🧲 Chapter 17: Electromagnetism – Constructed Response
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 17 Electromagnetism including Oersted's discovery about the connection between electricity and magnetism, the role of the split ring commutator in a D.C motor, and the effect of angle on the magnetic force on a conductor. Each question is presented with a reasoned 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 17: Electromagnetism
Electromagnetism covers magnetic fields, right-hand grip rule, force on conductors, D.C motor, relay, loudspeaker, and Earth's magnetic field.
📝 Constructed Response Questions & Answers (PECTAA 2026)
17.1 Why does a magnetic field form around a conductor when current flows through it, but not when the current is OFF? What does this reveal about the nature of electricity and magnetism?
Answer: According to Hans Christian Oersted, a steady electric current in a conductor generates a magnetic field around it. When the current is OFF, there is no movement of charges, so no magnetic field is produced.
This shows that electricity and magnetism are fundamentally connected, as moving charges (electric current) produce magnetic fields.
✅ Moving charges (electric current) produce magnetic fields, revealing the fundamental connection between electricity and magnetism.
17.2 In a D.C motor, why does the coil stop turning after \(90^\circ\) if the direction of the current is not reversed? What mechanical feature solves this issue?
Answer: Without reversing the current, the forces acting on the sides of the coil push it into a vertical position, making the coil perpendicular to the magnetic field. At this point, the net force becomes zero, so the coil stops rotating.
This problem is solved by a split ring commutator, which reverses the direction of current after every half turn, allowing the coil to rotate continuously.
✅ Split ring commutator reverses current after every half turn, ensuring continuous rotation.
17.3 How does placing a wire at different angles to a magnetic field affect the magnetic force it experiences, and why is this important in designing motors?
Answer: The magnitude of the force on a current-carrying conductor is given by: \(F = ILB \sin \theta\).
The force is maximum when the wire is perpendicular to the magnetic field (\(\theta = 90^\circ\)) and zero when it is parallel (\(\theta = 0^\circ\)).
This is important in designing motors because the coil is arranged to experience maximum force (torque), ensuring efficient rotation.
✅ Force is maximum at \(\theta = 90^\circ\) and zero at \(\theta = 0^\circ\); motors are designed for maximum torque.
🧲 Key Concepts – Electromagnetism
Force on a Conductor: \( F = ILB \sin \theta \)
Oersted's Discovery: Moving charges (electric current) produce magnetic fields.
D.C Motor: Split ring commutator reverses current every half turn for continuous rotation.
Unit 10Thermal Physics
Unit 11Transfer of Thermal Energy
Unit 12Waves
Unit 13Sound
Unit 14Light
Unit 15Electrostatics
Unit 16Electricity
Unit 17✨ Electromagnetism
Unit 18Electromagnetic 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, provide clear reasoning and explanations. Use key terms like "Oersted's discovery", "split ring commutator", and "\(F = ILB \sin \theta\)" 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