📡 Chapter 18: Electromagnetic Induction & EM Waves – Constructed Response Questions
Prepared by Muhammad Tayyab, Subject Specialist Physics, Govt Christian High School Daska. Based on PECTAA 2026 syllabus (National Curriculum 2023).
📖 What's Inside: This section covers constructed response questions from Chapter 18 Electromagnetic Induction & EM Waves including speed effect on induced e.m.f., iron core in transformers, photons and solar sails, and why transformers work only on A.C. Each question is presented with a detailed answer as per the official PECTAA 2026 Physics curriculum. Perfect for Punjab Boards (Lahore, Gujranwala, Multan, etc.) and all BISE boards across Pakistan.
📚 Related Resources – Chapter 18
Electromagnetic Induction covers Faraday's law, Lenz's law, A.C. generators, transformers, cathode rays, CRO, and EM waves.
📝 Constructed Response Questions & Answers (PECTAA 2026)
18.1 If a magnet is moved quickly into a coil, a larger e.m.f. is induced. Why does speed affect the magnitude of the induced current?
When the magnet is moved more quickly, the magnetic flux changes at a faster rate. According to electromagnetic induction, a faster change in magnetic flux produces a larger induced e.m.f. As a result, a larger induced current flows in the circuit.
✅ Faster change in flux → Larger induced e.m.f. → Larger current.
18.2 Why is an iron core used in transformers instead of wood or plastic? Explain briefly.
An iron core is used because it carries the changing magnetic field efficiently from the primary coil to the secondary coil. Wood and plastic are non-magnetic materials, so they cannot transfer the magnetic field effectively.
✅ Iron core efficiently transfers magnetic field; wood/plastic cannot.
18.3 How does the concept of photons help explain the working of solar sails in space?
Light consists of photons, which carry energy and momentum. When photons strike a solar sail, they exert a small force called radiation pressure, which gradually pushes the spacecraft forward without using fuel.
✅ Photons carry momentum → Exert radiation pressure → Push spacecraft.
18.4 Why can a transformer work only on alternating current and not on direct current?
A transformer works only with alternating current (A.C.) because A.C. produces a changing magnetic field, which induces voltage in the secondary coil. Direct current (D.C.) produces a constant magnetic field, so no induced e.m.f. is generated after the initial moment.
✅ A.C. = Changing magnetic field → Induces voltage. D.C. = Constant field → No induction.
📐 Key Formula – Transformer
\(\frac{V_s}{V_p} = \frac{N_s}{N_p}\)
Turns-Ratio Equation
Unit 10Thermal Physics
Unit 11Transfer of Thermal Energy
Unit 12Waves
Unit 13Sound
Unit 14Light
Unit 15Electrostatics
Unit 16Electricity
Unit 17Electromagnetism
Unit 18✨ Electromagnetic Induction & EM Waves
Unit 19Electronics
Unit 20Atomic and Nuclear Physics
Unit 21Space and Environment
📖 Complete syllabus coverage for Class 10 Physics (PECTAA 2026) – Units 10 to 21
💡 Exam Tip:
For constructed response questions, write clear, logical answers with proper reasoning. Use key terms like "electromagnetic induction", "magnetic flux", "radiation pressure", and "changing magnetic field" as they are commonly tested in exams. These questions follow the PECTAA 2026 pattern and are prepared by Subject Specialist Muhammad Tayyab.
Created by Hira Science Academy | Aligned with PECTAA 2026 Syllabus