Name: Ohm’s Law & Introduction to Electric Resistance
Uploaded: 2019-07-19
Duration: 8 min 43 s
Description: In our attempt to establish a relationship between current and voltage, we will discover a new physical quantity in this video. Let's watch and learn.

Question

Describe an activity to verify Ohm&rsquo;s law experimentally. Also, state Ohm's law and write the precautions that you should take while performing this Activity.

Accepted Answer

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

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.

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.

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

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

In this Activity, you will find that approximately the same value for $\frac{V}{I}$ is obtained in each case. Thus, the $V - I$ graph is a straight line that passes through the origin of the graph, as shown in figure below. Thus, $\frac{V}{I}$ is a constant ratio.

The potential difference, $V$ , across the ends of a given metallic wire in an electric circuit is directly proportional to the current flowing through it, provided its temperature remains the same. This is called Ohm’s law.

$\Rightarrow V α I$

or $\frac{V}{I} = constant$

or $V = I R$

R is a constant for the given metallic wire at a given temperature and is called its resistance. It is the property of a conductor to resist the flow of charges through it.

Precaution must be taken during the activity that the current does not flow through the resistor continuously. This leads to heating of the resistance wire and its resistance changes. As a result, Ohm’s Law is not correctly verified.

Describe an activity to verify Ohm’s law experimentally. Also, state Ohm's law and write the precautions that you should take while performing this Activity.

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