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  • State Ohm’s law? How can it be verified experimentally? Does it hold good under all conditions? Comment.

State Ohm’s law? How can it be verified experimentally? Does it hold good under all conditions? Comment.

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Ohm’s law states that the electric current flowing through a conductor is directly proportional to the potential difference across the conductor as long as the temperature of wire doesn’t change and state of wire doesn’t change.
V \alpha I\\ V=IR\\ I=\frac{V}{R}

R is the proportionality constant called resistance at a given temperature.

Experimental setup for Ohm’s law verification:

 

1. Set up a circuit as shown in the figure. This is made up of a nichrome wire XY of length, say 0.5m, an ammeter, a voltmeter and four cells of 1.5 V each.

2. First use only one cell as the source in the circuit. Note the reading in the ammeter A, for the current and reading of the voltmeter V for the potential difference across the nichrome wire XY in the circuit. Note the readings.

3. Next, connect two cells in the circuit and note the respective readings of the ammeter and voltmeter for the values of current through the nichrome wire and potential difference across the nichrome wire.

4. Repeat the above steps using three cells and then four cells in the circuit separately.

5. Calculate the ratio of V to I for each pair of potential difference V and current I.

6. Plot a graph between V and I, and observe the nature of the graph

Once you plot the graph between V and I it will be a straight line with slope equivalent to resistance of wire. This is how we prove Ohm’s law experimentally. Make sure that the temperature in the room is same throughout the experiment.

Ohms law doesn’t obey all the time, it works only when temperature is constant.

 

 

 

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