by Is the paper tougher?
If you are appearing for the 2026 Board Exams, you already know the big update: 50% of the paper is now Competency-Based. This means rote memorizing derivations for Alternating Current (AC) is no longer enough. You need to understand how LCR circuits behave in real life.
In this guide, we have curated the most important Alternating Current questions (2019-2025), but with a twist: we have analyzed them according to the new 2026 Exam Blueprint to help you study smarter, not harder.
⚠️ Teacher’s Note for the 2026 Batch
From the Desk of Physics Q&A:
While compiling these questions, we noticed a clear trend: CBSE is moving away from “Derive the expression for Impedance” to questions like “What happens to the bulb’s brightness if…”.
Our Advice: Use the PYQs below to build your foundation, but focus heavily on the “Predicted Case Study” section at the end of this post. That is where the 2026 marks are hidden.
Once you master AC circuits, the logical next step is to understand Displacement Current (Chapter 8) which connects electricity and magnetism.
Struggling with the concept of Potential Difference? You might need to revise these essential Electrostatics questions before solving LCR circuits.
Need more mathematical practice? Browse our full library of solved numerical problems for JEE and Boards.
1. 2026 “Must-Do” Conceptual Questions (Competency-Based)
These questions test your understanding, not your memory. (Highly probable for Section A & B).
Q1: The Frequency Trap (Application)
An AC source of voltage V = V₀ sin ωt is connected to a series LCR circuit. If the frequency of the source is doubled, how does the impedance change in an (a) Inductive-only circuit and (b) Capacitive-only circuit?
Teacher’s Hint: Remember that XL ∝ f (direct) while XC ∝ 1/f (inverse). Don’t just write the formula; explain the behavior.
Q2: The “Bulb Brightness” Logic
A light bulb and an inductor are connected in series to an AC source. An iron rod is inserted into the inductor. What happens to the brightness of the bulb?
Why this matters for 2026: This is a classic “qualitative” question. Inserting iron increases L → increases XL → decreases Current → Bulb dims.
According to the latest curriculum updates on the official CBSE Academic website, the weightage for competency questions has increased.
2. Important Derivations (2019–2025 PYQs)
Even with the new pattern, 30% of the paper will still be direct theory. These are the most repeated derivations.
Top Priority: Series LCR Circuit
- (2025, 2020) Draw the phasor diagram for a series LCR circuit and derive the expression for Impedance (Z).
- (2024) Obtain the condition for Resonance. What is the power factor at resonance?
Pro Tip: Visualize how resonance works using this Circuit Construction Kit (AC) by PhET Colorado. It helps in understanding the phase difference visually.
Top Priority: The Transformer
- (2024) Explain the working of a step-up transformer. Why can’t a transformer work on DC?
- (2023) List four main causes of energy loss in a real transformer and how to minimize them.
💡 Quick Tip: For the “Energy Loss” question, don’t just list “Eddy Currents.” You must add the solution: “Minimized by using laminated cores.”
3. 🏆 Predicted Case Study for 2026 (New Pattern)
Section E of your 2026 paper will likely have a case study on Transformers or Resonance. Here is our prediction:
Case Study: Long-Distance Power Transmission
A power plant generates electricity at 440V. To transport this power to a city 200km away, a step-up transformer increases the voltage to 11,000V. At the city substation, it is stepped down for domestic use.
Questions to practice:
- Why is high voltage preferred for transmission? (Concept: I²R Loss)
- If the transformer is assumed to be 100% efficient, what is the ratio of currents in the primary vs secondary coils?
Need Help with the Numericals?
Reading the question is one thing, but solving it under exam pressure is another. We break down the toughest 2025 Numerical problems step-by-step on our Instagram.
📸 Follow @physics_qanda for Daily Solutions
Good luck with your prep! Bookmark this page—we will update it with the Official CBSE Sample Paper analysis as soon as it releases.
