OAT: Electrostatics

What is the fundamental unit of charge (e) in C?

1.6x10⁻¹⁹

Example: A positive charge is attracted to a negative charge a certain distance away. The charges are then moved so that they are separated by twice the distance. How has the force of attraction changed between them? (Hint: doubling the distance quadruples the square of the distance)

1/4

What is the value of Coulomb's constant (k), or the electrostatic constant, in Nm²C⁻²?

9x10⁹

Which of the following is a unit of energy? A. eV B. Vm C. V/m D. W E. N

A

Example: A metal sphere, R, has a charge of -q coulombs. An identical metal sphere, S, has a charge of +2q coulombs. The magnitude of the electrical force on S due to R is F newtons. If an electron were placed midway between R and S, the resultant electric force on the electron would be: A. toward R B. toward S C. up D. down E. zero

B

Example: A metal sphere, R, has a charge of -q coulombs. An identical metal sphere, S, has a charge of +2q coulombs. The magnitude of the electrical force on S due to R is F newtons. The magnitude of the electric force on R due to S is: A. F/2 B. F C. 2F D. 3F E. 4F

B

Example: A positive charge of +Q is fixed at point R a distance of d away from another positive charge of +2Q fixed at point S. Point A is located midway between the charges, and point B is a distance of d/2 from the +2Q charge. Is the total electric field stronger at A or B?

B

Given an electric dipole, the electric potential is zero: A. only at the midpoint of the dipole axis B. anywhere on any perpendicular bisector of the dipole axis and at infinity C. anywhere on the dipole axis D. only for points at infinity E. only when a second dipole is introduced to the system

B

Example: A metal sphere, R, has a charge of -q coulombs. An identical metal sphere, S, has a charge of +2q coulombs. The magnitude of the electrical force on S due to R is F newtons. If the distance between the centers of the spheres is halved, the magnitude of the force on S due to R will be: A. F/4 B. F/2 C. 2F D. 3F E. 4F

E

For a collection of charges, the total electric field at a point in space is the vector sum of the electric field due to each charge, represented by what equation?

E=E(q1)+E(q2)+...

What are the two formulas for electric field (E)?

E=F/q₀=kq/r²

What is the formula for the electric field produced by an electric dipole, involving dipole moment, Coulomb's constant, and the distance from the midpoint of the two charges?

E=kp/r³

What is the formula for electrostatic force (F), which represents Coulomb's law and includes Coulomb's constant, two charges, and the distance between their centers?

F=k(q1q2/r²)

What is the formula for force (F) exerted on a charge?

F=qE

What is the formula for magnetic force (F) exerted on a moving charge, including the angle between vectors (θ), charge of the moving particle (q), particle's speed (v), and magnetic field (B)?

F=qvBsinθ

1 volt = 1 what?

J/C

What are the two formulas for electric potential energy (U) involving electric potential, multiple charges (q, Q), and distance between charges?

U=qV=kqQ/r

For a collection of charges, the total electric potential at a point in space is the scalar sum of the electric potential due to each charge, represented by what equation?

V=V(q1)+V(q2)+...

What are the two formulas for electric potential (V)?

V=W/q₀=kq/r

What is the equation for potential difference (voltage)?

Vb-Va=Wab/q₀

In what direction does the electrostatic force vector point?

along the line connecting the centers of two charges

Do unlike charges attract or repel?

attract

What is the SI unit of charge?

coulomb

Two equal and opposite charges a small distance away from each other form a what?

electric dipole

Every electric charge sets up a surrounding what, which can be detected by the force it exerts on other electric charges? **defined as the force a charge exerts on another stationary positive test charge (q₀) divided by the test charge

electric field

amount of work needed to move a positive test charge (q₀) from infinity to a certain point, divided by the quantity of charge q₀

electric potential

amount of work needed to move a test charge (q₀) from infinity to that point through an electric field created by a separate source charge

electric potential energy

Which is stronger: electrostatic or gravitational attraction between electrons and protons?

electrostatic

the force that exists between stationary charges

electrostatic force

line for which the potential at every point is the same; in other words, the potential difference between any two points is zero; no work is done when moving a test charge (q₀) from one point to another

equipotential line

imaginary lines that represent how a positive test charge would be accelerated in the electric field; also called lines of force For example, these for a negatively charged source particle would point radially toward the charge because the positive test charge would be attracted toward a negative charge. Similarly, these point radially away from a positive source charge because the positive test charge would be repelled away from another positive charge.

field lines

Moving charges create what?

magnetic fields

Example: A positive charge of 1x10⁻⁵ C is located one meter away from another positive charge of 2x10⁻⁵ C. How would you find at what point along the line between the two charges the electric field is equal to zero?

must have equal magnitudes and opposite directions, so set the equation up as k(1x10⁻⁵/x²)=k(2x10⁻⁵/(1-x)²), then simplify to 1/x²=2/(1-x)² and solve

If one charge is positive and one is negative, will electric potential energy be positive/negative and increase/decrease as the distance between them decreases?

negative, decrease

When an electric dipole is placed in a uniform external electric field, what is the net force? What is the net torque? What effect do these have on the dipole?

net force is zero but a nonzero torque causes dipole to rotate so dipole moment aligns with electric field

Does an electric field point in the same or opposite direction in regards to dipole moment?

opposite

In an electric dipole with two charges (-q and +q) a small distance (d) away from each other, what is the formula for dipole moment (p)?

p=qd

If both charges are positive or both are negative, will electric potential energy be positive/negative and increase/decrease as the distance between them decreases?

positive, increase

difference in potential between two points, same as the term "voltage" used in circuits Example: If a test charge q₀ is moved from point A with an electric potential Va to point B with an electric potential Vb, then this would be Vb-Va

potential difference

With equipotential lines, work does NOT depend on the path to move a test charge through an electric field between two points (therefore electrostatic force is conservative), but instead solely on what? (Hint: paths I, II, and III as shown in the image all require the same amount of work to move the electron)

potential difference of lines

What variable represents a charged particle?

q

The direction of the electric field vector (E) is determined by the sign of the source charge. For example, the electric field of a negative charge points in what direction?

radially inward toward charge

The direction of the electric field vector (E) is determined by the sign of the source charge. For example, the electric field of a positive charge points in what direction?

radially outward from charge

Macroscopic objects are usually electrically neutral, but they can become charged, for example, how?

removal of surface charges by friction

Do like charges attract or repel?

repel

In what direction does the electric field vector point?

same direction as F

Field lines can indicate the relative strength of an electric field. For example, where the field lines are closer together, the electric field is what?

stronger

Example: A positive charge of +Q is fixed at point R a distance of d away from another positive charge of +2Q fixed at point S. Point A is located midway between the charges, and point B is a distance of d/2 from the +2Q charge. In which direction will a positive charge move if placed at point A?

toward +Q

True or false: Protons and electrons have the same amount of charge (e), even though protons are positive (+e) and electrons are negative (-e).

true

Example: How would you find the potential energy of a system if a charge of +2e and a charge of -3e are separated by a distance of 3 nm? (e=1.6x10⁻¹⁹ C)

use the equation U=kqQr and plug in known values to get (8.99x10⁹)(2)(1.6x10⁻¹⁹)(-3)(1.6x10⁻¹⁹)/3x10⁻⁹

What is the SI unit of electric potential?

volts

Field lines can indicate the relative strength of an electric field. For example, where the field lines are farther apart, the electric field is what?

weaker

law stating that like charges repel and opposite charges attract, with a force proportional to the product of the charges and inversely proportional to the square of the distance between them

Coulomb's law

What are the SI units of dipole moment?

Cm

What are the SI units for electric field?

N/C