In: Physics
What does "Electric potential is the negative line integral of electric field" mean?
The multiplication of electric
field and the path length gives Line integral of electric
Field.
Let there be two point A and B on a non uniform electric field
(magnitude and direction at every point is different). The
irregular line denotes the path travelled by charge. With changing
Electric field, the path travelled by a charge also changes at
every point on the curve.
To find line integral at every point, take a very small length
dl on the path. So that dl makes a certain angle θ with the
electric field. On resolving dl into two components as dlcosθ and
dlsinθ the component
of dl along E is dl cosθ. As shown in figure.
Potential difference dV = Edr.
So line integral to move charge from A to B = A∫BEdrCosθ
VA - VB = A∫B E→.dr→
To move charge from B to A (VA - VB) = - B∫AE→.dr→
In a variable electric field, potential difference between two point is equal to negative of line integral of electric field.