Chapter 5 Electrostatics and Magnetism

Question 1

Electrostatics Definition

Answer 1

The study of stationary charges and the forces that are created by and which act upon these charges

Question 2

Ground definition

Answer 2

• A means of returning charge to the earth

- Ex: doorknob

Question 3

Static Charge Buildup/Static Electricity-More significant in what environment

Answer 3

-More significant in drier air because lower humidity makes it easier for charge to become and remain sparated

Question 4

SI unit of Charge- Coulomb Value

Answer 4

e=1.60 x 10^-19 C

• protons and electrons both have this amount of charge (while proton +e and electron -e)
• same magnitude of charge, but not the same mass. Proton much greater mass than electron

Question 5

Insulator

Answer 5

-Will not easily distribute a charge over its surface and will not transfer that charge to another neutral object very well

Question 6

Conductor

Answer 6

• When a conductor is a given charge, the charges will distribute approx. evenly upon the surface of the conductor
• Generally metals, but ionic (electrolyte) solutions are also effective conductors

Question 7

Coulomb’s Law Equation

Answer 7

• Quantifies the magnitude of the electrostatic force Fe between two charges
• Fe=kq1q2/r^2
• Fe=magnitude of the electrostatic force
• k=Coulomb’s constant
• q1&q2=the magnitudes of the two charges
• r=distance between the charges

Question 8

Coulomb’s Constant

Answer 8

• Dependent on the units used in the equation

- SI units k=1/4piEo=8.99x10^9 n*m^2/C^2 where Eo(sigma naught) represents the permittivity of free space

Question 9

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?

Answer 9

(Based on Coulomb’s Law) The force between two charges varies as the inverse of the square of the distance between them. So if the distance is double, the square of the distance is quadrupled, so the force is reduced to one-fourth of what is was originally.

Question 10

Magnitude of an electric field equation

Answer 10

E=fe/q=kQ/r^2

• Fe= magnitude of the force felt by the test charge q
• k=electrostatic constant
• Q=the source charge magnitude
• r=distance of the two charges

Question 11

Fe/q use:

Answer 11

• place test charge q at some point in electric field, measure the force exerted on that test charge, and define the electric field at that point in space as the ratio of the force magnitude to test charge magnitude
• *** test charge must actually be present in order for a force to be generated and measured

Question 12

kQ/r^2

Answer 12

• Does not require the presence of a test charge
• Only need to know the magnitude of the source charge and the distance between the source charge and point in space where you want to measure the electric field
• Need to know the value of the source charge to be able to calculate the electric field

Question 13

Electrical Potential Energy

Answer 13

-Form of potential energy that is dependent on the relative position of one charge with respect to another charge or to a collection of charges

Question 14

Electrical Potential Energy Equation

Answer 14

U=kQq/r
-if the charges are like charges (both positive or both negative), the potential energy will be positive. If the charges are unlike (one positive and the other negative) the potential energy will be negative

Question 15

Electrical Potential

Answer 15

The ratio of the magnitude of a charge’s electrical potential energy to the magnitude of the charge itself

Question 16

Electrical Potential Equation

Answer 16

V=U/q

• V=electrical potential measured in volts (V) & 1V=1J/C
• If there is no test charge q, you can still calculate the electrical potential of a point in space in an electric field as long as you know the magnitude of the source charge and the distance from the source charge to the point in space in the field– V=kQ/r
• For a positive source charge, V is positive. For a negative source charge, V is negative

Question 17

Voltage

Answer 17

The potential difference between points Va and Vb

Vb-Va

Question 18

Change in Voltage

Answer 18

ΔV=Vb-Va=Wab/q

• Wab is the work needed to move a test charge q through an electric field from point a to point b
• Work is independent of the actual pathway taken and only depends on the potentials at the two points a and b

Question 19

Equipotential line

Answer 19

A line on which the potential at every point is the same

-potential difference between points = 0

Question 20

Electric dipole

Answer 20

• results from two equal & opposite charges being separated by a small distance d from eachother
• can be transient (like moment by moment changing distribution of elections in the electron cloud of an atom)
• can be permanent (like molecular dipole of water or the carbonyl functional group)

Question 21

Diamagnetic materials

Answer 21

-Made of atoms with no unpaired electrons and that have no net magnetic field

Question 22

Paramagnetic materials

Answer 22

• Become weakly magnetized in the presence of an external magnetic field, aligning the magnetic dipoles with the external field
• Upon removal of the external field, the thermal energy of the individual atoms will cause the individual magnetic dipoles to reorient randomly

Question 23

Ferromagnetic materials

Answer 23

• have unpaired electrons and permanent atomic magnetic dipoles that are normally oriented randomly so the material has no net magnetic dipole.
• Different from paramagnetic materials bcs ferromagnetic become strongly magnetized when exposed to a magnetic field or under certain temperatures
• Bar magnets are ferromagnetic materials with a north and south pole. Field lines exit the north pole and enter the south pole.

Question 24

Lorentz Force

Answer 24

The sum of electrostatic and magnetic forces acting on a charge at the same time