Chapter 5: Magnetism and Matter

the genius April 08, 2026

Magnetism and Matter: Class 12 Physics Chapter 5 Notes in Hindi

Pichle chapter mein humne padha ki kaise behta hua current magnetism paida karta hai. Is chapter mein hum Dharti ke magnetism (Earth's Magnetism) aur alag-alag tarah ke Magnetic Materials ke baare mein jaanenge.

1. The Bar Magnet

Bar magnet ek artificial magnet hai jiske do poles hote hain: North (N) aur South (S).

  • Magnetic Field Lines: Ye hamesha North pole se nikalti hain aur South pole mein enter karti hain (bahar), aur magnet ke andar South se North jati hain (closed loops banati hain).

  • Magnetic Dipole Moment ($m$):

    $$m = q_m \times 2l$$

    (Yahan $q_m$ pole strength hai aur $2l$ magnetic length).

    • Shutterstock

2. Gauss’s Law for Magnetism

Jaise electrostatics mein Gauss law tha, magnetism mein bhi hota hai. Lekin yahan total magnetic flux kisi bhi closed surface se hamesha Zero hota hai.

$$\oint B \cdot dS = 0$$

Reason: Magnetic monopoles exist nahi karte; hamesha North aur South saath mein hote hain.

3. Earth’s Magnetism (Bhu-Chumbakatva)

Hamari dharti bhi ek bade magnet ki tarah behave karti hai. Iske teen main components hote hain jinhe Magnetic Elements of Earth kehte hain:

  1. Magnetic Declination ($\theta$): Geographic meridian aur Magnetic meridian ke beech ka angle.

  2. Magnetic Inclination or Dip ($\delta$): Dharti ka total magnetic field horizontal ke saath jo angle banata hai. (Poles par $90^\circ$ aur Equator par $0^\circ$ hota hai).

  3. Horizontal Component ($B_H$): Earth ke magnetic field ka horizontal direction mein part.

    $$B_H = B \cos \delta$$

4. Classification of Magnetic Materials

Materials ko unki magnetic properties ke basis par teen categories mein baanta gaya hai:

PropertyDiamagneticParamagneticFerromagnetic
ExampleWater, Copper, BismuthAluminum, OxygenIron, Cobalt, Nickel
BehaviorMagnetic field se weakly repel hote hain.Weakly attract hote hain.Strongly attract hote hain.
Susceptibility ($\chi$)Negative aur choti value.Positive aur choti value.Positive aur bahut badi value.

5. Important Terms

  • Magnetization ($M$): Magnetic moment per unit volume.

  • Magnetic Intensity ($H$): Wo magnetic field jo kisi material ko magnetize karne ki kshamta rakhta hai.

  • Curie’s Law: Paramagnetic materials ki susceptibility temperature badhne par kam ho jati hai.

    $$\chi \propto \frac{1}{T}$$

6. Top Important Questions (Chapter 5)

Aapke blog ke liye niche diye gaye questions must-add hain:

Short Questions:

  1. Magnetic field lines closed loops kyun banati hain? Kyunki magnets mein poles ko alag nahi kiya ja sakta (Monopoles don't exist).

  2. Angle of Dip equator par kitna hota hai? Zero ($0^\circ$).

  3. Curie Temperature kya hai? Wo temperature jiske upar ek Ferromagnetic material, Paramagnetic ban jata hai.

Conceptual & Long Questions:

  1. Distinguish between Diamagnetic, Paramagnetic, and Ferromagnetic materials. (Upar di gayi table use karein).

  2. Explain the three elements of Earth's magnetic field with a diagram.

  3. Properties of magnetic field lines. (Board exams ka favourite question).

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