Class 12 Physics Lab Manual – Galvanometer, Ammeter and Voltmeter

The experiment on Galvanometer, Ammeter and Voltmeter is one of the most important and conceptual practical activities in the Class 12 Physics syllabus. This experiment focuses on understanding the working principle of a moving coil galvanometer and learning how to convert it into an ammeter and a voltmeter. The practical examination conducted under the supervision of the Central Board of Secondary Education evaluates students on their ability to set up circuits correctly, apply formulas accurately, record observations properly, and explain theoretical concepts during viva voce.

This experiment strengthens the fundamental understanding of current electricity and measuring instruments. It also helps students develop analytical skills and practical confidence required for both board exams and competitive examinations.

Studentbro.in provides a detailed and structured guide to help Class 12 students prepare effectively for the Galvanometer, Ammeter and Voltmeter practical experiment.

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Direct Links to Download CBSE Lab Manual STD 12th English Medium (PDF)

► Click “Download Here” next to your subject to access the free PDF. 

1	General Introduction	Download Here
2	Current Electricity – Sources & Accessories	Download Here
3	Measurement of Resistance	Download Here
4	Measurement of Electromotive Force and Potential Difference	Download Here
5	Galvanometer Ammeter and Voltmeter	Download Here
6	Frequency of A C (Alternating Current) Mains	Download Here
7	Focal Length of Spherical Mirrors	Download Here
8	Focal Length of Spherical Lenses	Download Here
9	Refractive Index of Prism Material Glass Slab and Transparent Liquid	Download Here
10	Semiconductor Diodes and Transistors	Download Here
11	Activities	Download Here
12	Experiment	Download Here

Understanding a Galvanometer

A galvanometer is a sensitive electrical instrument used to detect and measure small electric currents. It works on the principle that a current-carrying conductor placed in a magnetic field experiences a force.

In a moving coil galvanometer:

• A coil is placed between the poles of a strong magnet.

• When current passes through the coil, it experiences a torque.

• The coil rotates, causing deflection of the pointer.

The deflection is directly proportional to the current flowing through the coil, provided the magnetic field is uniform.

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Need for Converting Galvanometer

A galvanometer can measure only small currents. To measure large currents or high potential differences, it must be converted into:

• An Ammeter (to measure current)

• A Voltmeter (to measure potential difference)

This conversion is achieved by connecting appropriate resistances in series or parallel with the galvanometer.

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Objectives of the Experiment

The main objectives of the Galvanometer experiment are:

• To determine the resistance of a given galvanometer

• To convert a galvanometer into an ammeter

• To convert a galvanometer into a voltmeter

• To verify the conversion practically

• To understand the working of electrical measuring instruments

This experiment provides both conceptual clarity and practical skill development.

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Apparatus Required

The commonly used apparatus include:

• Moving Coil Galvanometer

• Resistance Box

• Known Resistances

• Rheostat

• Battery or Cell

• Plug Key

• Connecting Wires

• Ammeter and Voltmeter (for comparison)

Students must ensure proper functioning of all instruments before performing the experiment.

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Conversion of Galvanometer into Ammeter

To convert a galvanometer into an ammeter, a low resistance called shunt is connected in parallel with the galvanometer.

The shunt allows most of the current to pass through it, protecting the galvanometer from damage due to high current.

Formula used:

S = (Ig × G) / (I − Ig)

Where:
S = Shunt resistance
Ig = Full-scale deflection current of galvanometer
G = Resistance of galvanometer
I = Desired current range

After connecting the shunt, the galvanometer can measure higher currents and function as an ammeter.

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Conversion of Galvanometer into Voltmeter

To convert a galvanometer into a voltmeter, a high resistance called series resistance is connected in series with the galvanometer.

The series resistance limits the current passing through the galvanometer and allows it to measure higher potential differences.

Formula used:

R = (V / Ig) − G

Where:
R = Series resistance
V = Desired voltage range
Ig = Full-scale deflection current
G = Resistance of galvanometer

This conversion enables the instrument to function as a voltmeter.

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Circuit Diagram and Its Importance

Drawing accurate circuit diagrams is essential for scoring well in practical exams. Students must:

• Use standard electrical symbols

• Show shunt in parallel for ammeter

• Show series resistance for voltmeter

• Indicate correct polarity

• Label all components clearly

A neat and correct diagram reflects strong conceptual understanding.

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Procedure for the Experiment

The general procedure includes:

1. Set up the circuit to determine galvanometer resistance.

2. Measure full-scale deflection current.

3. Calculate required shunt resistance.

4. Connect shunt in parallel to convert into ammeter.

5. Verify readings with standard ammeter.

6. Calculate series resistance for voltmeter conversion.

7. Connect resistance in series.

8. Verify readings with standard voltmeter.

All readings must be recorded carefully in tabular form.

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Observation Table Format

Observation tables generally include:

• Applied current or voltage

• Galvanometer deflection

• Calculated resistance values

• Comparison readings

Proper units (Ampere, Volt, Ohm) must be mentioned clearly.

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Calculations and Result

Students must:

• Apply formulas correctly

• Show step-by-step calculations

• Calculate shunt and series resistance accurately

• Compare experimental values with standard values

• Write final result with proper units

Correct calculations are crucial for scoring maximum marks.

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Precautions to Be Taken

While performing this experiment, students should follow these precautions:

• Ensure tight and clean connections

• Avoid excessive current

• Check zero error before starting

• Do not exceed galvanometer limits

• Close key only while taking readings

• Avoid parallax error

Following precautions ensures safety and accurate results.

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Sources of Error

Possible sources of error include:

• Loose connections

• Incorrect resistance value

• Heating effect

• Instrumental error

• Wrong formula application

Students should analyze these errors in their practical record.

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Viva Questions on Galvanometer, Ammeter and Voltmeter

Common viva questions include:

• What is a galvanometer?

• State the principle of moving coil galvanometer.

• Why is shunt used in ammeter?

• Why is high resistance connected in voltmeter?

• Define full-scale deflection current.

• What is the SI unit of current and voltage?

Conceptual clarity helps students answer confidently.

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Marking Scheme for the Practical

The experiment is evaluated based on:

• Proper circuit setup

• Observation accuracy

• Correct calculations

• Neat practical record

• Viva performance

Maintaining a complete and certified practical file is essential.

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Applications in Daily Life

Understanding galvanometer conversion helps students understand:

• Functioning of electrical meters

• Household energy meters

• Electronic measuring devices

• Circuit design and testing

• Electrical engineering principles

These concepts are fundamental in electrical and electronics industries.

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Common Mistakes to Avoid

Students should avoid:

• Connecting shunt incorrectly

• Using wrong resistance values

• Drawing untidy diagrams

• Ignoring units

• Skipping calculation steps

Avoiding these errors improves overall performance.

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Tips to Score High in This Practical

To secure maximum marks, students should:

1. Understand principle clearly.

2. Practice circuit connections repeatedly.

3. Memorize important formulas.

4. Maintain neat practical file.

5. Prepare viva questions thoroughly.

6. Stay calm and confident during examination.

Confidence and clarity ensure excellent results.

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Importance for Competitive Exams

The concepts of galvanometer conversion are frequently asked in engineering entrance examinations and other competitive tests. A strong understanding of measuring instruments enhances problem-solving speed and conceptual strength in current electricity.

Students planning careers in electrical engineering, electronics, or applied sciences benefit greatly from mastering this experiment.

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How Studentbro.in Supports Class 12 Students

Studentbro.in provides:

• Step-by-step experiment explanation

• Circuit diagram guidance

• Formula and calculation support

• Viva question bank

• Practical preparation tips

• Updated syllabus information

Our mission is to provide reliable, structured, and exam-focused academic content to help students excel in board examinations.

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Conclusion

The Class 12 Physics Lab Manual – Galvanometer, Ammeter and Voltmeter experiment is essential for understanding electrical measuring instruments and their practical applications. It teaches students how to convert instruments safely, apply formulas correctly, and analyze experimental results accurately.

By following the official guidelines of the Central Board of Secondary Education and practicing regularly in the laboratory, students can confidently perform this experiment and secure excellent marks in their Physics practical examination.

Studentbro.in remains committed to supporting Class 12 students with comprehensive, easy-to-understand, and exam-oriented educational resources for academic success.