In short: CBSE practicals carry 20-30 marks per subject — that is 60-90 marks across Science subjects alone. Most students score 22-27 out of 30 without much effort, but with proper preparation you can score 28-30. Practicals start in January 2027 at most schools. This guide covers exactly what happens in the practical exam, how to prepare for the viva, and common mistakes that cost marks.
How Much Do Practicals Matter?
| Class | Subject | Practical Marks | Theory Marks | Total |
|---|---|---|---|---|
| Class 10 | Science | 20 | 80 | 100 |
| Class 12 | Physics | 30 | 70 | 100 |
| Class 12 | Chemistry | 30 | 70 | 100 |
| Class 12 | Biology | 30 | 70 | 100 |
For Class 12 Science students, practicals are worth 90 marks total across PCM/PCB. A student who scores 28/30 in each practical has a 84-mark cushion before the theory exam even starts.
Class 10 Science Practical (20 Marks)
Breakdown
| Component | Marks |
|---|---|
| Practical file / record | 5 |
| Experiments | 8 |
| Activities | 2 |
| Project work | 3 |
| Viva | 2 |
| Total | 20 |
How to Prepare
Practical file (5 marks):
- Complete all experiments in your practical file before the exam
- Each experiment should have: Aim, Materials, Procedure, Observation Table, Result, Diagram
- Write neatly. Use a ruler for tables and diagrams.
- Get your teacher to sign each experiment as you complete it
Experiments (8 marks):
Common Class 10 Science experiments that appear in the practical exam:
- Determine the focal length of a concave mirror/convex lens
- Finding the pH of given solutions using pH paper/universal indicator
- Identifying acids and bases using indicators (litmus, phenolphthalein)
- Testing conductivity of solutions
- Study of soap and detergent cleaning capacity
- Preparing temporary slides of leaf/onion peel
- Observing homology and analogy in organisms
The external examiner picks 1-2 experiments for you to perform. Practice all of them at least once in your school lab before the exam.
Viva (2 marks):
- The examiner asks 2-3 questions about the experiment you just performed
- Questions are basic: "Why did you use this indicator?" "What would happen if you used a different solution?"
- Know the theory behind each experiment, not just the procedure
Class 12 Physics Practical (30 Marks)
Breakdown
| Component | Marks |
|---|---|
| Two experiments (8+8) | 16 |
| Practical record | 6 |
| Viva | 5 |
| Investigatory project | 3 |
| Total | 30 |
Important Experiments
- Determine resistance per cm of a given wire using metre bridge
- Verify Ohm's law using ammeter and voltmeter
- Find the focal length of a convex lens by plotting u-v graphs
- Determine the internal resistance of a cell using potentiometer
- Determine the refractive index of a glass slab
- Zener diode characteristics
- Transistor characteristics (common emitter)
How to score maximum:
- Draw circuit diagrams before starting the experiment
- Take at least 5-6 readings (not just the minimum 3)
- Plot graphs with proper axes, labels, scales, and units
- Show calculations clearly with proper significant figures
- If the result is unexpected, still write it honestly and mention possible sources of error
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Class 12 Chemistry Practical (30 Marks)
Breakdown
| Component | Marks |
|---|---|
| Volumetric analysis | 8 |
| Salt analysis (qualitative) | 8 |
| Content-based experiment | 4 |
| Project + Viva | 6 |
| Practical record | 4 |
| Total | 30 |
Key Preparation
Volumetric analysis (8 marks):
- Practice titration at least 5 times before the exam
- Concordant readings (within 0.1 mL) are essential
- Know the indicators: methyl orange (acid-base), phenolphthalein (acid-base), starch (iodometric)
- Write the balanced equation for the reaction
Salt analysis (8 marks):
- Memorize confirmatory tests for common cations: Fe²⁺, Fe³⁺, Cu²⁺, Zn²⁺, Al³⁺, Pb²⁺, Ca²⁺, Ba²⁺, NH₄⁺
- Memorize confirmatory tests for common anions: Cl⁻, SO₄²⁻, NO₃⁻, CO₃²⁻, CH₃COO⁻
- Practice the systematic procedure: preliminary tests → group analysis → confirmatory tests
Class 12 Biology Practical (30 Marks)
Breakdown
| Component | Marks |
|---|---|
| Major experiments (2) | 10 |
| Minor experiments (2) | 8 |
| Spotting (on slides/specimens) | 4 |
| Practical record + Viva | 5 |
| Investigatory project | 3 |
| Total | 30 |
Key Preparation
Common spotting items:
- Slides: T.S. of monocot/dicot root, stem, leaf; mitosis stages
- Specimens: Preserved flowers, seeds, insects
- Know scientific names and key features for each specimen
Major experiments:
- Prepare stained temporary mounts of onion peel/leaf peel
- Study pollen germination on a slide
- Identify features in prepared slides under microscope
Viva Preparation Guide (All Subjects)
The viva is where most students lose unnecessary marks. Typical questions are not difficult, but they require preparation.
Physics Viva Common Questions
- What is the principle behind this experiment?
- What are the sources of error?
- What would happen if you changed [variable]?
- Define the terms used in the experiment (resistance, focal length, etc.)
Chemistry Viva Common Questions
- What colour change indicates the end point?
- Why did you choose this particular indicator?
- What are the properties of the salt you identified?
- Write the balanced equation for the reaction.
Biology Viva Common Questions
- Identify the specimen and state its phylum/class.
- What is the function of [structure visible on slide]?
- How does [process] differ between monocot and dicot?
Preparation strategy:
- For each experiment, write 5 possible viva questions and their answers
- Know the theory chapter related to each experiment
- Practice answering aloud (not just in your head)
Common Mistakes That Cost Marks
- Incomplete practical file. If your file is missing experiments, you lose marks before the exam even starts. Complete it now.
- Not labelling diagrams. Circuit diagrams, apparatus setups, and biological drawings must be labelled.
- Fewer readings than required. Take 5-6 readings minimum, not the bare minimum 3.
- Not mentioning units. Every measurement must include units (cm, mL, Ω, etc.).
- Guessing in viva. If you do not know the answer, say "I am not sure" rather than giving a wrong answer. Examiners appreciate honesty over bluffing.
- Messy practical record. Use a ruler for tables. Write in pen (not pencil, except for diagrams). Keep it clean.
Timeline for Practical Preparation
| When | Action |
|---|---|
| November | Complete all experiments in your practical file. Get teacher signatures. |
| December | Practice 2-3 experiments per subject in the school lab. |
| January (before practical exam) | Revise all experiments. Write viva Q&A for each. Submit project files. |
| Practical exam day | Arrive early. Carry your practical file. Stay calm during viva. |
Frequently Asked Questions
When do CBSE practicals happen?
CBSE practical exams for Class 10 and 12 are conducted from January 1 onwards, typically before the theory exams in February-March. Each school schedules practicals independently within the CBSE-specified window.
Can I fail in practicals?
Technically yes — you need to pass both theory and practical components. But practical failures are extremely rare since the school conducts them. Most students score 70-90% in practicals.
Do practicals affect my overall percentage?
Yes. Practical marks are added to your theory marks for the final grade. A strong practical score (28-30 out of 30) significantly boosts your overall percentage, especially if your theory exam does not go perfectly.
Are the practical exams conducted by an external examiner?
For Class 12, yes — an external examiner from another school conducts the practical exam. For Class 10, the school's own teachers typically conduct the practical assessment.
What if I missed a practical class at school?
Talk to your teacher and arrange a makeup session. Your practical file must be complete before the exam. If you missed learning an experiment, practice it at home by watching the procedure and writing the observations.
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