Question

Electric field varies r^-3 due to:
a) a point charge
b) an infinite line charge
c) an electric dipole
d) an infinite plane sheet of charge


Choose the correct answer....answer first pls...​

Answer 1

Answer:

c

Explanation:

it is electricity that varies

Answer 2

Answer:

Electric field varies r^-3 due to: c) an electric dipole

Explanation:

Electric Dipole: An electric dipole forms when two equal and opposite charges (+q and -q) are separated by a distance 2a.

• Total charge of an electric dipole is 0.
• The mid-point of locations of –q and q is called the center of the dipole.
• The direction of dipole is from -q to +q.

The derivation of Electric field at a point(p) on the axis from the dipole: The point is at r distance on the side of +q charge

• Formula for electric field for +q charge, E(+q) = q/4π∈(r-a)²
• Formula for electric field for -q charge, E(-q) = -q/4π∈(r+a)²
• Total electric field, E =  E(+q) + E(-q) = q/4π∈ ( $\frac{1}{(r-a)^2}$ - $\frac{1}{(r+a)^2}$)

                                                                 =    $\frac{q*4ar}{(r^2-a^2)^2}$ x4π∈

• Now if r >> a, E = 4qa/4π∈r³

                                E ∝ $\frac{1}{r^3}$

So we can say for dipole electric field varies with $r^-3$.