CBSE Class 12th Physics Notes – Electric Field
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Physics notes for class 12 Electric Field: The region in which a charge experiences a force is called an electric field.
Electric Field Strength: Electric field strength at a point is vector quantity and is defined as the force experienced by unit positive charge placed at that point and whose direction is along direction of force.
The electric field strength due to a point charge q at a distance r is
E = q/4Π£0 r2
The unit ofElectric field strength is Newton/Coulomb.
Electric Field Lines:The path along which a unit positive charge would move if it is free to do so.
Properties of Electric Field Lines:
- Electric field lines start at positive charge and end at negative charge. For an isolated single charge electric field lines start or end at infinity.
- Two electric field lines never intersect each other.
- In a charge free region electric field lines have no break or they are continuous.
- In a uniform electric field, electric field lines are parallel.
- The number density of electric field lines at a point gives the strength (intensity) of
electric field at that point.
- Electric field lines do not form closed loops.
- The tangent drawn to the electric field line at a point gives the direction of the electric field at that point.
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Electric field lines due to an isolated positive charge
Electric field lines due to an isolated negative charge
Electric field lines due to pair of equal and opposite charges
Electric field lines due to two positive charges
Question: Two electric field lines never intersect. Why?
Ans: If two electric field lines intersect at a point, then there will be two directions for electric field at that point. But this is not possible. So, two electric field lines never intersect each other.