**Aim** : To verify the laws of combination (series) of resistance using a meter bridge (R=R_{1} + R_{2} )

**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 **

- 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 r_{1} & r_{2} are connected in series , then their combined resistance

R_{3}=R_{1}+R_{2}

**Procedure **

- Mark the two resistance coil as r
_{1}and r_{2}. - To find the r
_{1}and r_{2}proceed same way as in experiment 1.

(if r_{1} and r_{2} are not known )

- Connect the two coils r
_{1}and r_{2}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. - 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 **

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

**Sources of error **

- The key in resistance box may be loose .
- 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 r_{1} (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 r_{2} (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 r_{s} (cm) |

0.5 | 16 | 84 | 2.625 | 2.615 |

1 | 28 | 72 | 2.571 | |

2 | 43 | 57 | 2.651 |

**Calculation **

R_{1} + R_{2} = 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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