eduphysics
CBSE AND NEET

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Resistance per cm of a given wire by plotting a graph between V and I

Apparatus Required

• Battery Eliminator 2 or 3 Amps
• One way plug key
• Rheostat 2.3 A, 56 Ohms
• Ammeter 0 to 3 A
• Resistance coil 100 cm or any desired length
• Voltmeter 0 to 3 V
• Resistance wire (alternative)
• Connecting wire (D.C.C)

Circuit Diagram- Resistance per cm of a wire

Experimental setup – Resistance per cm of a wire

Procedure

• Connect the ammeter in series with the circuit wire and the voltmeter in parallel with the wire.
• Note the zero error of the meters.
• Calculate the least count of the meters.
• Switch on the circuit.
• Set the rheostat to a particular position and record the readings of the ammeter and voltmeter.
• Repeat steps 5 and 6 for different settings of the rheostat.
• Tabulate the readings.
• Calculate the resistance of the wire using the formula R=V/I
• Resistance per cm is calculated from the above value.

Least count of ammeter

Least count of voltmeter

Resistance per cm of a wire-Tabular Column & Observation

Resistance of a wire – Graphical representation

Calculating the resistance by experimental and graphical method

Meter bridge- Resistance of a given wire and the resistivity of the material

METER BRIDGE – INTRODUCTION

INTRODUCTION

The physics experiment ‘Resistivity of the  material of the wire’ is an important experiment for class 12 students, particularly CBSE students.The resistivity values of various wires are used in everyday applications such as electrical wiring, heating elements, resistors, semiconductors, and material categorization, among others.This experiment exposes class 12 students to the resistivity values of various wires as well as the analysis of their results.

As part of this, the students measure the resistance of the wire, the screw gauge’s zero error, the radius of the wire, and the resistivity values using either Ohm’s law or the meter bridge method, using the proper formula.This practical ensures that the idea of resistivity is understood,its unit, as well as the values for various materials.Let us talk about this issue.

KNOWN RESISTANCE (RIGHT GAP) & UNKNOWN RESISTANCE (LEFT GAP)

EXPERIMENTAL METHOD- METER BRIDGE

KNOWN RESISTANCE (LEFT GAP) & UNKNOWN RESISTANCE (RIGHT GAP)

METER BRIDGE- EXPERIMENTAL METHOD

Meter bridge – Tabular column

Resistance of the given wire

PROCEDURE

• The meter bridge is an electrical device used to measure the resistance of an unknown resistor.
• It works on the principle of the Wheatstone bridge, which is a circuit with four resistors connected in a specific way. When the bridge is balanced, there is no current flow through the galvanometer.
• To use the meter bridge, first connect the resistors according to the circuit diagram.Then, select a known resistor from the resistance box and place it in the left hand arm of the bridge.
• Once the circuit connections are completed,the jockey is pressed near the end  A and then near end B of the meter bridge wire. If the deflections in the galvanometer are on one side , then there is some fault in the circuit connections.Check for double side deflections in the galvanometer.
• Move the jockey along the meter bridge wire until the galvanometer needle points to zero. 
• The point at which the jockey is located is called the balance point.
• The unknown resistance is calculated using the meter bridge resistance formula

METER BRIDGE – FORMULA

RADIUS OF THE WIRE USING SCREW GAUGE

ZERO ERROR IN SCREW GAUGE

NO ZERO ERROR

POSITIVE ERROR IN SCREW GAUGE

NEGATIVE ERROR IN SCREW GAUGE

PITCH OF THE SCREW GAUGE

LEAST COUNT OF A SCREW GAUGE

DIAMETER AND RADIUS OF THE WIRE

SCREW GAUGE – OBSERVATIONS

TABULAR COLUMN – RADIUS OF THE GIVEN WIRE, SCREW GAUGE

Resistivity of the material of the given wire

RESISTIVITY – IMAGE

RESISTANCE OF A WIRE

RESISTIVITY OF THE MATERIAL OF A WIRE

RESISTIVITY OF THE MATERIAL OF A WIRE – PROCEDURE

• The resistance of the given wire is to be calculated using the meter bridge.
• The principle of the meter bridge is  based on the Wheatstone bridge balancing condition.
• Using screw gauge, the radius of the given wire is to be determined.
• The given wire is stretched and  with the help of a meter scale, the length of the wire is to be measured.
• By applying these values we can calculate the resistivity of the given wire.

RESISTIVITY OF THE MATERIAL OF A WIRE – CALCULATION

RESISTIVITY OF THE MATERIAL OF A WIRE – RESULT

• The resistance of the given wire using using meter bridge(X) = 2.919 Ohms
• The resistivity of the material of the given wire = 6.739 X 10^-7 Ohm meter

CONCLUSION

The above-mentioned practical ‘Resistivity of the material of the wire’ is an important part of the class 12 physics practical curriculum.Students acquire hands-on experience measuring resistivity and learning how it changes for different materials, as well as the solution for material categorization and practical applications and also valuable knowledge for those pursuing careers in engineering or physics.

By participating in this sort of laboratory practical, students may hone their analytical and problem-solving abilities, which are crucial in the scientific area.Overall, it is a fun and educational approach to expose kids to the realm of physics and its practical applications.Did you ever spend the majority of your time in your physics lab?

Meter bridge -Verify the laws of combination of resistance

Series combination of resistance

Meter bridges – measuring R₁ and R₂

Meter bridge – Formula

Meter bridge – Series combination

Meter bridge – Tabular column for X₁

Meter bridge – Tabular column for X₂

S.No.	Known resistance   (R)	Balancing length  AJ=AD= (l)	Balancing length JC= DC=(100-l)	Unknown resistance X2=R(100-l)/l
	(in Ohms)	(in cm)	(In cm)	(in ohms)
1.	1.5	42	58	2.07
2.	1.4	41	59	2.01
3.	1.2	37	63	2.04
			Mean (X2 )

Meter bridge – Tabular column for series combination X=X₁+X₂

S.No.	Known resistance   (R)	Balancing length  AJ=AD= (l)	Balancing length JC= DC=(100-l)	Unknown resistance X2=R(100-l)/l
	(in Ohms)	(in cm)	(in cm)	(in Ohms)

Meter bridge -Verify the laws of combination of resistance

Parallel combination of resistance

Meter bridge-Tabular column for X₁

Observations & Calculations for Series Combination:

Meter bridge-Tabular column for X₂

S.No.	Known resistance   (R)	Balancing length  AJ=AD= (l)	Balancing length JC= DC=(100-l)	Unknown resistance X2=R(100-l)/l
	(in Ohms)	(in cm)	(in cm)	(in Ohms)
1.	1.5	42	58	2.07
2.	1.4	41	59	2.01
3.	1.2	37	63	2.04
			Mean X2	2.04

Meter bridge – Tabular column for parallel combination of resistors

S.No.	Known resistance   (R)	Balancing length  AJ=AD= (l)	Balancing length JC= DC=(100-l)	Unknown resistance X2=R(100-l)/l
	(in Ohms)	(in cm)	(in cm)	(in Ohms)
1.	1.2	50	50	1.2
2.	1.5	55.6	44.4	1.2

Potentiometer – Internal resistance of the given primary cell

INTRODUCTION

Potentiometers are a highly precise way of measuring the internal resistance of both primary (non-rechargeable) and secondary (rechargeable) cells.The experiment ‘potentiometer,internal resistance of a primary cell’ is a basic experiment that students may do using basic physics abilities.

It is precise and error-free since it draws no current from the cell.It is used to investigate the influence of ageing on cell performance as well as to troubleshoot issues with cell-powered products.This experiment validates the design of electrical circuits, the selection of appropriate power sources, and the optimization of battery performance.

POTENTIOMETER EXPERIMENT

CIRCUIT DIAGRAM

• AB –    Potentiometer
• Bt  –    Battery Eliminator (3 amps)
• K   –    One way plug key (in  the primary circuit) 
• K   –    One way plug key (in the secondary circuit)
• Rh-     Rheostat
• L   –    Leclanche cell
• HR-    High resistance
• G  –    Galvanometer
• R  –    Resistance box
• J   –    Pencil jockey positions   

POTENTIOMETER EXPERIMENT-SIMPLE CIRCUIT DIAGRAM

POTENTIOMETER EXPERIMENT-EXPERIMENTAL SET UP

POTENTIOMETER EXPERIMENT-FORMULA

PROCEDURE

• The circuit associations and the test set up are made as displayed previously.
• In the open circuit, when resistance is excluded (not included), the emf of the cell is determined by taking note of the balancing length.That is l1
• In the shut(closed) circuit, when the resistance is incorporated the balancing length is to be noted. That is l2
• The trial is rehashed for various values of R and the readings are organized.
• Utilizing the equation the internal resistance of the given cell can be determined.

TABULAR COLUMN & OBSERVATION

RESULT

The internal resistance of the given Leclanche cell is 7.16 Ohms

CONCLUSION

Physics practicals can be a valuable experience for students to learn concepts, develop important skills, develop problem-solving skills, develop experimental skills such as data collection, analysis, and interpretation, and develop communication skills, which can help them identify and correct errors in their work.

Practicals help students acquire the collaborative skills required for success in the sector.The experiment, internal resistance of a cell using a potentiometer, gives fundamental insights into cell activity and properties.This experiment’s simplicity makes it accessible to both students and academics.

POTENTIOMETER – COMPARISON OF EMF OF TWO CELLS

INTRODUCTION

Potentiometers are extremely precise equipment for detecting potential differences or emf.The experiment ‘potentiometer,comparison of emf of two cells’ is a basic experiment that students may do using their fundamental physics skills.Students may observe how emf is measured and how emf is related to the potential difference across a wire in this experiment.

This experiment aids in the comprehension of the idea of emf and how it relates to the electrochemical characteristics of cells.This experiment refers to tactical applications such as selecting the best battery for a certain device or evaluating the performance of various energy sources.

CIRCUIT DIAGRAM – POTENTIOMETER EXPERIMENT

DOUBLE POLE DOUBLE THROW SWITCH CONNECTIONS

POTENTIOMETER EXPERIMENT-POTENTIAL GRADIENT

For better results ,use freshly prepared cell otherwise, the polarisation effect will occur which is isolating barriers develop an interface between electrode and electrolyte.

The sensitivity of the potentiometer depends on a potential gradient (K).If the potential gradient is small  then the potentiometer is said to be more accurate and sensitive. 

EXPERIMENTAL SETUP-POTENTIOMETER EXPERIMENT

POTENTIOMETER EXPERIMENT – COMPARISON OF EMF OF TO CELLS-PROCEDURE

• This is the simplest circuit and all the connections are made as shown above. Connect the positive terminals of the auxiliary battery and primary cells to point A of the potentiometer (zero point).
• To check the correctness of the circuit, the pencil jockey is pressed near the end A and B of the potentiometer.
• If  the galvanometer shows two side deflections, then the circuit is correct, otherwise again check the circuit connections. 
• After confirming the double side deflections, the rheostat is adjusted at different positions.
• For each adjustment of the rheostat the corresponding balancing lengths (null deflection) for the two cells on the potentiometer wire are taken separately.
• The observed readings are to be entered in the tabular column

TABULAR COLUMN – POTENTIOMETER EXPERIMENT

POTENTIOMETER EXPERIMENT-CALCULATION & RESULT

OTENTIOMETER EXPERIMENT-EMF VERIFICATION

CONCLUSION

Physics practicals can be a valuable experience for students to learn concepts, develop important skills, develop their problem-solving skills, have the opportunity to develop their experimental skills such as data collection, analysis, and interpretation, and have the ability to develop their communication skills, which can help them identify and correct errors in their work.

Practicals assist pupils in developing collaborative skills, which are necessary for success in the industry. The potentiometer experiment measuring the emf of two cells is a good practical exercise in the study of electrical and electro-chemical concepts because of its accuracy, sensitivity, direct measurement, educational value, and real-world relevance.