# NCERT Solutions for Class 12 Physics Electric Field Notes

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 the direction of the 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 a 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

the 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 the electric field at that point. But this is not possible. So, two electric field lines never intersect each other.

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August 22, 2019