CBSE Science Practical File: 8-Part Guide

Your practical file earns marks before you ever touch a burette. In the 2026-27 CBSE scheme, Class 12 Physics, Chemistry and Biology each carry 30 practical marks out of 100, and the file is one slice of that. A neat CBSE science practical file with a sharp aim, a clean procedure and precautions that mean something also makes your viva easier. Here's how to write each part, with physics, chemistry and biology examples.

How many marks is a CBSE science practical file worth?

In the 2026-27 CBSE scheme, Class 12 Physics, Chemistry and Biology give 30% of the marks (30 out of 100) to practicals and 70% to a theory paper [1][5]. The practical file is one component, sitting beside the experiment you perform, the viva and the project. These are the numbers worth knowing:

 

A 5-mark record looks small until you remember it's one-sixth of your practical marks, and the same CBSE science practical file feeds your viva. The split for Chemistry and Biology differs, so check your subject's syllabus PDF on CBSE's academic website.

For Class 12, the board also appoints an external examiner at each school [3]. A stranger will flip through your file, so make it easy for them. And watch the calendar: the 2026 practical window ran from 1 January to 14/15 February [7]. If 2027 follows a similar pattern, aim to finish your file by December.

What are the 8 parts of a CBSE science practical file page?

Every experiment page has 8 parts, always in this order: aim, apparatus or materials, theory, procedure, observations, calculations, result and precautions. Most lab manuals for Class 12 follow this order, and your CBSE science practical file should too.

 

In many schools, a CBSE science practical file keeps diagrams on the blank left page and writing on the ruled right page. Ask your teacher once, then stick to it.

How do you write the aim in your CBSE science practical file?

Write the aim as one sentence that starts with "To" and a verb like find, determine, prepare or study. Copy the syllabus wording instead of inventing your own.

Physics practical file example

Aim: To find the resistance of a given wire using a metre bridge and hence determine the resistivity of its material.

It names the instrument and the final quantity, so the examiner knows what's coming before reading a line.

Chemistry practical format example

Aim: To determine the molarity of a KMnO4 solution by titrating it against a standard solution of oxalic acid.

Chemistry aims name both solutions and the thing you're finding. That's the whole job. Rusty on balanced equations for your theory section? Krutsha's Class 10 chemical reactions notes cover balancing [13].

Biology practical file example

Aim: To prepare a temporary mount to observe pollen germination.

Short wins here. Your labelled diagram does the heavy lifting later. And never tuck the result into the aim.

How do you write a procedure examiners can follow?

Number each step, put one action in each, and write them in the order you actually did them. Pick one tense and don't switch. Six to ten steps is a good range. Here's the KMnO4 titration, trimmed:

1.     Rinse the burette with KMnO4 solution, fill it, remove air bubbles from the nozzle and note the initial reading.

2.     Pipette the oxalic acid solution into a clean conical flask.

3.     Add dilute sulphuric acid and warm the mixture to about 60–70°C.

4.     Add KMnO4 from the burette drop by drop, swirling constantly.

5.     Stop at the first permanent light pink colour. KMnO4 is its own indicator, so you don't need another.

6.     Note the final reading and repeat until you get three concordant readings.

Physics procedures start with a labelled circuit or ray diagram. Biology procedures lean on the diagram you draw afterwards. In every subject, avoid "I did". Write the steps as instructions.

How do you write observations and calculations examiners can check?

Put every reading in a table with units in the column headings, then show one full sample calculation and list the rest in a results column. An examiner should be able to repeat your arithmetic in under a minute.

Write the least count of each instrument above the table, and take at least three readings. One reading can't show whether you were consistent.

Take the metre bridge. With a known resistance S and a balance length l, the unknown resistance is R = S × l / (100 − l). Say S is 10 Ω and the balance point is at 40 cm. Then R = 10 × 40 / 60 = 6.67 Ω. These numbers are only an illustration, so use your own readings. Resistivity then follows from ρ = Rπd²/4L, where d is the wire's diameter and L is its length.

End with the unit and a sensible number of digits. A final answer of 6.6666667 Ω shows you copied the calculator, not that you measured with a metre scale.

How do you write the result and sources of error?

State the result in one line with its value, unit and conditions, like "The resistance of the given wire is 6.7 Ω at room temperature." Then list the sources of error, which are the honest reasons your value might be slightly off.

• Physics: contact resistance at loose joints, end errors in the bridge wire, and the wire heating up.

• Chemistry: overshooting the end point by a drop, or reading the burette from the wrong eye level.

• Biology: a contaminated slide, or pollen that wasn't fresh.

Skip "human error". Name the specific thing that could have gone wrong, because that's what shows you understood the experiment.

How do you write precautions that earn marks?

Write precautions that are specific to the experiment and say why they matter. A line like "handle apparatus carefully" tells the examiner you didn't think about the experiment. Aim for four to six per experiment page of your CBSE science practical file.

 

Write every precaution as "do this, because that". It doubles as viva prep. "Why dilute sulphuric acid and not HCl?" is exactly the kind of question a viva can throw at you. For this titration, also read the upper meniscus, since the dark solution hides the lower one.

Which mistakes cost marks in a CBSE science practical file?

• Copying observations from a friend or a manual. Identical readings across files stand out fast, and the viva exposes the rest.

• Missing units, least count or range. A reading without a unit is half a reading.

• Messy diagrams. Draw in pencil, label with straight lines, and give every figure a caption.

• Gaps in the record. Physics expects at least 8 experiments and 6 activities [4], so a missing page is a risk.

• No teacher signatures or dates. Get them as you go, not the night before submission.

How do you prepare for the practical viva using your file?

Treat every line of your CBSE science practical file as a possible question. If you can't explain why a step or precaution is there, rewrite it until you can. Here are five to practise:

• Physics: Why is the balance point best near the middle of the wire? The percentage error in the result is smallest there.

• Physics: Why insert the key only while taking readings? Continuous current heats the wire and changes its resistance.

• Chemistry: Why warm the oxalic acid solution before titrating? The reaction is slow at the start in the cold.

• Chemistry: Why doesn't KMnO4 need an indicator? Its own pink colour marks the end point.

• Biology: Why add sucrose solution to the slide? It supplies nutrients and the right osmotic balance for the pollen tube to grow.

Say each answer aloud once. It takes a minute and sticks better than rereading.

How can Krutsha AI help with your CBSE science practical file?

Krutsha AI won't write your CBSE science practical file, and you wouldn't want it to, because a copied file collapses in the viva. It can help you understand what you're writing. The Formulas section gives each key formula with a summary of every variable, a worked example and the final unit, which is what your calculations section needs [9]. Our NCERT numerical solutions guide shows how to use step-by-step answers without just copying them [11]. Unsure why a precaution matters? Ask AskAI by typing the question or uploading a photo of your page, and see how the late-night doubt solver works [12]. Chapter notes for your syllabus sit in the Class 12 NCERT hub [14].

Frequently asked questions

What is the format of a CBSE science practical file?

Aim, apparatus, theory, procedure, observations, calculations, result and precautions, in that order. Physics adds sources of error; biology adds labelled diagrams.

How many experiments does the CBSE Class 12 Physics practical file need?

The 2026-27 Physics syllabus asks for at least 8 experiments and 6 activities, split equally between sections. Confirm in CBSE's official PDF.

How many marks is the science practical worth in CBSE Class 12?

Class 12 Physics, Chemistry and Biology carry 30 practical marks (30%) and 70 theory marks. A CBSE science practical file is one part of those 30.

How many precautions should I write for each experiment?

Four to six specific ones, each saying what to do and why. Physics files often add sources of error too.

Can I copy from a lab manual for Class 12 practical files?

Use it for aim and procedure wording, but write observations and results from your own readings. The viva tests that.

Ready to fix your CBSE science practical file tonight?

Pick the experiment page you like least. Rewrite the aim as one line, turn each precaution into a "do this, because that" sentence, and check your calculation against a formula you trust. Then move to the next page. If a step doesn't make sense, ask AskAI why. More guides are on the Krutsha AI blog [15].

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Sources and References