Moving Charges and Magnetism – Class 12 Physics Notes | CBSE NCERT Based
📚 Chapter: Moving Charges and Magnetism – Class 12 Physics Notes
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🔸 1. Magnetic Force on a Moving Charge
When a charged particle moves in a magnetic field, it experiences a force:
\vec{F} = q (\vec{v} \times \vec{B}) = qvB \sin\theta
Maximum force when
No force when particle is at rest or
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🔹 2. Magnetic Force on a Current-Carrying Conductor
\vec{F} = I (\vec{L} \times \vec{B})
Direction of force: given by Right-Hand Rule
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🔹 3. Motion of a Charged Particle in Magnetic Field
Path becomes circular if velocity is perpendicular to B.
Radius of circular path:
r = \frac{mv}{qB}
Time period:
T = \frac{2\pi m}{qB}
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🔹 4. Biot–Savart Law
Gives magnetic field due to a current element:
d\vec{B} = \frac{\mu_0}{4\pi} \frac{I d\vec{l} \times \vec{r}}{r^3}
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🔹 5. Magnetic Field Due to:
Straight wire:
B = \frac{\mu_0 I}{2\pi r}
Circular loop:
B = \frac{\mu_0 I}{2R} \quad \text{(at center)}
Solenoid:
B = \mu_0 n I
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🔹 6. Ampere’s Circuital Law
\oint \vec{B} \cdot d\vec{l} = \mu_0 I_{enclosed}
Used to calculate magnetic field in symmetrical situations.
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🔹 7. Lorentz Force
When both electric and magnetic fields are present:
\vec{F} = q (\vec{E} + \vec{v} \times \vec{B})
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🔹 8. Cyclotron
A device to accelerate charged particles using magnetic field and alternating voltage.
Cyclotron frequency:
f = \frac{qB}{2\pi m}
Used in medical and nuclear fields.
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🔹 9. Torque on Current Loop in Magnetic Field
\vec{\tau} = \vec{m} \times \vec{B}
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🔹 10. Magnetic Dipole in Uniform Magnetic Field
Experiences torque, aligns itself
No net force, only rotation
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📌 Conclusion:
This chapter connects electricity and magnetism. It explains how moving charges generate magnetic fields, and how magnetic fields affect current and charges — formin
g the base of electromagnetism.
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✍️ Written by: Shahid – Study with Shahid
🔗 Visit: https://shahidnotes12.blogspot.com
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