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MCAT > concept 4c > Flashcards

concept 4c Flashcards

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1
Q

fundamental unit of charge

A

1.60e-19 C
a proton and an electron have the same amount of charge
proton is positively charged (+1.60e-19)
electron is negatively charged (-1.60e-19)

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2
Q

insulator

A

material that resits the movement of charge bc the electrons are tightly associated with their nuclei
not easily distribute a charge over its surface
will not transfer that charge to another neutral object very well

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3
Q

conductor

A

material that allows the free movement of electrical charge
one with very low or zero resistance
charges distributed evenly upon surface of the conductor
able to transfer and transport charges
often used in circuit or electrochemical cells

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4
Q

Coulomb’s law

A

relates the electrostatic force between 2 charged particles to their charges and the distance b/w them
quantifies he magnitude of electrostatic force (Fe)
Fe=kq1q2/r^2

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5
Q

Coulomb’s constant

A

aka electrostatic constant
k
number that depends on the units used in the equation
8.99e9 Nm^2/C^2

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6
Q

permittivity of free space

A

E(sub0)

8.85e-12 C^2/Nm^2

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7
Q

Electric Field

A

electric charge have surround electric field
exerts force on other charges that move into the space of the field
this force can be attractive or repulsive depending on the source charge and the test charge
E=Fe/q=kQ/r^2

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8
Q

source charge (Q)

A

produces and an electric field

if same as test charge the force is repulsive, if opposite of test charge the force is attractive

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9
Q

test charge (q)

A

charge that is placed in the electric field
when in electric field it will experience an electrostatic force (Fe) that is equal to qE (chargeXmag. of electric field)

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10
Q

field lines

A 
imaginary lines that represent how a positive test charge would move in the presence of the source charge 
they point away from positive charges 
point toward (in) negative charges
point from all surfaces of charge (form shape similar to bike wheel)
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11
Q

types of potential energy

A

gravitational
elastic
chemical
electrical

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12
Q

electrical potential energy (U)

A

depends on relative position of one charge w/ respect to another charge or collection of charges
U=kQq/r
if like charges U will be positive
if unlike charges U will be negative
is the work necessary to move a test charge from infinity to a point in space in an electric field surround a source charge

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13
Q

changing electrical potential energy

A

will increase when 2 like charges move toward each other or when 2 opposite charges move apart
will decrease when 2 like charges move apart or when 2 opposite charges move toward each other

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14
Q

electrical potential (V)

A

measure of electrical potential energy per unit charge
given in volts (V)
V=U/q=kQ/r

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15
Q

potential difference

A

difference of electrical potential b/w 2 distinct points
measured in volts
aka voltage
differences in electrical potential also drive current as electromotive force in a circuit
=Vb-Va=Wab/q (Wab is work needed to move test charge thought electric field from point a to b )

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16
Q

equipotential line

A

line on which the potential at every point is the same, thus the potential difference is 0
in 3D space they look like spheres surround the source charge

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17
Q

electric dipole

A

separation of equal and opposite charge by a small distance

can be seen in polar molecules

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18
Q

dipole moment (p)

A

p=qd

q is the charge and d is the separation distance

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19
Q

potential bisector of the dipole

A

equipotential in that lies halfway b/w +q and -q
has electric potential of 0 at any point along this plane
mag of he electric field is E=1/4piE(sub0)Xp/r^3

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20
Q

magnetic field

A 
any moving charge create a magnetic field 
can be a single electron traveling though space or a current through a conductive material 
unit tesla (T) 
for small magnetic fields measured in gauss 1T=10^4 gauss
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21
Q

classifying material

A

diamagnetic
paramagnetic
ferromagnetic

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22
Q

diamagnetic material

A

made of atoms with no unpaired electrons
have no net magnetic field
materials slightly repelled by a magnet so are weakly antimagnetic
common material you wouldn’t expect to stick to magnets: wood, plastic, water, glass, skin, etc.

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23
Q

paramagnetic materials

A

atoms with unpaired electrons
have net magnetic dipole but no net magnetic field
weakly magnetized in presence of external magnetic field
aligning magnetic dipoles with the external field
aluminum, copper, gold

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24
Q

ferromagnetic materials

A

have unpaired electrons
permanent atomic magnetic dipoles, oriented randomly so no net magnetic dipole
become strongly magnetized when exposed to magnetic field or under certain temps
iron, nickel, cobalt
bar magnets

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25
Q

magnetic field for long straight wire

A

B=u0I/2(pi)r

u0=mu not. permeability of free space= 4piX10^-7 Tm/A

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26
Q

magnetic field for circular loop

A

B=u0I/2r

pi is not included

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27
Q

right-hand rule for magnetic field

A

point thumb in direction of the current
wrap fingers around the current-carrying wire
fingers mimic the circular field lines, curling around the wire

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28
Q

Lorentz force

A

the sum of the electrostatic and magnetic forces acting on charges

29
Q

magnetic force

A

force exerted on a charge that moves in a magnetic field
Fb=qvBsin(theta)
q is charge, v is velocity, B mag of magnetic field, theta is b/w v and B (sin 0 and 180 equals zero)

30
Q

right-hand rule for magnetic force

A

to determine direction fo magnetic force:
position right thumb in direction of velocity
put fingers in direction of magnetic field lines
curl fingers toward direction of force

31
Q

Fb on a current-carrying wire

A

Fb=ILBsin(theta)

same right hand rule for magnetic field

32
Q

current

A 
the flow of positive charge 
but negative charges are actually moving 
I=Q/delta t 
unit ampere (1 A=1C/s) 
direction of current is opposite direction of electron flow
33
Q

conductivity

A

2 types: metallic and electrolytic

34
Q

metallic conductivity

A

conductivity in solid metals and the molten form of some salts
can easily lose one or more of their out electrons, then free to move around in larger collection of metal atoms
most metals are good electrical and thermal conductors

35
Q

electrolytic conductivity

A

conductivity in solutions
depends on the strength of a solution
sea water and orange juice are better conductors than di water

36
Q

metallic bond

A

sea of electrons flowing over and past a rigid lattice of metal cations
more accurately described as an equal distribution of charge density of free electrons across all of neural atoms within metallic mass

37
Q

direct current (DC)

A

charge flows in one direction only

current in household batteries

38
Q

alternating current (AC)

A

flow changes direction periodically

current supplied over long distances to homes and buildings

39
Q

galvanic (voltaic) cell

A

can produce a potential difference
spontaneous oxidation-reduction rxns that generate emf as a result of potential difference
standard batteries

40
Q

electromotive force (emf)

A

voltage when no charge is moving b/w the 2 terminals of a cell that are at different potential values
not actually a force but a potential difference
“pressure to move” that results in current

41
Q

Kirchhoff’s laws

A

2 rules that deal with the conservation of charge and energy within a circuit
junction rule and loop rule

42
Q

junction rule

A

current into junction=current leaving junction

43
Q

loop rule

A

Vsource=Vdrop

draw loop and add/subtract parts and set equal to zero

44
Q

resistance

A

opposition within any material to the moment and flow of charge
materials w/ no resistance are conductors
materials w/ high resistance are insulators

45
Q

resistors

A

conductive materials that offer amounts of resistance between conductors (no resistance) and insulators (high resistance)

46
Q

properties of resistors

A

resistance is dependents on characteristics of the resistor: resistivity, length, cross-sectional area, and temp.
R=pL/A
p is resistivity, L is length, A is area

47
Q

resistivity

A

measure of intrinsic resistance of a material independent of its shape or size
generally increases with temp
depends on the material of the resistor

48
Q

length

A

longer resistor greater resistance (bc electron has to travel a greater distance thought resistant material)

49
Q

cross-sectional area

A

inversely proportional to resistance
if area is doubled, resistance is halved
the wider the resistor the more current can flow, decreasing resistance

50
Q

conduction pathways

A

number of pathways through the resistor

increasing the area increases the conduction pathways

51
Q

temperature

A

most conductors have greater resistance at higher temperatures
due to increase thermal oscillation of atoms, producing greater resistance to electron flow

52
Q

Ohm’s Law

A

relates voltage, current, and resistance for a given circuit element
V=IR–> I=V/R and R=V/I
basic law of electricity

53
Q

power

A

rate at which energy is transferred or transformed

P=W/t=delta E/t

54
Q

power of resistor

A

rate at which energy is dissipated by a resistor

P=IV=I^2R=V^2/R

55
Q

resistors in series

A 
current flows thought each resistor 
there is a voltage drop w/ each resistor 
voltage drop--> 1/V=1/V1+1/V2+...
resistance--> R=R1+R2+... 
R increases as resistors are added
56
Q

resistors in parallel

A

allow charge to follow different parallel paths b/w high-potential terminal and low-potential terminal
V=V1+V2+…
1/R=1/R1+1/R2+…

57
Q

capacitors

A

characterized by their ability to hold charge at a particular voltage
2 electrically neutral metal pates connected to a voltage source

58
Q

capacitance

A 
ratio of magnitude of the charge stored on one place to the potential difference (voltage) across the capacitor 
C=Q/V 
unit farad (1F=1C/V)
59
Q

capacitance of parallel plate capacitor

A

dependent upon the geometry of the 2 conduction surfaces
C=E0(A/d)
E0=8.85e-12
there is a uniform electric field b/w the 2 plates E=V/d

60
Q

potential energy stored in a capacity

A

U=1/2CV^2

61
Q

dielectric material

A

insulation (insulating material)
used to increase capacitance
air, glass, plastic, ceramic, certain metal oxides

62
Q

dielectric constant (kappa)

A

how much the material increase the capacitance by

measure of materials insulating ability

63
Q

capacitance due to dielectric material

A

C(sub d)=(kappa)C

dielectric constant X capacitance w/o material

64
Q

capacitors in series

A

total capacitance decreases, and decreases as more capacitors are added
1/C=1/C1+1/C2+…

65
Q

capacitors in parallel

A

total capacitance equal to the same of individual capacitance
C=C1+C2+…

66
Q

meters

A

the devices that are used to measure circuit quantities in the read world

67
Q

ammeters

A

used to measure the current at some point within a circuit
inserted in series
high current will overwhelm the ammeter, low resistance shunt is used in parallel to allow reading

68
Q

voltmeter

A

requires a circuit to be active
use magnetic properties of current-carrying wires
used to measure the voltage drop across 2 points in a circuit
wired in parallel

69
Q

ohmmeter

A

does not require a circuit to be active

often have their own batter of known voltage and function as ammeters

MCAT (18 decks)

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