Question

experiment - verification of the ohm law using a simple electric circuit. ​

Answer 1

As performed in the real lab:

Material required :

A resistor of about 5 Ω, an ammeter ( 0 - 3 A), a voltmeter (0 - 10 V), four dry cells of 1.5 V each with a cell holder (or a battery eliminator), a plug key, connecting wires, and a piece of sand paper.

Precautions :

All the electrical connections must be neat and tight.

Voltmeter and Ammeter must be of proper range.

The key should be inserted only while taking readings.

Circuit Diagram:

Procedure :

Draw the circuit diagram as shown above.

Arrange the apparatus as per the circuit diagram.

Clean the ends of the connecting wires with sand paper and make them shiny.

Make the connections as per circuit diagram. All connections must be neat and tight. Take care to connect the ammeter and voltmeter with their correct polarity. (+ve to +ve and -ve to -ve).

Determine the zero error and least count of the ammeter and voltmeter and record them.

Adjust the rheostat to pass a low current.

Insert the key K and slide the rheostat contact to see whether the ammeter and voltmeter are showing deflections properly.

Adjust the rheostat to get a small deflection in ammeter and voltmeter.

Record the readings of the ammeter and voltmeter.

Take atleast six sets of readings by adjusting the rheostat gradually.

Plot a graph with V along x-axis and I along y-axis.

The graph will be a straight line which verifies Ohm's law.

Determine the slope of the V-I graph. The reciprocal of the slope gives resistance of the wire.

Observations:

Range of the given ammeter=.................... A.

Least count of the given ammeter = ..................... A.

Range of the given voltmeter = .....................V.

Least count of the given voltmeter = .....................V.

Mean value of V/I from observations, R = .......... Ω.

Observation from graph:

Slope of I vs V graph = ...........

R from graph = 1/ slope = .............. Ω.

Observation table:

As performed in the simulator:

Click on Show Label checkbox to label/unlable the apparatus in the circuit.

Click on Show Help checkbox to show/hide the 'help' for performing the lab.

Click on the Observation Table tab below to open the Observation table.

Drag the plug key to switch on/off the current.

Adjust the rheostat such that ammeter shows the low value of Current (I). Note corresponding voltmeter reading.

Increase the current by adjusting the slider of the rheostat and take about 5 or 6 sets of readings.

Note carefully ammeter and voltmeter readings in each set and record in the Observation Table.

Note V/I ratio for each set of reading in the Resistance column.

Click on Plot Graph button to plot voltmeter readings (V) along the x-axis and the corresponding ammeter readings (I) along the y-axis in the graph.

Answer 2

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Ohm's law states that the current through a conductor is proportional to the voltage V across its ends. It is written as V = l R, where R is the resistance of the conductor.

Ohm's law

Ohm's Law: The current I is proportional to the voltage V

Experiment to Verify Ohm's Law

Ohm's law can be easily verified in the lab or at home. You need a voltmeter, an ammeter, power supply (dry cells), resistors, and connecting wires. A simple procedure to verify Ohm's law is given below:

Ohm's law

A simple circuit to verify Ohm's law.

• Take four or five dry cells, a thin wire (AB), a voltmeter, an ammeter, a plug key and some thick connecting wires. Connect the circuit as shown in figure, using one cell. The plug key allows you to switch off the current when not required. The wire becomes quite hot when current passes through it for some time. This drains the cell as well. Therefore, insert the key into the plug to switch on the current only when taking measurements.

• The ammeter measures the current I through the circuit, and the voltmeter measures the potential difference V between the ends A and B of the wire. Note these values. Now, connect two cells in series in the circuit. You will find that the reading of the voltmeter increases, indicating the fact that a larger potential difference has been applied across the wire AB. You will also find that the reading of the ammeter increases as well. Note down the new values of V and I. Repeat the experiment by connecting in series three cells, four cells, and so on. In each case measure the potential difference and the current. If you calculate V/I for each case, you will find that it is almost the same. So, V/ l =R is a constant, which is another way of stating Ohm's law. Here, R is resistance of the wire AB. If you plot a graph of the current of the current I against the potential difference V, it will be a straight line. This shows that the current is proportional to the potential difference.

Ohm's law verification using Rheostat

A circuit with Rheostat to verify Ohm's law

The experimental setup used in the laboratory makes use of a Rheostat to vary the potential difference V across a standard resistor R.