Magnetism and Matter – Class 12 Physics Notes | CBSE NCERT Based

 πŸ“š Chapter: Magnetism and Matter – Class 12 Physics Notes



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πŸ”Έ 1. Introduction


This chapter deals with the magnetic properties of materials, Earth's magnetism, and how magnetism and matter are related.



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πŸ”Ή 2. Bar Magnet


Magnetic dipole has two poles: North and South


Like poles repel, unlike poles attract


Magnetic field lines emerge from North and enter South


Magnetic dipole moment (M):

M = m × 2l

where, m = pole strength, 2l = length of magnet




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πŸ”Ή 3. Magnetic Field Due to a Bar Magnet


At a point on the axial line:


B_{\text{axial}} = \frac{\mu_0}{4\pi} \cdot \frac{2M}{r^3}


At a point on the equatorial line:


B_{\text{equatorial}} = \frac{\mu_0}{4\pi} \cdot \frac{M}{r^3}



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πŸ”Ή 4. Torque on a Magnetic Dipole in Uniform Magnetic Field


\vec{\tau} = \vec{M} \times \vec{B}


Where:


M = Magnetic dipole moment


B = External magnetic field


Direction by right-hand rule




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πŸ”Ή 5. Magnetic Properties of Materials


Type Magnetic Susceptibility (Ο‡) Relative Permeability (ΞΌr) Example


Diamagnetic Ο‡ < 0 ΞΌr < 1 Bismuth, Copper

Paramagnetic Ο‡ > 0 (small) ΞΌr > 1 Aluminum, Platinum

Ferromagnetic Ο‡ ≫ 0 ΞΌr ≫ 1 Iron, Cobalt, Nickel




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πŸ”Ή 6. Hysteresis Loop (Ferromagnets)


It shows how magnetization changes with applied magnetic field.


Retentivity: Residual magnetism


Coercivity: Reverse field needed to demagnetize



Area of loop = energy loss per cycle



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πŸ”Ή 7. Earth's Magnetism


Earth behaves like a giant bar magnet


Magnetic field lines emerge from near geographic south and enter geographic north



Terms:


Magnetic Declination: Angle between geographic and magnetic meridian


Magnetic Inclination (Dip): Angle between magnetic field and horizontal


Horizontal Component (Bh):

Bh = B cos(ΞΈ)




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πŸ“Œ Conclusion:


This chapter builds your understanding of how materials respond to

 magnetic fields and helps in concepts related to Earth's magnetism, useful in navigation and technology.

πŸ“Š Important Diagrams – Magnetism and Matter (Class 12 Physics)



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πŸ”Ή 1. Magnetic Field Lines of a Bar Magnet


Show how field lines emerge from the north pole and enter the south pole


Very common 2-mark diagram




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πŸ”Ή 2. Earth as a Magnet


Earth’s magnetic field lines


Magnetic axis and geographic axis


Magnetic equator and poles




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πŸ”Ή 3. Magnetic Declination and Inclination


Diagram showing:


Magnetic meridian


Geographic meridian


Angle of declination (D)


Angle of dip/inclination (I)





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πŸ”Ή 4. Hysteresis Loop


Magnetization (M or B) vs Magnetic field (H) graph


Shows:


Retentivity


Coercivity


Area = energy loss





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πŸ”Ή 5. Magnetisation Curve


Shows behavior of diamagnetic, paramagnetic, and ferromagnetic materials


Often asked to compare magnetic behavior




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πŸ”Ή 6. Bar Magnet as Equivalent Solenoid


Explains how a bar magnet behaves like a

 current-carrying solenoid


Magnetic field lines inside and outside shown


✍️ Written by: Shahid – Study with Shahid

πŸ”— Visit: https://shahidnotes12.blogspot.co

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