Question 1

Which of the following best describes an electric dipole?

Accepted Answer

Two equal and opposite charges separated by a fixed distance.

Question 2

What is the expression for the electric dipole moment $\mathbf{p}$?

Accepted Answer

$\mathbf{p} = q \cdot d$

Question 3

For a point located on the perpendicular bisector of a dipole, what is the approximate electric field at distance $r$ (where $r \gg d$)?

Accepted Answer

$E = \frac{p}{4\pi\epsilon_0 r^3}$

Question 4

Which principle is used to calculate the electric field at a point due to a dipole?

Accepted Answer

Superposition principle

Question 5

The electric field at a point on the axis of a dipole (where $r \gg d$) is:

Accepted Answer

$E = \frac{p}{2\pi\epsilon_0 r^3}$

Question 6

If the dipole moment $\mathbf{p}$ is directed along the $+y$ axis, what is the direction of the electric field at a point far along the $+y$ axis?

Accepted Answer

Along $+y$ axis

Question 7

Which equation is valid for the electric field at a point on the perpendicular bisector of a dipole?

Accepted Answer

$E = \frac{p}{4\pi\epsilon_0 r^3}$

Question 8

The African knifefish uses its electric dipole to:

Accepted Answer

Sense its environment and detect prey

Question 9

For a dipole, the electric field at a distance $r$ much greater than the dipole size $d$ varies as:

Accepted Answer

$1/r^3$

Question 10

If the dipole consists of charges $+q$ and $-q$ separated by distance $d$, what is the value of $p$?

Accepted Answer

$p = qd$

Question 11

Which mathematical technique is used to approximate the electric field at points far from the dipole?

Accepted Answer

Binomial expansion

Question 12

A dipole is centered at the origin with $\mathbf{p}$ along the $+y$ axis. What is the approximate electric field at a point $y$ on the $+y$ axis, where $y \gg d$?

Accepted Answer

$E = \frac{p}{2\pi\epsilon_0 y^3}$

Question 13

Why is the electric field along the axis of a dipole twice as strong as the field at the same distance on the perpendicular bisector?

Accepted Answer

Because the vector addition of fields is constructive along the axis.

Question 14

Which of the following is NOT a correct statement about electric dipoles?

Accepted Answer

The field is uniform everywhere.

Question 15

In the context of the knifefish, what real-world application does the dipole field provide?

Accepted Answer

It enables the fish to sense objects in its environment.

Question 16

If $\epsilon_0$ is the permittivity of free space, what is the value of $k$ in the dipole field equations?

Accepted Answer

$k = \frac{1}{4\pi\epsilon_0}$

Question 17

A dipole is placed in water, which has a higher permittivity than air. How does the electric field at a given distance change?

Accepted Answer

The field decreases because $\epsilon_0$ is larger.

Question 18

Which scenario best illustrates the use of the superposition principle in dipole field calculation?

Accepted Answer

Adding the fields from the positive and negative charges at a point.

Question 19

If the distance between the charges in a dipole is doubled, what happens to the dipole moment $p$?

Accepted Answer

It is doubled.

Question 20

Which of the following is a correct expression for the electric field at a point $P$ on the perpendicular bisector of a dipole?

Accepted Answer

$E = \frac{p}{4\pi\epsilon_0 r^3} \hat{i}$

Electric Dipole and Its Electric Field

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