Q: Which equation correctly gives the torque $$\tau on an $$electric dipole $$\vec{p} in a $$uniform external electric field $$\vec{E}$$?

$$\tau = \vec{p} \times \vec{E}$$

Question 1

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

Accepted Answer

Electric field lines never intersect and always point away from positive charges and toward negative charges.

Question 2

A dipole consists of charges $$+q$$ and $$-q$$ separated by a distance $$d. $$What is the direction of the electric dipole moment $$\vec{p}$$?

Accepted Answer

From the negative charge to the positive charge.

Question 3

Which of the following best describes the relationship between electric field vectors and electric field lines at a given point?

Accepted Answer

The electric field vector is tangent to the field line at that point.

Question 4

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

Accepted Answer

It develops an induced dipole moment aligned with the external field.

Question 5

Which equation correctly gives the torque $$	au on an $$electric dipole $$\vec{p} in a $$uniform external electric field $$\vec{E}$$?

Accepted Answer

$$	au = \vec{p} 	imes \vec{E}$$

Question 6

If the electric field at a point is represented by a high density of field lines, what does this indicate about the magnitude of the field at that point?

Accepted Answer

The field is strong at that point.

Question 7

Which of the following is the correct formula for the electric dipole moment $$\vec{p}$$ for two charges $$+q$$ and $$-q$$ separated by a distance $$d$$?

Accepted Answer

$$\vec{p} = qd$$

Question 8

A permanent electric dipole is placed in a uniform electric field. What is the net force and net torque on the dipole?

Accepted Answer

Net force is zero, net torque is nonzero.

Question 9

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

Accepted Answer

Field lines are vectors that indicate the magnitude and direction of the field.

Question 10

Given a point charge $$q at $$the origin, what is the direction of the electric field at a point on the $$x-$$axis at $$x \u003e 0$$?

Accepted Answer

Away from the origin if $$q is $$positive.

Question 11

Which of the following best describes the field lines for a system of two equal but opposite charges (an electric dipole)?

Accepted Answer

Field lines start on the positive charge and end on the negative charge, curving outward between them.

Question 12

The electric field at a point due to a dipole on its axial line (along the line joining the charges) at a distance $$r$$ from the center is given by:

Accepted Answer

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

Question 13

A student draws electric field lines for a single positive point charge. Which of the following errors would violate the rules for field lines?

Accepted Answer

Drawing field lines that cross each other.

Question 14

Which of the following is a correct statement about the superposition principle for electric fields?

Accepted Answer

The net electric field at a point is the sum of the electric fields due to each charge.

Question 15

A molecule with a permanent dipole is placed in a non-uniform electric field. What happens to the molecule?

Accepted Answer

It experiences a net force and a net torque.

Question 16

Which of the following best explains why field lines never cross?

Accepted Answer

Because the electric field at a point can have only one direction.

Question 17

A small test charge is placed at a point where the electric field is nonzero. What force does it experience?

Accepted Answer

A force in the direction tangent to the field line at that point.

Question 18

Which of the following is the correct expression for the electric field at a distance $$r$$ from a point charge $$q$$?

Accepted Answer

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

Question 19

In a field diagram, what does the length of the electric field vector at a point represent?

Accepted Answer

The magnitude of the electric field at that point.

Visualizing Electric Fields and Electric Dipoles (General Physics II, Chapter 5.5–5.6)

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