Electric charges and field ncert part2

Part2
Coulomb’s Law
Coulomb’s law describes the electrostatic force between two point charges. If two stationary point charges Q1 and Q2 are placed a distance r apart, the magnitude of the electrostatic force F between them is given by:
Key Points:
Direction of Force: The force acts along the line joining the two charges.
Nature of Force:
Repulsive: If the charges are of the same sign (both positive or both negative).
Attractive: If the charges are of opposite signs (one positive and one negative).
Conservative Nature: The electrostatic force is conservative, meaning that the work done in moving a charge between two points is independent of the path taken.
Inverse Square Law: The force follows the inverse square law, meaning the force decreases with the square of the distance between the charges.
Forces Between Multiple Charges
When dealing with multiple charges, Coulomb’s law applies to the interaction between any two charges. However, calculating the net force on a specific charge in the presence of several other charges requires a different approach.
The net force on a charge due to multiple other charges is determined by taking the vector sum of all the individual forces exerted on that charge by each of the other charges, considered one at a time. This principle is known as the superposition principle.
Superposition Principle
The superposition principle states that the interaction between any two charges is not influenced by the presence of other charges. In simpler terms if you have multiple charges in a system the force between any two specific charges remains the same, regardless of other charges in the vicinity.
Properties of Electric Field Lines
Electric field lines have several key properties that help visualize the behavior of electric fields:
Continuous Curves: Electric field lines form continuous curves without any breaks in regions where there are no charges. This continuity shows the direction of the field at every point in space.
No Intersection: Two electric field lines never cross each other. If they did, it would imply that the electric field has two different directions at the same point, which is impossible.
Starting and Ending Points: Electric field lines originate from positive charges and terminate on negative charges. This indicates the direction of the force that a positive test charge would experience in the field.
Starting and Ending Points: Electric field lines originate from positive charges and terminate on negative charges. This indicates the direction of the force that a positive test charge would experience in the field.
No Closed Loops: Electrostatic field lines never form closed loops. They always start on a positive charge and end on a negative charge, or they extend to infinity if no negative charge is present. This distinguishes electric fields from magnetic fields, where lines can form closed loops.
Electric Flux
Electric flux refers to the total number of electric field lines passing through a given area. It doesn’t involve a physical flow like liquids but is a measure of how strong the electric field is over that area.

The electric flux Δθ through a small area element ΔS is given by:

Δθ= E.ΔS= E ΔS cosθ

Here:

E is the electric field strength,
ΔS is the area element,
θ is the angle between the electric field E and the normal (perpendicular) to the area element ΔS
Electric Dipole
An electric dipole is a system of two equal and opposite charges, typically denoted as +q and −q separated by a certain distance. The dipole moment is calculated as the product of the magnitude of one of the charges and the distance separating them, mathematically expressed as:

p=q×2a

Here, 2a represents the distance between the charges, and the direction of the dipole moment vector is from the negative charge to the positive charge. The concept of an electric dipole is important in understanding how molecules and other systems interact with electric fields.

Charge on a Capacitor
The net charge on a capacitor is always zero because the charges on its two plates are equal in magnitude but opposite in sign. However, when we talk about the charge Q on a capacitor, we refer to the magnitude of the charge on one of the plates.