Class 12th Physics,/ Board Exam में हर साल पूछे जाने आने प्रश्न || Physics Most Important Questions

Summary

This revision session offers a comprehensive overview of key physics concepts related to magnetism and electromagnetism. The speaker discusses important topics like current density, Lorentz force, Biot-Savart law, and electromagnetic induction. Emphasis is placed on critical formulas and laws such as Faraday's Law, Lenz's Law, and electrical resonance, with practical tips for exam preparation. The speaker advises focusing on definitions and properties of magnetic materials while highlighting the importance of diagramming and understanding key principles for achieving high marks in exams. The session encourages consistent study and confidence in tackling physics problems.

Takeaways

• 😀 Focus on understanding core concepts like current density and formulas such as j = i / A.
• 😀 Always remember key formulas like F = q * v * B * sin(θ) for magnetic force calculations.
• 😀 Master Bio-Savart's law and its applications for calculating magnetic fields from current-carrying conductors.
• 😀 Lenz's Law is crucial: it states that the direction of induced current opposes the cause of its generation, and it follows the principle of conservation of energy.
• 😀 Pay close attention to differences between diamagnetic, paramagnetic, and ferromagnetic materials for exam questions.
• 😀 For alternating current, focus on its definition and the conditions for resonance in LCR circuits.
• 😀 Electromagnetic induction involves the generation of current in a coil when there's relative motion between the coil and a magnetic field.
• 😀 Study the practical applications of Faraday’s Law and self-induction vs mutual induction to understand how current is induced in coils.
• 😀 Diagrams, especially in laws like Bio-Savart and magnetic field concepts, should be drawn with a pencil for better marks.
• 😀 Revision should focus on the most repeated definitions and concepts such as current density, Faraday’s Law, Lenz’s Law, and self-induction to boost exam performance.

Q & A

What is the formula for current density?

The formula for current density is j = i / A, where i is the current flowing through a conductor, and A is the cross-sectional area of the conductor.

What is the difference between current and current density?

Current is the total charge flowing through a conductor per unit time, while current density refers to the amount of current flowing per unit area of the conductor.

What does Lorentz force represent and how is it calculated?

Lorentz force represents the force exerted on a charged particle moving in a magnetic field. It is calculated using the formula F = q * v * B * sin(θ), where q is the charge, v is the velocity of the particle, B is the magnetic field, and θ is the angle between the velocity and the magnetic field.

What is Bio-Savart's law and its significance?

Bio-Savart's law provides the magnetic field at a point due to a small segment of current-carrying conductor. The law is crucial in calculating the magnetic field produced by complex current configurations. The formula is dB = (μ₀ / 4π) * (I * dl × r) / r², where μ₀ is the permeability of free space, I is the current, dl is the infinitesimal length of the conductor, r is the distance from the point of interest, and r² is the square of that distance.

How do the Left Hand and Right Hand Rules relate to magnetic fields?

The Left Hand Rule helps determine the direction of force on a current-carrying conductor in a magnetic field, while the Right Hand Rule is used to determine the direction of the magnetic field around a current-carrying conductor.

What is the definition of alternating current (AC)?

Alternating current (AC) is an electric current that reverses its direction periodically and whose magnitude changes with time. It operates at a fixed frequency.

What is the significance of Lenz's law in electromagnetic induction?

Lenz's law states that the direction of the induced current is always such that it opposes the cause (change in magnetic flux) that produces it. This principle is based on the conservation of energy.

What is the main difference between self-induction and mutual induction?

Self-induction refers to the phenomenon where a change in current in a coil induces an electromotive force (EMF) in the same coil, while mutual induction occurs when a change in current in one coil induces an EMF in a nearby coil.

What does the term 'electromagnetic induction' refer to?

Electromagnetic induction is the process by which a change in magnetic flux through a coil or loop induces an electromotive force (EMF) and consequently an electric current in the coil.

What are some key differences between diamagnetic and paramagnetic materials?

Diamagnetic materials are repelled by magnetic fields and do not retain magnetic properties when the external field is removed. Paramagnetic materials are weakly attracted by magnetic fields and can become magnetized when exposed to a magnetic field.