge and find the resistance of this combination. Take at least three sets of observation.
2. Record your observation.

Result

Within limits of experimental error , experimental and theoretical values of R  are same . Hence law of resistance in series is verified .

Precaution

1. The key should be inserted only while taking observation .
2. Connections should be neat and tight .

Sources of error

1. The key in resistance box may be loose .
2. The galvanometer may not show opposite deflection .

 

Circuit diagram

Observation table

Resistance in R.B. (ohm)	Balance l (cm)	(100-l) (cm)	[(100-l)*R]/l	Mean r1 (cm)
0.5	24	76	1.583	1.616
1	38	62	1.631
2	55	45	1.636

Resistance in R.B. (ohm)	Balance l (cm)	(100-l) (cm)	[(100-l)*R]/l	Mean r2 (cm)
0.5	33	67	1.015	1.015
1	50	50	1
2	66	34	1.030

Resistance in R.B. (ohm)	Balance l (cm)	(100-l) (cm)	[(100-l)*R]/l	Mean rs (cm)
0.5	16	84	2.625	2.615
1	28	72	2.571
2	43	57	2.651

Calculation

R₁ + R₂ = 1.616+1.015 = 2.631 ohm
R_s = 2.615 ohm

Therefore, experimental error = [(2.615-2.631)/2.615]*100 = 0.6%

Viva question

How does resistance change in series combination ?

Ans. Resistance increase in series combination

Why does resistance increase in series combination ?

Ans. Effective length of resistor increases . As R*l , resistance increases .

What is resistance ?

Ans. it is the opposition offered by the material of two wire to flow of electric current .

What is the cause of resistance ?

Ans. it is the opposition offered by the material of wire to flow of electric current .

What is the effect of temperature In the resistance of conductor ?

Resistance of all conductor increases with increase in temperature .

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