AIM To determine the resistance per cm of a given wire by plotting a graph of potential difference versus current.
Battery, key, rheostat, voltmeter, ammeter, resistance wire (unknown resistance), connecting wires, meter scale, sandpaper.
This Experiment is based on OHM’S LAW
Ohm’s Law states that the electric current passing through a conductor is directly proportional to the potential difference applied across its ends.
The resistance R of the wire depends on the material of the wire and its dimensions.
- Draw the circuit diagram as shown in figure above
- Arrange the apparatus as per the circuit diagram
- Clean the ends of the connecting wires with sandpaper 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 at least six sets of readings by adjusting the rheostat gradually
- Plot a graph with V along X axis and I along 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 the resistance of the wire.
Range of the given Ammeter = 0-500m A
Range of the given voltmeter = 0-5V
- Least Count
Least Count of the given Ammeter = 10mA
Least Count of the given voltmeter = 0.1V
- Zero Error
Zero Error of the given Ammeter = 0A
Zero Error of the given voltmeter = 0V
- Zero Correction
Zero Correction of the given Ammeter = 0A
Zero Correction of the given voltmeter = 0V
- Observation Table for Ammeter and Voltmeter Readings
|S No||Ammeter Observed (A)||Ammeter Corrected (A)||Voltmeter Observed (V)||Voltmeter Corrected (V)||Ratio (V/I) = R (ohm)|
Mean Value of V/I from observations, R = 0.28Ω
Length of resistance wire = 40.2cm
Value of slope of VI graph =0.27 Ω
Resistance per unit length = 0.675 Ωm-1
- Ohm’s Law is verified as the I vs V graph is a straight line
- The resistance of the given wire = 0.28Ω
- The resistance per cm of given wire is 0.675 Ω m-1.
- All the electrical connections must be neat and tight.
- Voltmeter and Ammeter must of proper range
- The key should be inserted only while taking readings.
- Give the mathematical form of Ohm’s law.
V = RI, is the mathematical representation of Ohm’s law.
- State Ohm’s Law
Ohm’s law states that the electric current ‘I’ flowing through a conductor is directly proportional to the potential difference V (voltage) across its ends (provided that the physical conditions, temperature, pressure, and dimensions of the conductor remain same).
- What is the material chosen for rheostat wire and why?
It is constantan alloy. It is chosen to make rheostat as its resistivity is very high and temperature coefficient of resistance is quite small.
- What is the material used for making connection wires?
Here, copper has been used.
- What are the factors affecting resistance?
The resistance depends upon length, the area of cross-section, nature of material and temperature of conductors.
- What is electrical current? Define its S.I. unit?
The flow of electric charge per unit time through a conductor is called the electric current. It’s S.I. unit is ampere (A). 1 Ampere is the amount of current flowing in a conductor which offers resistance 1 Ohm when 1 V potential difference is maintained across the conductor.
- Define S.I. Unit of electric potential.
S.I. unit of electric potential is Volt. 1 Volt is said to be the potential difference between two points if 1 joule of work is done in bringing 1 coulomb of charge from one point to the other.
- Why is ammeter connected in series?
To measure the current without any change in magnitude.
- Why is voltmeter connected in parallel?
A voltmeter is connected in parallel so that it can measure the potential drop without any change in its magnitude.