Important Questions Physics Class 12 2025-26 PDF with Solution

Physics is the language of nature. It’s not just formulas and numericals, but the logic behind how the world works. Every law, every derivation has a meaning , and when you understand that meaning, the marks naturally follow.

This guide is written to make your revision simple and smart. We’ll go chapter by chapter, understand what’s important, why it matters, look at the most expected questions, learn how to write answers that fetch full marks, and end each chapter with short FAQs and friendly advice.

Take this as your final prep before exams, clear, honest, and designed to keep you focused. Below, we have provided the links to downloadable PDFs of chapter-wise important questions for class 12 Physics and that too for different categories of marks.

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Important Question Answers of Class 12 Physics

Q1. State Gauss’s Law and derive the electric field due to an infinitely long straight charged wire.

Ans. Gauss’s Law states that the total electric flux through a closed surface is equal to the charge enclosed divided by epsilon zero. To find the electric field, imagine a very long straight wire carrying charge uniformly. Take a cylindrical surface around it so that the field is the same everywhere on the curved surface. Only the curved surface contributes to flux because the electric field is perpendicular to it but parallel to the flat ends.
Flux = Electric field × curved surface area = E × (2 pi r L).
Charge enclosed = lambda × L.
Using Gauss’s Law: E × 2 pi r L = lambda L / epsilon zero.
Cancel L to get: E = lambda / (2 pi epsilon zero r).
Thus, the electric field decreases as the distance from the wire increases.

Q2. Derive the expression for energy stored in a capacitor.

Ans. When a capacitor is charged, small work has to be done to move small charge dq against the increasing potential difference.
At any instant, V = q/C.
Small work done dW = V dq = (q/C) dq.
Integrate from q = 0 to q = Q:
Work done W = Q squared divided by (2C).
Since Q = C V, substitute to get W = 1/2 C V squared.
This stored energy is held in the electric field between the plates of the capacitor.

Q3. A wire of resistance 20 ohm is stretched to double its length. Find its new resistance.

Ans. When a wire is stretched, length becomes double and area becomes half because volume stays constant. Resistance is proportional to length divided by area.
New resistance = (2L) divided by (A/2) = 4 times original.
So R new = 4 × 20 = 80 ohm.
This shows that stretching a wire increases resistance significantly.

Q4. State the principle of a moving coil galvanometer.

Ans. A moving coil galvanometer works on the principle that a current carrying coil placed in a magnetic field experiences a torque. When current flows through the coil, the magnetic field interacts with it and produces a turning effect. 

The deflection of the pointer is directly proportional to the current. This makes the instrument useful for measuring very small currents accurately.

Q5. Distinguish between diamagnetic, paramagnetic and ferromagnetic materials.

Ans. Diamagnetic materials: very weakly repelled by magnets. They have no permanent magnetic moment. Examples: copper, bismuth. Paramagnetic materials: weakly attracted by magnets. They have small permanent magnetic dipoles which align in the presence of a field. Examples: aluminium, sodium. Ferromagnetic materials: strongly attracted and can be permanently magnetised because their atomic dipoles align strongly. Examples: iron, cobalt, nickel.

Q6. State Faraday’s law of electromagnetic induction.

Ans. Faraday’s law states that the induced emf in a closed loop is equal to the negative rate of change of magnetic flux through the loop. This means whenever the magnetic field around a conductor changes, current is induced in it. It explains how generators, transformers and induction coils work.

Q7. What is the power factor? Why is it important in AC circuits?

Ans. Power factor is the cosine of the phase difference between voltage and current.
It tells how efficiently electrical energy is being used. A high power factor means less wastage of power and better performance of appliances. Industries try to keep power factor close to 1 to avoid extra charges and reduce losses.

Q8. What are electromagnetic waves? Mention two characteristics.

Ans.  Electromagnetic waves are waves formed by oscillating electric and magnetic fields. They do not need any medium and can travel through vacuum. Two characteristics:

Q9. What is total internal reflection? Give one example.

‍Ans. Total internal reflection occurs when light travels from a denser medium to a rarer medium and strikes the boundary at an angle greater than the critical angle. In this case, light is completely reflected back inside the denser medium. Example: Working of optical fibres used in internet cables.

Q10. Define interference of light.

Ans.  Interference of light occurs when two coherent light waves superpose to produce bright and dark fringes on a screen. Bright fringes occur due to constructive interference while dark fringes occur due to destructive interference. Young’s double slit experiment is a classic demonstration.

Q11. State Einstein’s photoelectric equation.

Ans. Einstein explained that light consists of packets of energy called photons.
Energy of photon = h nu.
This energy is used first to release the electron from metal (work function) and the remaining becomes kinetic energy.
So: h nu = work function + kinetic energy.
This explains why frequency, not intensity, controls photoelectric emission.

Q12. State Bohr’s two main postulates for hydrogen atoms.

Ans. Postulate 1: Electrons revolve around the nucleus only in certain fixed orbits where they do not radiate energy. Postulate 2: Electrons emit or absorb energy only when they jump between these orbits. The energy difference appears as radiation of definite frequency.

Q13. What is a mass defect? What is binding energy?

Ans. Mass defect is the difference between the actual mass of a nucleus and the total mass of its individual protons and neutrons. Binding energy is the energy that must be supplied to break the nucleus into separate nucleons. It is also the energy released when the nucleus is formed.A higher binding energy means a more stable nucleus.

Q14. What is a p-n junction diode? Explain its behaviour in forward bias.

‍Ans. A p-n junction diode is formed by joining p-type and n-type semiconductors. In forward bias, the positive terminal of the battery is connected to the p-side and negative to the n-side. This reduces the barrier potential and allows current to flow easily. Thus, the diode conducts in forward bias.

Q15. What is modulation? Why is it necessary?

Ans. Modulation means combining a low frequency message signal with a high frequency carrier signal.It is necessary because low frequency signals cannot travel long distances.High frequency carrier waves carry the information efficiently through antennas.

Q16. What is electric flux?

Ans. Electric flux is a measure of how many electric field lines pass through a given surface. A strong electric field produces higher flux. It helps in understanding Gauss’s law and distribution of electric fields.

Q17. State Ohm’s Law and mention its limitations.

Ans. Ohm’s Law states that the current flowing through a conductor is directly proportional to the potential difference across its ends, provided the temperature and physical conditions of the conductor remain constant.

That is, V ∝ I or V = IR

where:

• V = Potential difference across the conductor
• I = Current flowing through the conductor
• R = Resistance of the conductor

Limitations of Ohm’s Law:

1. It is not applicable to non-ohmic materials like semiconductors, diodes, or transistors.
2. It fails when temperature changes, as resistance of materials varies with temperature.
3. It does not hold true for electrolytes or vacuum tubes, where current and voltage are not directly proportional.
4. It applies only when the physical state (length, area, etc.) of the conductor remains unchanged.

Q18. What is self-induction?

Ans. Self-induction occurs when a changing current in a coil changes the magnetic field around it, which then induces an emf in the same coil. This induced emf opposes the change in current. It is used in choke coils and inductors.

Q19. State mirror formula for spherical mirrors and explain its meaning.

Ans. Mirror formula is: 1 over focal length = 1 over image distance + 1 over object distance. It relates the position of object, image and focal length for a concave or convex mirror. Using this, you can calculate where the image will form if the object distance is known.

Q20. What is resonance in an LCR circuit?

Ans. Resonance occurs when the inductive reactance equals the capacitive reactance in an AC circuit. At this point, the impedance becomes minimum and current becomes maximum. Resonance is used in tuning radios and filtering circuits.

EXTRA QUESTIONS FOR PRACTICE 

Q1. What is the principle of a potentiometer? How can it be used to compare the EMF of two cells?

Q2. State the conditions for resonance in an LCR series circuit and write its significance.

Q3. Explain how eddy currents are produced and mention two applications of eddy currents.

Q4. Define magnetic susceptibility and relative permeability. Write about their relationship.

Q5. Explain the working of a step-up transformer with a neat labeled diagram.

Q6. Derive the mirror formula for a concave mirror and state the assumptions made.

Q7. State the principle of a transistor as an amplifier and draw its circuit diagram.

Q8.What is polarization of light? How can it be produced?

Q9. Describe the experimental setup and principle of Young’s Double Slit Experiment.

Tips to Use These Class 12 Physics Important Questions the Right Way

Before you start solving, here’s how to make your Class 12 Physics important questions practice actually help (and not just feel like another homework session):

• Revise NCERT theory first, then move to the important questions - it helps you link concepts with real exam problems.
• For numerical questions, always write the formula first, then substitute values, and finally solve - CBSE gives marks for each step.
• Don’t skip theory-based questions - many students focus only on numericals, but definitions, laws, and principles are equally scoring.
• Use a timer while solving a full set - it trains you to manage 3-mark and 5-mark questions within time.
• Maintain a formula and units sheet for every chapter and glance through it daily before practice.
• And when you get something wrong, try it again later without checking the solution — that’s how you actually fix weak areas.

Benefits of Practising These Class 12 Physics Important Questions

Here’s why these Class 12 Physics important questions are a total must for smart prep:

• You’ll get used to the exact CBSE question style - conceptual, numerical, and derivation-based.
• These questions focus on the most scoring parts of each chapter, so your revision becomes sharper and faster.
• You’ll learn to present your answers neatly, showing formulas, steps, and diagrams just how CBSE expects.
• Regular practice strengthens key concepts in chapters like Electrostatics, Current Electricity, Optics, Dual Nature, and Semiconductors.
• It boosts time management, since you’ll know exactly how long each question type takes.
• Repetition helps spot your weak areas early - so you can fix them before the exam rush.
• And the best part? Numerical practice builds accuracy and cuts down silly calculation mistakes - a total score-saver in Physics.

FAQS

Q1. Are these Class 12 Physics important questions enough for Board exam preparation?

Ans. These questions cover the most commonly tested concepts, but you should also revise NCERT examples, derivations, and numerical exercises for complete preparation.

Q2. Do these important questions include numerical and derivation-based problems?

Ans. Yes. They include a balanced mix of numericals, conceptual questions, derivations, and application-based questions from all major chapters.

Q3. Should I write full answers while practising, or is reading enough?

Ans. You should write full answers, especially for derivations and numericals. Writing improves speed, reduces mistakes, and trains your brain for actual exam conditions.

Q4. What should I do if I find certain questions too difficult?

Ans. Go back to the related NCERT section, revise the concept, and then attempt the question again. For numericals, practise similar problems until the method becomes familiar.

Q5. How can I improve my accuracy in numerical questions?

Ans.  Focus on units, conversions, formula application, step-wise solving, and avoid skipping steps. Most mistakes occur in the substitution or simplification stage.