Class 12 physics chapter 1 Electric field and charges
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Class 12 physics chapter 1
Institution
Class 12 physics notes chapter 1 provides a comprehensive introduction to the fundamental concepts of electric charges and electric fields. The chapter begins with a discussion on electric charges and their properties, including the quantization of charge and the concept of Coulomb's law. Coulomb's...
1. Electric Charges: There are two types of electric charges, positive and negative. Like charges
repel each other, while opposite charges attract each other. Electric charge is conserved in a
closed system.
2. Conductors and Insulators: A conductor is a material that allows charges to move freely
through it, while an insulator is a material that does not allow charges to move easily. Metals
are good conductors while rubber, glass, etc. are insulators.
3. Charging by Induction: A charged object can induce a temporary charge on another object
without direct contact. The process is called charging by induction. The object that gets
charged is called an induced charge.
4. Coulomb's Law: Coulomb's law states that the force between two point charges is
proportional to the product of their magnitudes and inversely proportional to the square of
the distance between them. The force is also along the line joining the charges.
F = k(q₁q₂)/r²
Where:
F is the electrostatic force between two charged particles,
Q₁ and q₂ are the magnitudes of the charges of the two particles,
R is the distance between the two particles, and
K is Coulomb’s constant, which is approximately equal to 9 x 10^9 N m²/C².
The direction of the force vector is along the line joining the two charges, and is attractive if the
charges are of opposite sign and repulsive if they are of the same sign.
Here are some point-wise properties of Coulomb’s law:
1. Coulomb’s law describes the electrostatic force between two charged objects.
2. The force is proportional to the product of the charges and inversely proportional to the
square of the distance between them.
, 3. The force is attractive for opposite charges and repulsive for like charges.
4. The proportionality constant in Coulomb’s law is known as the Coulomb constant.
5. The SI unit of charge is Coulomb (C) and the SI unit of force is Newton (N).
6. Coulomb’s law applies to point charges, but can also be used to describe the force between
charged objects of finite size.
7. Coulomb’s law can be used to calculate the electric field generated by a charge distribution.
8. Coulomb’s law is valid in both vacuum and in materials such as insulators and conductors.
9. Coulomb’s law is one of the fundamental laws of physics and is used in many applications,
including electronics, telecommunications, and electrochemistry.
10. Coulomb’s law is closely related to the concept of electric potential and can be used to
calculate the potential energy of a charged system.
5. Electric Field: The electric field is a region in which an electric charge experiences a force. It
is a vector quantity and is denoted by E. The direction of the electric field is the direction of
the force that a positive charge would experience if placed in the field.
The formula for the electric field (E) at a point in space due to a stationary point charge Q is:
E = k * Q / r^2
Where k is the Coulomb constant (k = πε0), r is the distance between the point charge and
the point in space, and Q is the magnitude of the point charge.
If there are multiple point charges, you can find the electric field at a point in space due to all of
them by adding up the electric fields from each individual point charge vectorially.
6. Electric Field Lines: Electric field lines are used to represent the direction and strength of an
electric field. The density of the lines represents the strength of the field, and the direction of
the lines gives the direction of the field. Electric field lines always start from a positive charge
and end at a negative charge.
Electric field lines are used to represent the direction and strength of the electric field at different
points in space.
The properties of electric field lines include:
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