CLASS 10 / EXPERIMENT-1/ VERIFICATION OF OHM'S LAW

                                       CLASS 10 / EXPERIMENT - 1

VERIFICATION OF OHM'S LAW

Objective:

To verify the Ohm's law.

Statement of Ohm's Law:

Ohm’s law states that at a constant temperature, current 'I' through a conductor between two points is directly proportional to the potential difference or voltage 'V', across the two points.  

                                     

Thus, the ratio V : I is a constant. This constant is called as the resistance (R) of the conductor.

Graph:

After performing experiment for different readings of V & I and recording the observations, if we plot current on the x-axis of a graph and voltage on the y-axis of the graph, we will get a straight-line. The gradient of the straight-line graph is related to the resistance (R) of the conductor.

Related Theory:

Resistance:

• Resistance is the property of a component which restricts the flow of electric current. Energy is used up as the voltage across the component drives the current through it and this energy appears as heat in the component.
• Resistance is measured in ohms, the symbol for ohm is an omega(Ω).

Resistors connected in Series:

When resistors are connected in series their combined resistance is equal to sum of thier the individual resistances. For example if resistors R1 and R2 are connected in series their combined resistance, R, is given by:

Resistors connected in Parallel:

                              When resistors are connected in parallel their combined resistance is less than any of the individual resistances. Equation for the combined resistance R of 2 resistors R1 and R2 connected in parallel is given by:

                                             OR       

       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.

       Circuit diagram:

Procedure :

1. Draw the circuit diagram as shown above.
2. Arrange the apparatus as per the circuit diagram.
3. Clean the ends of the connecting wires with sand paper and make them shiny.
4. 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).
5. Determine the zero error and least count of the ammeter and voltmeter and record them.
6. Adjust the rheostat to pass a low current.
7. Insert the key K and slide the rheostat contact to see whether the ammeter and voltmeter are showing deflections properly.
8. Adjust the rheostat to get a small deflection in ammeter and voltmeter.
9. Record the readings of the ammeter and voltmeter.
10. Take atleast six sets of readings by adjusting the rheostat gradually.
11. Plot a graph with V along x-axis and I along y-axis.
12. The graph will be a straight line which verifies Ohm's law.
13. 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:

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.