Q: A water molecule has a dipole moment of $6.16 \times 10^{-30}$ C·m. What is the magnitude and direction of the electric field at $x = 3.00 \times 10^{-9}$ m along the axis of the dipole?

$4.1 \times 10^6$ N·C$^{-1}$ along the positive x-axis

Question 1

Two point charges, $-Q$ and $+4Q$, are placed along the x-axis as shown. At which position(s) marked A-G is the electric field zero?

Accepted Answer

At a point to the left of $-Q$ (position A)

Question 2

Given two charges $+Q$ and $-Q$ arranged as shown, what happens to the magnitude of the electric field at point P if the $-Q$ charge is replaced by $+Q$?

Accepted Answer

The magnitude remains the same

Question 3

Three charges are placed at equal distances from the origin: one $+2q$ at the top and two $+q$ symmetrically at the bottom. What is the direction of the net electric field at the origin?

Accepted Answer

Upward, along the y-axis

Question 4

Which equation correctly gives the magnitude of the electric field produced by a point charge $q$ at a distance $r$?

Accepted Answer

$E = \frac{1}{4\pi\epsilon_0} \frac{q}{r^2}$

Question 5

A water molecule has a dipole moment of $6.16 	imes 10^{-30}$ C·m. What is the magnitude and direction of the electric field at $x = 3.00 	imes 10^{-9}$ m along the axis of the dipole?

Accepted Answer

$4.1 	imes 10^6$ N·C$^{-1}$ along the positive x-axis

Question 6

Which of the following statements about electric field lines is FALSE?

Accepted Answer

Electric field lines can cross each other

Question 7

For a dipole with charges $+q$ and $-q$ separated by distance $s$, what is the magnitude of the dipole moment vector?

Accepted Answer

$p = qs$

Question 8

At a far distance $r$ from the center of a dipole, what is the magnitude of the electric field along the axis of the dipole?

Accepted Answer

$E = \frac{1}{4\pi\epsilon_0} \frac{2p}{r^3}$

Question 9

Which real-world scenario best illustrates the concept of an induced electric dipole?

Accepted Answer

A neutral atom placed in a strong external electric field

Question 10

If the electric field at a point is zero due to two charges, what must be true about the magnitudes and directions of the fields from each charge at that point?

Accepted Answer

The fields must be equal in magnitude and opposite in direction

Question 11

A lightning strike is associated with a large electric field due to charge separation. Which of the following is a direct consequence of this phenomenon?

Accepted Answer

The air becomes ionized, allowing current to flow

Question 12

Which of the following best describes the direction of the dipole moment vector for a dipole consisting of $+q$ and $-q$?

Accepted Answer

From the negative charge to the positive charge

Question 13

If two positive charges are placed symmetrically about the y-axis and a third positive charge is placed on the y-axis above the origin, what is the direction of the net electric field at the origin?

Accepted Answer

Upward along the y-axis

Question 14

Which of the following is NOT a property of electric field lines?

Accepted Answer

They can form closed loops

Question 15

A dipole is placed at the origin with its axis along the x-axis. At a point far away on the x-axis, what is the direction of the electric field?

Accepted Answer

Along the positive x-axis

Question 16

Which formula gives the magnitude of the electric field at a point on the axis perpendicular to a dipole at distance $r$?

Accepted Answer

$E = \frac{1}{4\pi\epsilon_0} \frac{p}{r^3}$

Question 17

If the sign of a charge is reversed, how does the direction of the electric field produced by that charge change?

Accepted Answer

It reverses direction

Question 18

Which of the following statements about the electric field from a dipole is correct?

Accepted Answer

The field decreases as $1/r^3$ with distance from the dipole

Question 19

A neutral atom is placed in a strong external electric field. What happens to the atom?

Accepted Answer

It becomes polarized, forming an induced dipole

Question 20

Which of the following best explains why the region between $-Q$ and $+4Q$ is ruled out for the electric field to be zero?

Accepted Answer

The electric fields from both charges point in the same direction in that region

Electric Fields: Point Charges, Dipoles, and Field Lines

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