Bihar Board - Class 12 Physics - Chapter 1: Electric Charge and Field Handwritten Notes

Electric charge is a fundamental property of matter that causes it to experience a force when placed in an electric field. This chapter explores the nature of electric charges, Coulomb's law, the concept of an electric field, and the behavior of charges in different scenarios. It forms the foundation for understanding various electrical phenomena in physics.

Key Points

1. Electric Charge

   • Definition: A property of matter responsible for electrical interactions. It can be positive or negative.
   • Types:
     • Like charges repel; unlike charges attract.
     • Charges are quantized and conserved. The smallest charge is $e = 1.6 \times 10^{-19} \, \text{C}$.
   • Conductors allow free movement of charges, while insulators do not.

2. Coulomb's Law

   • States the force between two point charges is directly proportional to the product of their charges and inversely proportional to the square of the distance between them:
     $F = k \frac{q_1 q_2}{r^2}$
     where $k = 9 \times 10^9 \, \text{Nm}^2/\text{C}^2$.

3. Electric Field

   • Definition: A region around a charge where another charge experiences a force.
   • Electric Field Intensity ($E$):
     $E = \frac{F}{q} = k \frac{q}{r^2}$
     • It is a vector quantity with direction determined by the force on a positive test charge.
   • Field Lines: Imaginary lines that represent the direction of the electric field. They start from positive charges and end on negative charges.

4. Electric Dipole

   • A pair of equal and opposite charges separated by a distance.
   • Dipole moment ($p$) is given by $p = q \cdot d$, where $q$ is the charge and $d$ is the separation distance.
   • The electric field of a dipole is different along axial and equatorial positions.

5. Electric Flux

   • Measures the number of electric field lines passing through a surface.
   • Given by $\Phi_E = \vec{E} \cdot \vec{A}$, where $\vec{A}$ is the area vector.
   • Gauss's law states that the total electric flux through a closed surface is proportional to the enclosed charge:
     $\Phi_E = \frac{q_{\text{enclosed}}}{\epsilon_0}$

6. Applications and Importance

   • Understanding charges and fields is crucial in designing electrical devices, capacitors, and circuits.
   • Plays a role in explaining natural phenomena like lightning and the behavior of materials in electric fields.

Conclusion

The concepts of electric charge and field are fundamental to understanding electromagnetism and its applications in technology and nature. Coulomb's law, electric field, and Gauss's law provide essential tools for analyzing electrical interactions and their effects.

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