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Physics and Math Correct Deck > Ch. 5: Electrostatics and Magnetism > Flashcards

Ch. 5: Electrostatics and Magnetism Flashcards

1
Q

defn: electrostatics

A

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

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1
Q

what are the two types of charged subatomic particles?

A
  1. proton
  2. electron
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2
Q

defn: proton vs. electron

A

proton: positive charge
electron: negative charge

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3
Q

defn: attractive vs. repulsive forces

A

attractive forces: opposite charges

repulsive forces: like charges

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4
Q

is the electrostatic force attractive or repulsive?

A

can be either depending on the signs of the charges that are interacting

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5
Q

defn: ground

A

a means of returning charge to the earth

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6
Q

aka: static electricity

A

static charge buildup

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7
Q

SI unit: charge

A

coloumb

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8
Q

the proton and the electron share the same magnitude of charge, do they share the same mass?

A

no, the proton has a much greater mass than the electron

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9
Q

defn: insulator

+ explain on a molecular level

A

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

molecularly: the electrons of insulators tend to be closely linked with their respective nuclei

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10
Q

defn: conductor

+ explain on a molecular level

A

when given a charge, the charges will distribute approximately evenly upon the surface of the conductor

are able to transfer and transport charges

molecularly: conceptualized as nuclei surrounded by a sea of free electrons that are able to move rapidly throughout the material and are only loosely associated with the positive charges

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11
Q

what types of materials are generally conductors? what types are generally insulators?

A

insulators: nonmetals

conductor: metals, ionic (electrolyte) solutions

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12
Q

defn: Coulomb’s law

A

quantifies the magnitude of the electrostatic force between two charges

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13
Q

how do you determine the direction of the electrostatic force?

A

remember that unlike charges attract and like charges repel

the force always points along the line connecting the centers of the two charges

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14
Q

where do electric fields come from and how do they make their presence known?

A
  1. every electric charge sets up a surrounding electric field, just like every mass creates a gravitational field
  2. electric fields make their presence known by exerting forces on other charges that move into the space of the field
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15
Q

how is it determined if the force exerted through the electric field is attractive or repulsive?

A

it depends on whether the stationary TEST charge q and the stationary SOURCE charge Q are opposite or like charges

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16
Q

defn: test charge q vs. source charge Q

A

test charge = the charge placed in the electric field

source charge = the charge which actually creates the electric field

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17
Q

is the electric field a vector or scalar quantity?

A

vector

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18
Q

what are the two methods for calculating the magnitude of the electric field at a particular point in space?

A
  1. place a test charge q at some point within the 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
  2. we need to know the magnitude of the source charge and the distance between the source charge and point in space at which we want to measure the electric field
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19
Q

what is one disadvantage to the first method of calculating the magnitude of the electric field?

A

a test charge must actually be present in order for a force to be generated and measured

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20
Q

what is the direction of an electric field vector by convention?

A

the direction that a positive test charge would move in the presence of the source charge

(if the source charge is positive –> test charge experiences repulsive force, accelerate away from source charge)

(if the source charge is negative –> test charge experiences attractive force, accelerate toward the source charge)

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21
Q

based on the convention of electric field direction, what is the direction of electric field vectors for positive and negative charges?

A

positive charges have electric field vectors that radiate outward (point away) from the charge

negative charges have electric field vectors that radiate inward (point toward) the charge

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22
Q

defn + char: field lines

A

imaginary lines that represent how a positive test charge would move in the presence of the source charge

they are drawn in the direction of the actual electric field vectors and indicate the relative strength of the electric field at a given point in the space of the field

where the lines are closer together, the field is stronger, where they are farther apart the field is weaker

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23
Q

what is the net electric field equal to at a point in space for a collection of charges?

A

equal to the vector sum of all the electric fields

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24
Q

what is the direction of the electrostatic force when the test charge is positive? negative?

A

test charge within a field is positive: the force will be in the same direction as the electric field vector of the source charge

test charge within a field is negative: the force will be in the direction opposite to the field vector of the source charge

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25
Q

defn: electric potential energy

A

a 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

26
Q

what will the sign of electric potential energy be if the charges are like? unlike?

A

like charges: potential energy positive

unlike charges: potential energy negative

27
Q

defn: electric potential energy for a charge at a point in space in an electric field (in terms of work)

A

the amount of work necessary to bring the charge from infinitely far away to that point

28
Q

will the electric potential energy of a system increase or decrease when two like charges move towards each other or apart? when two opposite charges move towards each other or apart?

A

LIKE TOWARD: increase EPE

LIKE AWAY: decrease EPE

UNLIKE TOWARD: decrease EPE

UNLIKE AWAY: increase EPE

29
Q

defn + unit + scalar or vector: electric potential

A

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

unit: volts (V)

scalar

30
Q

how is the sign of electric potential determined?

A

by the source charge Q

if positive source: V positive

if negative source: V negative

31
Q

what is the electric potential at a point in spacefor a collection of charges?

A

the scalar sum of the electric potential due to each charge

32
Q

defn + aka: voltage

A

aka: potential difference

there is a potential difference between two points that are at different distances from the source charge because electric potential is inversely proportional to the distance from the source charge

33
Q

is electrostatic force conservative or nonconservative?

A

conservative!

34
Q

if allowed, charges will move spontaneously in whatever direction results in a decrease in electric potential energy, what does this mean for a positive and negative test charge in terms of electric potential, voltage, and work?

A

positive test charge
- move from higher electric potential to lower
- voltage is negative
- work is negative

negative test charge
- move from lower electric potential to higher
- voltage is positive
- work is negative

overall this means: positive charges move in direction that decreases their electric potential, negative charges spontaneously move in the direction that increases their electric potential but in BOTH cases, the electric potential energy is decreasing

35
Q

defn: equipotential line

A

a line on which the potential at every point is the same (the potential difference between any two points on an equipotential line is zero)

36
Q

what do equipotential lines look like on paper? in 3-D?

A

on paper: concentric circles surrounding a source charge

3-D: spheres surrounding the source charge

37
Q

is work done when moving a test charge from one point on an equipotential line to another point on the same line? between different lines?

A

same line, different point: no work

different lines: work done

38
Q

what does the work done in moving a test charge from one equipotential line to another depend on?

A

the potential difference of the two lines NOT on the pathway taken between them

39
Q

what does an electric dipole result from?

A

from two equal and opposite charges being separated a small distance d from each other

40
Q

example: transient electric dipole, permanent electric dipole

A

TRANSIENT: moment-to-moment changes in electron distribution that create London dispersion forces

PERMANENT: the molecular dipole of water or the carbonyl functional group

41
Q

what is a way of visualizing the electric dipole?

A

as a barbell

the equal weights on either end of the bar represent the equal and opposite charges separated by a small distance (the length of the bar)

42
Q

defn + SI unit + direction: dipole moment (p)

A

the product of charge and separation distance

SI unit: coloumb meter

direction: (physics): along the line connecting the charges (the dipole axis) with the vector pointing from negative to positive

(chemistry): points from positive towards negative usually

43
Q

defn: perpendicular bisector of the dipole

direction of electric field vectors?

A

a very important equipotential line –> the plane that lies halfway between +q and -q

electric field vectors point in the direction opposite to p

44
Q

why is the electric potential at any point along the perpendicular bisector of the dipole 0?

A

because the angle between this plane and the dipole axis is 90 deg (and cos 90 = 0)

45
Q

explain how torques can act on dipoles (3)

A
  1. when the electric dipole is placed in a uniform external electric field, each of the equal and opposite charges of the dipole will experience a force exerted on it by the field
  2. the forces acting on the charges will be equal in magnitude and opposite in direction, resulting in a situation of translational equilibrium
  3. there will be a net torque about the center of the dipole axis
46
Q

what effect does torque have on the dipole?

A

causes the dipole to reorient itself so that its dipole moment, p, aligns with the electric field, E

47
Q

how are magnetic fields created?

A

by any moving charge

48
Q

what is the SI unit for magnetic fields?

A

tesla (T)

49
Q

what are the 3 ways magnetic fields can be set up?

A
  1. movement of individual charges
  2. mass movement of charge in the form a current through a conductive material
  3. permanent magnets
50
Q

what is a gauss? why do we use it?

A

a unit for magnetic fields

used because Teslas are quite large

51
Q

defn + char (2) + ex (5): diamagnetic materials

A

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

char: slightly repelled by a magnet, can be called weakly antimagnetic

ex: common materials you wouldnt expect to get stuck to a magnet (wood, plastics, water, glass, skin)

52
Q

defn + char (3) + ex (3): paramagnetic materials

A

made of atoms that have unpaired electrons and thus have a net magnetic dipole moment

char: atoms are usually randomly oriented so that the material creates no net magnetic field, become weakly magnetized in the presence of an external magnetic field (aligning the magnetic dipoles of the material with the external field)

ex: aluminum, copper, gold

53
Q

what happens to paramagnetic materials upon removal of an external magnetic field?

A

the thermal energy of the individual atoms will cause the individual magnetic dipoles to reorient randomly

54
Q

defn + char + ex: ferromagnetic materials

A

made of atoms that have unpaired electrons and permanent atomic magnetic dipoles that are normally oriented randomly so that the material has no net magnetic dipole

char: become strongly magnetized when exposed to a magnetic field or under certain temps

ex: bar magnet

55
Q

what does the configuration of the magnetic field lines surrounding a current-carrying wire depend on?

A

the shape of the wire

56
Q

what is the shape of magnetic fields for straight wires? how do you determine the direction of the field vectors?

A

concentric rings

right-hand-rule (point your thumb in the direction of the current and wrap your fingers around the current-carrying wire) –> your fingers mimc the circular field lines (curling around the wire)

57
Q

what is the difference in the equations for the magnitude of a magnetic field curling around a straight wire vs. at the center of a circular loop wire that is determined by the difference in the “r”?

A

straight wire: gives the magnitude of the magnetic field at any perpendicular distance r from the current-carrying wire

circular loop: gives the magnitude of the magnetic field only at the center of the circular loop of current-carrying wire with radius r

58
Q

what can we assume in our discussion of the magnetic force on moving charges and on current-carrying wires and why?

A

WHAT: the presence of a fixed and uniform external magnetic field

WHY: magnetic fields exert forces only on other moving charges, they do not “sense” their own fields

59
Q

defn: Lorentz force

A

the sum of the electrostatic and magnetic forces acting on charges at the same time

60
Q

the magnetic force is a function of the sine of the angle, what does that imply about the charge in order for it to experience a magnetic force?

A

the charge must have a perpendicular component of velocity in order to experience a magnetic force

61
Q

if the charge is moving parallel or antiparallel to the magnetic field vector, will the charge experience a magnetic force?

A

no!

62
Q

what are the two right-hand rules in magnetism? (3 and 4 steps)

A

direction of magnetic field from current carrying-wire:
1. point your thumb in the direction of the current
2. wrap your fingers around the current-carrying wire)
3. your fingers mimic the circular field lines (curling around the wire)

direction of magnetic force on a moving charge:
1. position your right thumb in the direction of the velocity vector
2. put your fingers in the direction of the magnetic field lines
3. your palm will point in the direction of the force vector for a positive charge
4. the back of your hand will point in the direction of the force vector for a negative charge

Physics and Math Correct Deck (12 decks)

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