# To study the dependence of current on the potential difference with graph

**Aim**

### To study the dependence of current (I) on the potential difference (V) across a resistor and determine its resistance. Also plot a graph between V and I.

**Materials Required**

- Battery eliminator
- Ammeter
- Voltmeter
- Rheostat
- One way plug key
- Resistor
- Connecting wires

**Theory**

#### Ohm’s Law:

At constant temperature, the potential difference (V) across a conductor is directly proportional to the current (I) flowing through it.

Mathematically,

V ∝ I

or V = IR

or R = V/I

Where, R is constant of proportionality and is known as resistance.

#### Factors affecting resistance:

- Length of the conductor (R ∝ l)
- Cross-section area of the conductor (R ∝ 1/A)
- Nature of the material

**Circuit Diagram**

**Procedure**

- Setup the devices as shown in the circuit diagram.
- Note the least count of the ammeter and the voltmeter.
- Plug the key on the battery eliminator and adjust the rheostat by sliding its variable terminal till the ammeter and the voltmeter show a reading.
- Note the readings of voltmeter and ammeter. Take out the plug or switch off the battery eliminator for a moment.
- Repeat the steps 3 and 4 for the different values of current by varying the sliding terminal of rheostat.
- Calculate resistance using formula
*R = V/I*. - Plot a graph by taking
*I*along y-axis and*V*along x-axis or vice-versa.

**Observation Table**

#### A. Least count and range of voltmeter and ammeter

Voltmeter | Ammeter | |

Range | 0 – 0.1 V | 0 – 0.5 A |

Least Count | 0.01 V | 0.01 A |

#### B. Readings of voltmeter and ammeter

S.No. | Potential difference (V) | Current (I) | Resistance R = V/I |

1. | 0.04 V | 0.02 A | R_{1} = 2 Ω |

2. | 0.06 V | 0.03 A | R_{2} = 2 Ω |

3. | 0.08 V | 0.04 A | R_{3} = 2 Ω |

**Calculation**

Mean value of R = = = 2 Ω

**Graph**

**Conclusions**

- For all the three readings, the R-value is the same and constant.
- The ratio of potential difference V and current I is the resistance of a resistor.
- With the help of the graph between V and I, Ohm’s law is verified as the plot is a straight line.

**Precautions**

- Thick copper wires should be used as connecting wires and using sandpaper, their insulation should be removed.
- The connections should be tight.
- Voltmeter should be connected in parallel with the resistor.
- To avoid unnecessary heating in the circuit, the current should be passed for a short time.

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