Question 1

Which of the following best describes the principle of superposition as it applies to electric forces?

Accepted Answer

The net electric force on a charge is the vector sum of all individual electric forces acting on it.

Question 2

A point charge $$+Q is $$placed at the origin. What is the direction of the electric field at a point located on the positive $$x-$$axis?

Accepted Answer

Away from the origin

Question 3

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

Accepted Answer

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

Question 4

If two point charges, $$+Q$$ and $$-Q$$, are separated by a distance $$d$$, what is the direction of the electric field at a point far along the axis passing through both charges (the dipole axis)?

Accepted Answer

From $$+Q to$$ $$-Q$$

Question 5

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

Accepted Answer

Electric field lines can form closed loops.

Question 6

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

Accepted Answer

$$\vec{F} = q\vec{E}$$

Question 7

Which of the following best describes an electric dipole?

Accepted Answer

Two charges of equal magnitude and opposite sign separated by a distance $$d$$

Question 8

What is the expression for the electric dipole moment $$\vec{p}$$ for two charges $$+q$$ and $$-q$$ separated by a vector $$\vec{d}$$?

Accepted Answer

$$\vec{p} = q\vec{d}$$

Question 9

For a point far from an electric dipole (distance $$y \gg d$$), what is the approximate magnitude of the electric field along the dipole axis?

Accepted Answer

$$E_y = \frac{qd}{2\pi\$$epsilon_0$$ y^3$}$$

Question 10

Which of the following is a correct statement about the number of electric field lines leaving or entering a charge?

Accepted Answer

It is proportional to the magnitude of the charge.

Question 11

A water molecule is shown with a positive and negative region. What physical property does this illustrate?

Accepted Answer

The molecule is an electric dipole.

Question 12

Which of the following best describes the direction of the electric field at a point near a negative point charge?

Accepted Answer

Radially inward toward the charge

Question 13

If three point charges are placed at the vertices of an equilateral triangle, what is the net electric force on one of the charges due to the other two?

Accepted Answer

The vector sum of the forces from each of the other two charges

Question 14

Which of the following is a correct mathematical definition of the electric field at a point?

Accepted Answer

$$\vec{E} = \frac{\vec{F}_E}{q}$$

Question 15

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

Accepted Answer

They cross each other at points of equal field strength.

Question 16

A small test charge is placed in the region between a positive and a negative charge of equal magnitude. What is the direction of the net electric field at the midpoint?

Accepted Answer

From the positive charge to the negative charge

Question 17

Which of the following best describes the electric field produced by a continuous distribution of charge?

Accepted Answer

It is the vector sum (integral) of the fields produced by each infinitesimal charge element.

Question 18

Which of the following is the correct expression for the electric field at a point $$(0, y)$$ along the axis of a dipole, for $$y \gg d$$?

Accepted Answer

$$E_y = \frac{qd}{2\pi\$$epsilon_0$$ y^3$}$$

Question 19

Which of the following is a correct application of the binomial approximation $$1 + x^n \approx 1 + nx$$ for $$x \ll 1$$?

Accepted Answer

It is used to simplify the expression for the electric field of a dipole at large distances.

Electric Fields and Dipoles: Principles and Calculations

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