Notes from Toppers
Force and Torque Due To Magnetic Field
1. Magnetic Force:
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Lorentz Force
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key concepts: Definition, mathematical expression (F = qvB sinθ), direction using the right-hand rule, force on a positive and negative charge.
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Examples: Motion of a charged particle in a magnetic field.
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Magnetic Force on a Moving Charge:
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key Concepts: Force experienced by a moving charge in a magnetic field, explanation using Lorentz force equation.
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Examples: Trajectory of a charged particle in a magnetic field.
- Magnetic Force on a Current Carrying Conductor:
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key Concept: Force acting on a current-carrying conductor placed in a magnetic field, direction using Fleming’s left-hand rule.
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Examples: Forces on a straight conductor, a circular loop.
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Magnetic force between two current-carrying conductors:
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key concepts: Parallel and perpendicular conductors, attractive and repulsive forces, concept of magnetic field lines.
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Examples: Calculation of force between various configurations.
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Magnetic force on a Magnetic Dipole:
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key concepts: Magnetic dipole moment, torque experienced by a magnetic dipole in a magnetic field.
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Examples: Potential energy of a magnetic dipole, bar magnet suspended in a magnetic field.
2. Magnetic Field:
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Magnetic field due to a current carrying conductor:
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key concepts: Biot-Savart law, mathematical expression for the magnetic field, field due to straight wire, circular loop, solenoid.
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Examples: Calculating the magnetic field at various points.
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** Magnetic Field due to a Solenoid**:
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Reference: NCERT class 12, chapter - Magnetic Effects of Current and Magnetism
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Key concepts: Solenoid as a long coil, field inside and outside a solenoid, comparison with field due to a bar magnet.
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Examples: Magnetic field strength inside a solenoid.
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** Magnetic Field due to a Toroid**:
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key concepts: Toroid as a coil wound in a circular fashion, field inside and outside the toroid.
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Examples: Determination of magnetic field at the center of toroid.
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** Magnetic Field inside a long straight solenoid**:
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Reference: NCERT class 12, chapter - Magnetic effects of current and magnetism.
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Key concepts: Uniform magnetic field inside a long straight solenoid, its magnitude, and direction.
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Examples: Calculating the field strength inside a given solenoid.
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** Magnetic Field due to a bar magnet**:
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Reference: NCERT class 12, chapter - Magnetic Effects of Current and Magnetism.
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Key concepts: Magnetic field lines, field pattern of a bar magnet.
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Examples: Determining the magnetic field at various points around a bar magnet.
3. Magnetic Torque:
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Torque on a Current loop in a magnetic field:
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key concepts: Torque experienced by a current loop, formula for torque (τ = NIAB sinθ), direction using the right-hand rule.
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Examples: Calculation of torque on a rectangular coil, circular loop.
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** Torque on a magnetic dipole in a magnetic field**:
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key concepts: Magnetic dipole moment, torque experienced by a magnetic dipole in a magnetic field, direction using the right-hand rule.
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Examples: Calculating the torque on a bar magnet in a magnetic field.
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** Torque on a conducting rod in a magnetic field**:
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key concepts: Induced emf and current, Lorentz force, torque experienced by a conducting rod, direction using Fleming’s left-hand rule.
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Examples: Calculating the torque on a conducting rod moving perpendicular to a magnetic field.
4. Applications:
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Magnetic Levitation (maglev) Trains:
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism.
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Key concepts: Principle of magnetic levitation, use of superconducting magnets, advantages, and limitations of maglev technology.
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Examples: Real-world maglev train systems.
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Electric Motors and Generators:
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References: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism.
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Key concepts: Basic principle of an electric motor and generator, role of magnetic fields, types of motors (DC and AC), Lenz’s law, induced emf, and back emf.
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Examples: Construction and working of simple DC motors and generators.
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Magnetic Resonance Imaging (MRI):
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key concepts: Basic principle of MRI, use of strong magnetic fields and radio waves, generating 3D images, applications in medicine.
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Examples: MRI procedure and its medical significance.
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Magnetic Compasses:
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key concepts: Principle of magnetic compass, Earth’s magnetic field, magnetic declination, dip angle.
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Examples: Working and importance of magnetic compasses in navigation.
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Magnetic Separation:
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Reference: NCERT Class 11, Chapter - Motion in a plane
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Key concepts: Use of magnetic fields to separate magnetic materials from non-magnetic materials, applications in industries like mining, recycling, and food processing.
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Examples: Magnetic separation of iron ore from impurities.
5. Problem-Solving Techniques:
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Using vector analysis to calculate forces and torques:
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Reference: NCERT Class 11 and Class 12, Various chapters on vectors
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Key concepts: Components of vectors, vector addition, subtraction, and cross-product, applying vector analysis to magnetic force and torque calculations.
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Examples: Calculating the magnetic forces and torques acting on charged particles and current-carrying conductors using vector analysis.
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Applying Right Hand Rule for Forces and Torques:
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Reference: NCERT Class 12, Chapter - Magnetic Effects of Current and Magnetism
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Key concepts: Right-hand rule for determining the direction of magnetic force and torque, visualizing the directions using the thumb, fingers, and palm of the right hand.
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Examples: Applying right-hand rules in various problems involving force and torque calculations.
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Using superposition principle for magnetic fields:
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Reference: NCERT Class 11 and Class 12, Various chapters on vectors
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Key concepts: Superposition principle, calculating magnetic field due to multiple sources like current-carrying wires, solenoids, or bar magnets.
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Examples: Calculating the total magnetic field at a given point due to multiple magnetic sources.
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Solving numerical problems:
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Reference: NCERT Class 11 and Class 12, chapters related to electromagnetism
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Key concepts: Formula-based calculations involving force, torque, magnetic field, magnetic dipole moment, etc.
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Examples: Solving numerical problems on force exerted on moving charges, torque on current loops, magnetic field strength, and magnetic dipole interactions.