Q: What is the torque $$\vec{\tau} on an $$electric dipole $$\vec{p} in a $$uniform external electric field $$\vec{E}$$?

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

Question 1

Which of the following statements about electric charge is correct?

Accepted Answer

Electric charge is quantized and always occurs in integer multiples of $$e = 1.60 	imes 10$$^{-19}$$\ \mathrm{C}.$$

Question 2

A glass rod is rubbed with silk, resulting in the rod becoming positively charged. What happens at the atomic level?

Accepted Answer

Electrons are transferred from the rod to the silk.

Question 3

Two point charges, $$q_1 = 2.0$$\ \mu\mathrm{C}$$ and q_2$ = -3.0\ \mu\mathrm{C}$$, are separated by $$0.50\ \mathrm{m}. $$What is the magnitude of the force between them? Use $$k = 8.99 	imes 10^9$\ \mathrm{N}\cdot\mathrm{m}^2/\mathrm{C}^2.$$

Accepted Answer

$$0.216\ \mathrm{N}$$

Question 4

Which of the following best describes the process of charging by induction?

Accepted Answer

Redistributing charges in an object due to the presence of a nearby charged object, without direct contact.

Question 5

Refer to the first image. Three point charges of equal magnitude are at the corners of an equilateral triangle. What is the direction of the net force on charge 2?

Accepted Answer

Up

Question 6

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

Accepted Answer

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

Question 7

A negative charge is placed in a region where the electric field is directed vertically upward. What is the direction of the electric force on this charge?

Accepted Answer

Down

Question 8

If two identical conducting spheres, one with $$+12.0\ \mathrm{nC}$$ and the other with $$-18.0\ \mathrm{nC}$$, are connected by a conducting wire and then separated, what is the final charge on each sphere?

Accepted Answer

$$-3.0\ \mathrm{nC}$$

Question 9

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

Accepted Answer

Field lines can cross each other.

Question 10

A uniformly charged insulating rod of length $$L is $$bent into a semicircle of radius $$R. $$What is the direction of the electric field at the center of the semicircle?

Accepted Answer

Along the symmetry axis perpendicular to the diameter of the semicircle

Question 11

What is the torque $$\vec{	au} on an $$electric dipole $$\vec{p} in a $$uniform external electric field $$\vec{E}$$?

Accepted Answer

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

Question 12

Which of the following is the correct formula for the electric field due to a continuous charge distribution?

Accepted Answer

$$E = \dfrac{1}{4\pi\$$epsilon_0$$} \int \dfrac{dq}{r^2$} \hat{r}$$

Question 13

A test charge $$q_0 is $$placed in an electric field $$\vec{E}. $$What is the force experienced by the test charge?

Accepted Answer

$$\vec{F}_e = q_0$ \vec{E}$$

Question 14

Which of the following best describes the concept of superposition in electrostatics?

Accepted Answer

The net electric force on a charge is the vector sum of the forces exerted by all other charges.

Question 15

If the distance between two point charges is doubled, what happens to the magnitude of the electric force between them?

Accepted Answer

It is reduced to one-fourth its original value.

Question 16

Which of the following is the correct expression for the potential energy $$U of an $$electric dipole in an external electric field $$\vec{E}$$?

Accepted Answer

$$U = -\vec{p} \cdot \vec{E}$$

Question 17

A charged object is brought near a neutral conductor. What happens to the charges in the conductor?

Accepted Answer

They redistribute, with opposite charges moving closer to the external charge.

Question 18

Which of the following is NOT a correct statement about conductors and insulators?

Accepted Answer

Insulators cannot be polarized.

Question 19

Refer to the sixth image. What is the direction of the dipole moment $$\vec{p}$$ for the dipole shown?

Accepted Answer

From $$-q to$$ $$+q$$

Question 20

A hydrogen atom consists of a single proton and a single electron. The electric force between them is about $$10^{40}$$ times stronger than the gravitational force. Is it possible to find a separation at which the two forces are equal?

Accepted Answer

No, it is not possible.

Electric Charge and Electric Field: Fundamental Concepts and Applications

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