Physics I: 9-12 Flashcards
1
Q
opposite charges exert ___ forces
A
attractive
2
Q
like charges exert ___ forces
A
repulsive
3
Q
coulomb
A
fundamental unit of charge
4
Q
insulator
A
does not easily distribute a charge over its surface
will not transfer that charge to another neutral object very well
ex: nonmetals
5
Q
describe the electrons of insulators
A
tend to be closely linked with their respective nuclei
6
Q
conductor
A
- charges distribute evenly upon its surface
- able to transfer and transport charges
- often used in circuits or electrochemical cells
- ex: metals, ionic (electrolyte) solutions
7
Q
when placed one meter apart from each other, which will experience a greater acceleration: one coulomb of electrons or one coulomb of protons?
A
electrons will experience the greater acceleration because they are subject to the same force as the protons but have significantly smaller mass
8
Q
what is the net charge of an object with one coulomb of electrons and 3 moles of neutrons?
A
net charge is -1 C
neutrons do not contribute charge
9
Q
coulomb’s law quantifies…
A
the magnitude of the electrostatic force Fe
10
Q
coulomb’s law eq
A
k = coulomb’s/electrostatic constant
11
Q
permittivity of free space
A
ε0
12
Q
how to know direction of electric force in coulomb’s law
A
unlike charges attract, like charges repel
force always along the line connecting the centers of the 2 charges
13
Q
how is the magnitude of the electric force related to the square of the distance of separation?
A
inversely proportional
14
Q
electric fields
A
exerts forces on other charges
15
Q
electric fields are produced by
A
source charges (Q)
16
Q
when a test charge (q) is placed in an electric field (E), it will experience
A
an electrostatic force (Fe) equal to qe
17
Q
test charge
A
q
charge placed in the electric field
18
Q
source charge
A
Q
creates the electric field
19
Q
magnitude of electric field eq
E =
A
E = Fe/q = kQ / r2
divide coulomb’s law by q
20
Q
direction of electric field vector is given as…
A
the direction that a positive test charge would move in the presence of the source charge
21
Q
positive charges have electric field vectors that radiate…
A
outward (point away) from the charge
22
Q
negative charges have electric field vectors that radiate…
A
inward (point toward) the charge
23
Q
field lines
A
- imaginary lines that represent how a positive test charge would move in the presence of a source charge
- point away from positive charge
- point toward negative charge
24
Q
where will positive test charges move in regard to the field lines?
A
move in the direction of the field lines
25
where will negative test charges move in regard to the field lines?
move in the direction opposite of field lines
26
what is the electric field midway between two negative charges in isolation?
electric field would be zero because the two charges are the same
in this case, the fields exerted by each charge at the midpoint will cancel out and there will be no electric field
27
electric potential energy
potential energy that is dependent on the relative position of one charge with respect to another charge
28
electric potential energy eq
U = kQq/r
29
if charges are like charges, then the potential energy will be \_\_\_\_\_
positive
30
if charges are unlike charges, then the potential energy will be \_\_\_\_\_
negative
31
electric field is defined as the amount of work...
amount of work necessary to move a test charge from infinity to a point in space in an electric field surrounding a source charge
32
electric potential energy of a system increases when
two like charges move toward each other or when two opposite charges move apart
33
electric potential energy of a system decreases when
two like charges move apart or when two opposite charges move toward each other
34
how does a change in electric potential energy from -4 J to -7 J reflect on the stability of a system?
A decrease in potential energy indicates that the system has become more stable.
35
how does electric potential energy change between two particles as the distance between them increases?
if both particles have the same charge, the electric potential energy decreases as the distance increases.
if the particles have opposite charges, then the electrical potential energy increases as distance increases.
36
electric potential
V
ratio of the magnitude of a charge's electric potential energy to the magnitude of the charge itself
scalar
37
electric potential eq
V = U/q = kQ/r
38
how to determine electric potential sign
determined by source charge Q
39
how are electric potential and distance from the source charge related?
inversely proportional
40
positive charge moves from
+ to -
41
negative charges moves from
- to +
42
potential difference
voltage
change in electric potential that accompanies the movement of a test charge from one position to another
43
potential difference eq
ΔV = Vb - Va = Wab / q
Wab = work needed to move a test charge q through an electric field from point a to point b
44
positive charges will spontaneously move in the direction that \_\_inc/dec\_\_ their electric potential (\_\_pos/neg\_\_ voltage)
electric potential energy is \_\_inc/dec\_\_
decrease
negative
decreasing
45
negative charges will spontaneously move in the direction that \_\_inc/dec\_\_ their electric potential (\_\_pos/neg\_\_ voltage)
electric potential energy is \_\_inc/dec\_\_
increases
positive
decreasing
46
what is the difference between electric potential and voltage?
Electrical potential is the ratio of a charge's electrical potential energy to the magnitude of the charge itself.
Voltage, or potential difference, is a measure of the change in electrical potential between two points, which provides an indication of the tendency toward movement in one direction or the other.
47
how will a charge that is placed at a point of zero electric potential move relative to a source charge?
A charge will move in such a way to minimize its potential energy. Placing a charge at a point of zero electrical potential does not indicate that there is zero potential difference, so the charge may or may not move-and if it moves, it may move toward or away from the source charge depending on the sign of the source charge and test charge.
48
T/F
the units of electric potential energy and electric potential are different
true
electric potential energy - J
electric potential - V
49
equipotential line
line on which the potential at every point is the same
the potential difference between any two points on an equipotential line is zero
50
equipotential lines and work
* no work is done when moving a test charge from one point on an equipotential line to another
* work will be done in moving a test charge from one line to another
* but the work depends only on the potential difference of the two lines (not on the pathway taken between them)
51
electric dipole
two charges of opposite sign separated by a fixed distance
52
dipole moment eq
p = qd
53
perpendicular bisector of the dipole
electric potential at any point along this plane is 0
54
in an external electric field, an electric dipole will experience
net toque until it is aligned with the electric field vector
55
what is the voltage between two points on an equipotential line? will this voltage cause a charge to move along the line?
no voltage, so no acceleration along the line
there is a potential difference between different sets of equipotential lines, which can cause particles to move and accelerate
56
what is the behavior of an electric dipole when exposed to an external electric field?
a dipole will rotate within an external electric field such that its dipole moment aligns with the field
57
True or false? Because the increasing distance between charged particles repelling each other will decrease the Electrostatic Force, they will also slow down as they move.
False. Because the increasing distance between charged particles repelling each other will decrease the Electrostatic Force, they will also have a lower acceleration (but still increase their velocity traveling away from each other).
58
In \_\_\_\_\_\_\_\_\_\_\_\_\_\_, the positively charged nucleus cannot move around. In \_\_\_\_\_\_\_\_\_\_\_\_\_\_, the negatively charged electrons cannot move around.
(A) insulators, insulators
(B) insulators, insulators and conductors
(C) insulators and conductors, insulators and conductors
(D) insulators and conductors, insulators
(D) insulators and conductors, insulators
In insulators and conductors, the positively charged nucleus cannot move around. In insulators, the negatively charged electrons cannot move around.
59
Compare the process of Charge by Conduction to Charge by Induction.
In Charge by Conduction, you charge a neutral object by physically touching a negatively-charged object to it.
In Charge by Induction a charge is induced by bringing a negatively charged object close to another object.
60
A Dielectric is a substance that is normally not polarized, but in an electric field, a small charge can be induced. This acts to stabilize the source charge, and can allow more charges to be stored. Which of the following could be a dielectric?
(A) Insulator
(B) Conductor
(C) Neither Insulator nor Conductor
(D) Both Insulator and Conductor
(A) Insulator
An Insulator is a Dielectric that is normally not polarized, but in an electric field, a small charge can be induced. This acts to stabilize the source charge, and can allow more charges to be stored.
61
Draw out how induction might result in two neutrally-charged metal balls becoming oppositely charged.
62
A "Ground" is an infinite reservoir for electrons. What does that mean? Give an example.
A "Ground" is an infinite reservoir for electrons, which means that it can accept an infinite number of electrons. An example would be the earth.
63
What equation can be used to relate Electric Field Strength (E) to Electrostatic Force (Fe)
Fe / q = E
```
Fe = Electrostatic Force
q = Test Charge
E = Electric Field Strength
```
64
True or false? Even if there are no other charges to affect, a single charge (the source charge) will still create an electric field.
True. Even if there are no other charges to affect, a single charge (the source charge) will still create an electric field.
65
What equation can be used to relate E to the distance between two charges?
E = k (Q / r^2)
```
E = Electric Field Strength
Q = Source Charge
r = Distance between Q and q
```
66
True or False? A charge is repelled from another charge. As the two charges get farther away from one another, they will move slower and slower.
False. A charge is repelled from another charge. As the two charges get farther away from one another, they will accelerate at a slower and slower rate due to the decreasing Electrostatic Force. Remember that Force is not directly related to velocity but rather acceleration.
67
What is the difference between Electric Potential and Electric Potential Energy?
Electric Potential Energy is the amount of energy required to move a charge from one location to another (units = J).
Electric Potential is the amount of energy required to move a charge from one location to another per unit charge (units = J/C).
68
What equation can be used to relate Electrostatic Force to Electric Potential Energy?
Fe = EPE/r (similar to F = mgh)
```
Fe = Electrostatic Force
EPE = Electric Potential Energy
r = Radius between the two charges
```
69
What equation can be used to relate Electric Potential Energy to Electric Potential?
EPE / q = V
```
EPE = Electric Potential Energy
q = Charge
V = Electric Potential
```
70
What equation is used to relate Electric Potential (V) to the Source Charge (Q)?
V = k (Q / r)
```
V = Electric Potential
k = Coulomb's Constant (9⋅10^9)
Q = Source Charge
r = Radius between Q and q
```
71
A Test Charge (6.7⋅10^-14 C) is sitting 2.4⋅10^-3 meters away from a Source Charge. What is the Electrostatic Force (in N) between these two charges if the Voltage is equal to 4.3 V at that point?
(A) 9.87⋅10^-12
(B) 4.32⋅10^-15
(C) 2.88⋅10^-13
(D) 1.20⋅10^-10
(D) 1.20⋅10^-10
EPE / q = V
EPE / (6.7⋅10^-14) = 4.3
EPE = (6.7⋅10^-14) x (4.3)
EPE = approx. 3⋅10^-13 J (actual: 2.881⋅10^-13)
```
Fe = EPE / r
Fe = (3⋅10^-13) / (2.4⋅10^-3)
Fe = approx. 1⋅10^-10 N (actual: 1.20⋅10^-10)
```
72
A Test Charge (6.7⋅10^-14 C) is sitting 2.4⋅10^-3 meters away from a Source Charge (4.2⋅10^-12 C). What is the Electric Potential Energy (in J) between these two charges?
(A) 4.55⋅10^-9
(B) 6.87⋅10^-10
(C) 2.23⋅10^-11
(D) 1.05⋅10^-12
(D) 1.05⋅10^-12
```
V = k (Q / r)
V = (9⋅10^9) ((4.2⋅10^-12) / (2.4⋅10^-3))
V = (9⋅10^9) (approx. 2⋅10^-9 (actual: 1.75⋅10^-9))
V = approx. 18 (actual: 15.75)
```
EPE / q = V
EPE / 6.7⋅10^-14 = 18
EPE = 1⋅10^-12 J (actual: 1.05⋅10^-12)
73
Compare the Electrostatic Equations for F, E, EPE, and V.
74
b
75
76
b
77
a
78
b
79
b
80
a
81
b
82
a
83
magnetic field
created by any moving charge, whether a single electron traveling through space or a current through a conductive material
84
SI unit for magnetic field strength
tesla, T
85
1 T = ? gauss
104
86
diamagnetic
no unpaired electrons
no net magnetic field
slightly repelled by magnet (weakly antimagnetic)
87
paramagnetic
unpaired electrons
weakly magnetized in presence of external magnetic field
ex: aluminum, copper, gold
88
ferromagnetic
unpaired electrons
permanent atomic magnetic dipole
become strongly magnetized when exposed to a magnetic field or under certain temperatures
ex: iron, nickel, cobalt
89
magnitude of the magnetic field for an infinitely long and straight current-carrying wire
eq
B = µ0I / 2πr
B = magnetic field
I = current
r = distance from wire
90
what shape magnetic field do straight wires create?
concentric rings
91
magnitude of the magnetic field for a circular loop of current carrying wire
eq
B = µ0I / 2r
B = magnetic field
I = current
r = distance from wire
92
magnetic fields only exert forces on
other moving charges
93
lorentz force
sum of electrostatic and magnetic forces acting on a body
94
force on a moving charge eq
Fb = qvB sin theta
q = charge
v = velocity
B = magnitude of magnetic field
95
sin 0 =
0
96
sin 180 =
0
97
any charge moving parallel or antiparallel to the direction of the magnetic field will experience...
no force from the magnetic field
98
right hand rule for magnetic force
* thumb - velocity
* finger - field lines
* palm - force on a positive charge
99
magnetic force on a current carrying wire eq
Fb = ILB sin theta
I = current
L = length of wire
100
what are the requirements to have a nonzero electric field?
to create an electric field, one needs a charge
101
what are the requirements to have a nonzero magnetic field?
to create a magnetic field, one needs a moving charge
102
what are the requirements to have a nonzero magnetic force?
to create a magnetic force, one needs an external electric field acting on a charge moving any direction except parallel or antiparallel to the external field
103
Draw the magnetic field lines coming out of a simple bar magnet.
104
Which of the following is not one of the most common ferromagnetic materials?
(A) Zinc
(B) Iron
(C) Nickel
(D) Cobalt
(A) Zinc
The three most common ferromagnetic materials are Iron, Nickel and Cobalt.
105
A proton (q = 1.602⋅10^-19 C) is travelling through a magnetic field (B = .27 T) at an angle of 47° with a velocity of 4.5⋅10^7 m/s. What is the Magnetic Force acting on this proton?
(A) 1.42⋅10^-12
(B) 6.78⋅10^-13
(C) 9.22⋅10^-14
(D) 3.09⋅10^-15
(A) 1.42⋅10^-12
```
F = qvBsinθ
F = (1.602⋅10^-19) (4.5⋅10^7)(.27)sin47°
F = (1.602⋅10^-19) (4.5⋅10^7)(.27)(approx. √2/2 or .7 (actual: .731))
F = approx. 1.5⋅10^-12 (actual: 1.423⋅10^-12)
```
106
True or false? If the charged particle has no outside forces acting on it, then it will never create a magnetic field.
False. If the charge has no outside forces acting on it AND its initial velocity is 0, then it will never create a magnetic field.
Having no outside forces act on the charge just means it won't accelerate, not that it will have no velocity.
107
Your professor makes an analogy comparing centripetal force to magnetic force. How are these two concepts related?
When magnetic force acts on a charge, it causes it to change directions in a way that makes it go in a circle.
108
a
109
a
110
a
Fb = qvB sin theta
111
b
112
current
I
* movement of charge that occurs between two points that have different electrical potentials
* movement of positive charge from high potential end of voltage source to low potential end
* reality: electrons move from low potential to high potential
113
metallic conductivity
* relies on uniform movement of free electrons in metallic bonds
* metal atoms can easily lose one or more of their outer electrons -\> make them free to move around other metal atoms
114
electrolytic conductivity
relies on the ion concentration of a solution
depends on the strength of the solution
115
magnitude of current in terms of charge eq
I = Q/Δt
116
where do electrons move in a current
electrons move from lower electrical potential to higher electrical potential
117
potential difference (voltage) can be produced by...
electrical generator, galvanic (voltaic cell)
118
electromotive force
emf
voltage when no charge is moving between the two terminals of a cell that are at different potential values
119
kirchhoff's junction rule
at any point or junction in a circuit, the sum of th currents directed into that point equals the sum of currents directed away from that point
Iinto junction = Ileaving junction
120
kirchhoff's loop rule
around any closed circuit loop, the sum of voltage sources will always be equal to the sum of voltage (potential) drops
Vsource = Vdrop
121
provide the SI units of current
amperes (C/s)
122
voltage SI units
volts (J/C)
123
electromotive force SI units
volts (J/C)
124
conductivity SI units
siemens (S)
125
which likely has a higher conductivity: 1 M glucose or 0.25M NaCl? why?
NaCl because it is a salt and will increase the ion content of the water
glucose does not dissociate
126
resistance
R
the opposition within any material to the movement and flow of charge
127
materials that offer almost no resistance are called
conductors
128
materials that offer very high resistance are called
insulators
129
resistors
conductive materials that offer amounts of resistance
middle
130
resistance eq
R = ρL / A
ρ = resistivity
L = length of resistor
A = cross sectional area
131
resistivity
ρ
intrinsic resistance to current flow in a material
132
how is the resistance of a resistor related to its length?
directly/linearly proportional
133
how is the reissitance related to the cross sectional area of the resistor?
inversely proportional
134
the wider the resistor, the ___ current that can flow
more
135
how is temperature related to resistance?
proportionally
most conductors have greater resistance at higher temperature due to increased thermal oscillation
136
ohm's law
for a given resistance, the magnitude of the current through a resistor is proportional to the voltage drop across the resistor
V = IR
137
voltage drop between any two points in a circuit eq
V = IR
V = voltage drop
R = magnitude of resistance
138
what happens when a cell is discharging?
* it supplies current
* current flows from the positive, higher potential end of the cell, around the circuit to the negative, lower potential end
139
power eq in terms of work and time
P = W / t = ΔE / t
140
power of a resistor eq
P = IV = IR2 = V2/R
141
resistors in series
all current must pass sequentially through each resistor connected in a linear arrangement
142
resistors in parallel
current divides to pass through resistors separately
143
describe what happens to resistors in series
as the electrons flow through each resistor, energy is dissipated, and there is a voltage drop associated with each resistor
Rs increases as more resistors are added
144
Rs \_\_\_\_\_ as more resistors are added
increases
145
voltage and resistance eqs
resistors in series
Vs = V1 + V2 + V3 + ... + Vn
Rs = R1 + R2 + R3 + ... + Rn
146
147
Rp ___ as more resistors are added
decreases
148
describe what happens to resistors in parallel
voltage drop by each division of current is the same bc all pathways originate from a common point and end at a common point
current will be largest through the pathways with the lowest resistance
149
voltage and resistance eqs
resistors in parallel
Vp = V1 + V2 + V3 + ... + Vn
1/Rp = 1/R1 + 1/R2 + 1/R3 + ... + 1/Rn
150
when n identical resistors are wired in parallel, the total resistance =
R/n
151
for equal resistances, the current flowing through each of the resistors =
Itotal/n
152
when approaching circuit problems, you need to find:
total voltage, total resistance, total current
to find the total current, find the total resistance first
153
what four physical quantities determine the resistance of a resistor?
1. resistivity
2. length
3. cross sectional area
4. temperature
154
155
capacitors
have the ability to store and discharge electrical potential energy
156
capacitance
C
in parallel plate capacitors
determined by the area of the plates and the distance between the plates
157
capacitance eq
C = Q/V
158
magnitude of electric field eq
E = V/d
d = distance between the plates
159
potential energy stored in a capacitor eq
U = 1/2 CV2
160
dielectric material
insulators placed between the plates of a capacitor that increase capacitance by a factor equal to the material's dielectric constant
161
capacitance due to dielectric material eq
C' = κC
C' = new capacitance
162
can a dielectric material decrease the capacitance?
never
constant can never be less than 1
163
dielectrics in isolated capacitors
* shields the opposite charges from eachoterh
* increase in capacitance arises from decrease in voltage
164
dielectrics in circuit capacitors
increase in capacitance arises from increasee in stored charge
165
Cs ___ as more capacitors are added
decreases
166
Cp ___ as more capacitors are added
increases
167
describe what happens to capacitors in series
* capacitors must share the voltage drop in the loop and therefore cannot store as much charge
* group of capacitors act like one equivalent capacitor with a larger distance between its plates
* inc distance = smaller capacitance
168
voltage and capacitance eqs
capacitors in series
Vs = V1 + V2 + V3 + ... + Vn
1/Cs = 1/C1 + 1/C2 + 1/C3 + ... + 1/Cn
169
voltage and capacitance eqs
capacitors in parallel
Vp = V1 + V2 + V3 + ... + Vn
Cp = C1 + C2 + C3 + ... + Cn
170
assuming the plates are attached by a conducting material, how does a capacitor behave after the voltage source has been removed from a circuit?
the capacitor discharges, providing a current in the opposite direction of the initial current
171
ammeters
inserted in a series in a circuit to measure current
have negligible resistance
172
voltmeter
inserted in parallel in a circuit to measure a voltage drop
have very large resistances
173
ohmmeters
inserted around a resistive element to measure resistance
have negligible resistance
174
When you draw a battery, the larger line indicates that it is positive or negative?
The larger line in a battery symbol indicates that it is positive.
175
What equation typifies the definition of Current (I)?
I = ΔQ / Δt
```
I = Current
ΔQ = Change in charge
Δt = Change in time
```
176
True or False? Charges move more slowly through a resistor than through the rest of the circuit.
False. Charges move at the same speed throughout the entire circuit. Adding a resistor will cause the entire circuit as a whole to have a slower current.
177
What equation is used to relate the Current (I1, I2, etc) across all of the resistors to the total Current (It) of a circuit when resistors are in series?
It = I1 = I2 = In
178
The total Voltage for a circuit with resistors in parallel is equal to 3.2 V. If R1 = 2.3 Ω, R2 = 6.5 Ω, and R3 = 9.7 Ω, what is the current that is going through R3 (I3)?
(A) 3.29
(B) 1.33
(C) 2.04
(D) 0.33
(D) 0.33
```
V3 = Vt
V3 = 3.2 V
```
```
V3 = I3R3
3.2 = I3(9.7)
I3 = 3.2 / 9.7
I3 = 0.33 C/s
```
179
You have a simple circuit that contains a single resistor. If you increase the voltage, which of the following is true?
I. Resistance increases.
II. Current increases.
III. Capacitance increases.
(A) I Only
(B) II Only
(C) I and II Only
(D) II and III Only
(B) II Only
If you increase the voltage, the current will increase. Resistance (if it is an Ohmic material) will remain the same as it is a property that is dependent solely on the resistor and not on the battery or wire of the circuit.
180
How are Resistivity (ρ) and Conductivity (σ) related?
ρ = 1/σ
181
True or false? Nonionic solutions will always have a higher Resistivity than Ionic solutions.
True. Nonionic solutions will always have a higher Resistivity than ionic solutions.
The converse is also true: Ionic Solutions always have a higher Conductivity than Nonionic solutions.
182
What happens to resistance as the area of the resistor is increased? Why?
Resistance will decrease as area increases due to the increased number of paths that the electrons can take through the resistive material.
183
What happens to resistance as the length of the resistor is increased? Why?
Resistance will increase as length increases due to the longer amount of time that the electrons will need to travel through resistive material.
184
The Electrolytic Resistivity refers to what?
The resistivity of a liquid that can conduct electricity.
185
# Fill in the blanks: Resistors in ______________ must have the same Voltage, but may have different currents. Resistors in __________ must have the same current, but may have different Voltages.
(A) Series, Parallel
(B) Parallel, Series
(C) Series, Non-Ohmic Circuits
(D) Parallel, Non-Ohmic Circuits
(B) Parallel, Series
Resistors in Parallel must have the same Voltage, but may have different currents. Resistors in Series must have the same current, but may have different Voltages.
186
Draw the symbol for a capacitor in a circuit.
187
True or False. The plates charge this way because the positive terminal will send out protons to the plate it is attached to while the negative terminal will send out electrons to the plate it is attached to.
False. Protons do not move! The electrons from the plate attached to the positive terminal will be attracted to the positive terminal, sent through the battery, and then pushed away from the negative terminal to the plate attached to the negative terminal.
188
True or False? Capacitor Plate A is parallel and opposite to Plate B. If Plate A is twice the thickness of Plate B, it will store twice as much charge.
False. No matter their size or shape, 2 plates parallel and opposite of each other will always store equal and opposite amounts of charge.
189
You increase the charge on a Capacitor; therefore, the:
I. Capacitance increases
II. Voltage increases
III. Resistance increases
(A) I Only
(B) II Only
(C) I and II Only
(D) II and III Only
(B) II Only
You increase the charge on a Capacitor; therefore, the Voltage increases. The capacitance (just like resistance) will only change if you change its intrinsic characteristics.
190
Which of the following best describes the electric field between parallel capacitor plates?
(A) Unpredictable
(B) Linear
(C) Radial
(D) Uniform
(D) Uniform
There will be a uniform electric field between the parallel Capacitor plates, due to the separation and alignment of charges.
191
What is the equation for Capacitance in terms of its intrinsic characteristics?
C = ε₀ (A / d)
```
C = Capacitance
ε₀ = Permittivity of Dielectric (8.84⋅10^-12)
A = Area of each plate
d = Distance between the two plates
```
192
What equation can be used to calculate the total amount of energy produced by a capacitor when it is discharged in terms of the charge built up on one of the capacitor plates?
E = Q(V/2)
```
E = Total Energy produced by Capacitor
Q = Charge on one plate of capacitor
V = Voltage difference between the two plates of a capacitor
```
193
d
194
c
195
c
196
b
197
b
198
c
199
You have three capacitors in series (C1 = 2.6 F, C2 = 7.4 F, C3 = 2.2 F) and connected to a battery (V = 13.3 V). What is the voltage across C3?
(A) 3.12
(B) 6.05
(C) 13.24
(D) 19.44
(B) 6.05
```
1/Ceq = 1/C1 + 1/C2 + 1/C3
1/Ceq = 1/2.6 + 1/7.4 + 1/2.2
1/Ceq = approx. 1 (actual: .974)
Ceq = approx. 1 (actual: 1.03)
```
```
Ceq = Q / V
1.03 = Q / 13.3
Q = approx. 13.3 (actual: 13.7)
```
```
C3 = Q / V3
2.2 = 13.3 / V3
V3 = approx. 6 (actual: 6.05)
```
200
Recall the equation for the charge on a Capacitor. What happens to the Capacitance if the Charge is doubled?
(A) The Capacitance Quadruples
(B) The Capacitance Doubles
(C) The Capacitance stays the same
(D) The Capacitance is cut in half
(C) The Capacitance stays the same
The equation for charge on a Capacitor is Q = CV. Capacitance is constant for a given Capacitor, so if charge doubles, then the voltage would double.
201
You have three capacitors in parallel (C1 = 2.6 F, C2 = 7.4 F, C3 = 2.2 F) and connected to a battery (V = 13.3 V). What is the voltage across C3?
(A) 2.56
(B) 7.09
(C) 13.30
(D) 21.34
(C) 13.30
The voltage across each capacitor is exactly the same in a parallel configuration.
202
Why is the voltage across each capacitor exactly the same for each capacitor in a parallel configuration?
The voltage across each capacitor is exactly the same as the overall voltage because each capacitor is directly linked to the battery and every spot along a wire that isn't interrupted by either a resistor or a capacitor will have the exact same voltage in it.
203
You have three capacitors in parallel (C1 = 2.6 F, C2 = 7.4 F, C3 = 2.2 F) and connected to a battery (V = 13.3 V). What is the charge on a plate of C3?
(A) 12.27
(B) 18.79
(C) 29.26
(D) 48.30
(C) 29.26
```
C3 = Q3 / V
2.2 = Q3 / 13.3
Q3 = approx. 30 (actual: 29.26)
```
204
Which of the following are the main purposes for a Capacitor on the MCAT?
I. Creating uniform Electric Fields
II. Regulating the movement of Charges within a Circuit
III. Storing Electrical Potential Energy
(A) I only
(B) I and II only
(C) I and III only
(D) II and III only
(C) I and III only
The main purposes of a Capacitor on the MCAT are to create Uniform Electric Fields and Storing EPE.
205
Write out the equation for the Electrical Potential Energy stored by a Capacitor.
PE = 1/2QV
```
PE = Potential Energy stored by Capacitor
Q = Charge
V = Voltage difference between the two plates of a capacitor
```
206
What is a Dielectric? Why do we place Dielectrics between capacitor plates?
A Dielectric is a non-conducting (insulating) material. We place them between capacitor plates to prevent them from touching, which if they did touch, they would no longer store charge but rather just be part of the circuit, allowing charge to flow through them.
207
When a capacitor remains connected to a battery, adding a dielectric will:
I. Increase the voltage
II. Increase the charge
III. Increase the capacitance
(A) I Only
(B) III Only
(C) I and III Only
(D) II and III Only
(D) II and III Only
A dielectric will increase the capacitance of a capacitor, which will allow more charge to build up on the capacitor. This is because the induced polarization within the dielectric will effectively cancel out the charges on the plates, making the voltage difference between the two plates smaller. The battery will then add more charge to the plates in order to once again make the voltages equal, leaving the voltage unchanged while increasing the number of charges on each plate.
208
c
209
a
210
c
211
B
212
c
213
b
214
electrochemical cells
contained systems in which redox reactions occur
3 types: galvanic cells, electrolytic cells, concentration cells
215
electrodes
strips of metal or other conductive materials placed in an electrolyte solution
where oxidation and reduction take place
216
anode
site of oxidation
attracts anions
217
cathode
site of reduction
attracts cations
218
electrons flow from \_\_anode/cathode\_\_ to \_\_anode/cathode\_\_
anode to cathode
| (alphabetical order)
219
current flows from \_\_anode/cathode\_\_ to \_\_anode/cathode\_\_
cathode to anode
220
emf \> 0
cell is able to release energy (ΔG\<0) -\> spontaneous
221
emf \< 0
cell must absorb energy (ΔG \> 0) - nonspontaneous
222
galvanic cells
aka voltaic cells
house spontaneous reactions with a positive electromotive force
223
electrolytic cells
house nonspontaneous reactions with a negative electromotive force
require input of energy
can be used to create useful products through electrolysis
224
concentration cells
specialized form of galvanic cell in which both electrodes are made of the same material
concentration gradient between the two solutions causes the movement of charge (instead of potential difference)
225
makeup of galvanic cell
* two electrodes of distinct chemical identity - placed in separate compartment called half cells
* electrodes connected by conductive material
* ex: copper wire
* electrolyte solution surrounds each of the electrodes
226
electrolyte
composed of cations and anions
surrounds the electrodes in galvanic cells
227
salt bridge
inert salt that connects the two solutions around electrodes
permits the exchange of cations and anions
228
what would happen to galvanic cell without a salt bridge?
reaction would stop because an excess positive charge would build up on the anode, and an excess negative charge would build up on the cathode
229
cell diagram notation
anode | anode solution (concentration) || cathode solution (concentration) | cathode
|| = presence of salt bridge or other barrier
| = phase boundary
230
electrolysis
redox reaction driven by an eternal voltage source
231
makeup of electrolytic cell in comparison to galvanic cell
external voltage source (battery)
half reactions don't need to be separated into different compartments because the desired reaction is nonspontaneous
232
reactions that involves the transfer of n electrons per atom M
Mn+ + n e- --\> M (s)
one mole of metal M (s) will be produced if n moles of electrons are supplied to one of Mn+
233
electrodeposition eq
helps determine the number of moles of element being deposited on a plate
mol M = It/nF
mol M = amount of metal ion being deposited at a specific electrode
I = current
t = time
n = number of electron equivalents for a specific metal ion
F = faraday constant
234
how to calculate the voltage in concentration cell
nernst eq
235
rechargeable cell/battery
electrochemical cells that can experience charging (electrolytic) and discharging (galvanic) states
ranked by energy density
236
lead-acid battery
* when discharging: consist of a Pb anode and a PbO2 cathode in a concentrated sulfuric acid solution
* when charging: PbSO4- plated electrodes are dissociated to restore the original Pb and PbO2 electrodes and concentrate the electrolyte
* have low energy density
237
energy density
measure of a battery's ability to produce power as a function of its weight
238
nickel-cadmium batteries (Ni-Cd)
* when discharging: Cd anode and NiO(OH) cathode in a concentrated KOH solution
* when charging: Ni(OH)2 and Cd(OH)2 plated electrodes are dissociated to restore the of ones and concentrate the electrolyte
* have higher energy density that lead acid batteries
239
nickel-metal hydride (NiMH) batteries
today replace Ni-Cd batters bc they have higher energy density, are more cost-effective, and are significantly less toxic
240
surge current
above average current transiently released at the beginning of the discharge phase
wanes rapidly until a stable current is achieved
241
anode of galvanic cell is considered the \_\_pos/neg\_\_ electrode bc...
negative electrode because it is the source of electrons
242
cathod of galvanic cell is considered the \_\_pos/neg\_\_ electrode
positive electrode
243
anode of electrolytic cell is considered the \_\_pos/neg\_\_ electrode bc...
positive bc it is attached to the positive pole of the external voltage source and attracts anions from the solution
244
cathode of electrolytic cell is considered the \_\_pos/neg\_\_ electrode bc...
negative electrode bc its attached to the negative pole of the external voltage source and attracts cations
245
cathode attracts...
cations
246
anode attracts...
anions
247
isoelectric focusing
technique used o separate amino acids or polypeptides based on their isoelectric points (pI)
248
249
250
which type of cell has a positive ΔG?
electrolytic cells
251
which type of cell has a positive Ecell?
galvanic cells
252
reduction potential
quantifies the tendency for a species to gain electrons and be reduced
253
the higher the reduction potential...
the more a given species wants to be reduced - the more likely it is to be reduced
254
standard reduction potential
E°red
calculated by comparison to the standard hydrogen electrode (SHE) under standard conditions
255
standard electromotive force
emf or E°cell
the difference in standard reduction potential between the two half cells
256
for galvanic cells, the difference of the reduction potentials of the two half reactions is \_\_pos/neg\_\_
positive
257
for electrolytic cells, the difference of the reduction potentials of the two half reactions is \_\_pos/neg\_\_
negative
258
for galvanic cells the electrode with the more positive reduction potential is the \_\_anode/cathode\_\_
cathode
species with stronger tendency to gain elections is actually doing so - spontaneous rxn
259
for galvanic cells the electrode with the less positive reduction potential is the \_\_anode/cathode\_\_
anode
species with stronger tendency to gain elections is actually doing so - spontaneous rxn
260
for electrolytic cells, the electrode with the more positive reduction potential is the \_\_anode/cathode\_\_
anode
bc it is forced to be oxidized by the external voltage source
261
for electrolytic cells, the electrode with the less positive reduction potential is the \_\_anode/cathode\_\_
cathode
bc it is forced to be reduced by the external voltage source
262
standard electromotive force eq in terms of reduction potentials
E°cell = E°red,cathode - E°red,anode
263
if a cell's electromotive force is denoted as positive value, what does that mean?
cell is spontaneous (Galvanic)
264
if a cell's electromotive force is denoted as negative value, what does that mean?
cell is nonspontaneous (electrolytic)
265
1. electrolytic bc neg emf
2. galvanic bc pos emf
266
when E°cell is positive, ΔG° is:
type of electrochemical cell:
negative
galvanic cell
267
when E°cell is negative, ΔG° is:
type of electrochemical cell:
positive
electrolytic cell
268
when E°cell is 0, ΔG° is:
type of electrochemical cell:
0
concentration cell
269
nernst eq describes...
the relationship between the concentration of species in a solution under nonstandard conditions and the electromotive force
270
when Keq \> 1, E°cell is
positive
271
when Keq \< 1, E°cell is
negative
272
when Keq = 1, E°cell is
0
273
eq relating ΔG° and emf
ΔG° = -nFE°cell
n = number of moles of electrons exchanged
274
simplified nernst eq
Ecell = E°cell - (0.0592/n)logQ
E°cell = emf under standard conditions
n = number of moles of electrons
Q = reaction quotient
275
standard change in free energy from equilibrium constant eq
ΔG° = -RTlnKeq
276
free energy change under nonstandard conditions eq
ΔG = ΔG° + RTlnQ
277
278
What is the purpose of a salt bridge?
The purpose of a salt bridge is to neutralize the charges in the solutions that are either becoming positive or negative as the reaction proceeds. This allows the reaction to continue moving forward.
279
For a Redox Reaction to be spontaneous, which of the following must its voltage be?
(A) Positive
(B) Zero
(C) Non-Zero [positive or negative]
(D) Negative
(A) Positive
For a Redox Reaction to be spontaneous, the voltage must be positive.
280
What equation can be used to determine the Standard Cell Potential for a Galvanic Cell?
E°cell = E°red (cathode) - E°red (anode)
281
True or false? The deposition of the metal from the electrolyte solution onto the cathode is called Galvanization, explaining the alternate name for these cells.
True. The deposition of the metal from the electrolyte solution onto the cathode is called Galvanization, explaining the alternate name for these cells.
282
You are reducing copper, and decide to double the number of moles of copper that you are reducing. If you do so, the:
I. ∆G° will double
II. E°red for copper will double
III. K will double
(A) I Only
(B) II Only
(C) I and II Only
(D) I and III Only
(A) I Only
You are reducing copper, and decide to double the number of moles of copper that you are reducing. If you do so, the ∆G° will double and n will double, leaving the E°red as the same value according to the relationship ∆G° = -nFE°cell. K will not change according to the relationship -nFE°cell = -RTlnK.
283
Cu2+ (E°red = .34) and Zn2+ (E°red = -.76) are both part of a Galvanic Cell. What is the equilibrium constant K for this cell?
(A) 3.05⋅10^6
(B) 8.90⋅10^14
(C) 6.03⋅10^33
(D) 1.59⋅10^37
(D) 1.59⋅10^37
```
E°cell = E°red (cathode) - E°red (anode)
E°cell = .34 - -.76
E°cell = 1.10
```
```
E°cell = (.0592 / n)logK
1.10 = (.0592 / 2)logK
logK = approx. 40 (actual: 37.2)
K = approx. 1⋅10^40 (actual: 1.59⋅10^37)
```
284
The Nernst Equation allows us to relate E°cell to Ecell. Write out this equation.
Ecell = E°cell - (.0592 / n)logQ
285
Cu2+ (E°red = .34) with a concentration of 3.2⋅10^-3 M and Zn2+ (E°red = -.76) with a concentration of 4⋅10^-5 M are both part of a Galvanic Cell. What is Ecell for this cell under these conditions?
(A) .54
(B) .95
(C) 1.06
(D) 1.16
(D) 1.16
```
E°cell = E°red (cathode) - E°red (anode)
E°cell = .34 - -.76
E°cell = 1.10
```
```
Ecell = E°cell - (.0592 / n)logQ
Ecell = 1.1 - (.0592 / 2)log(4⋅10^-5 / 3.2⋅10^-3)
Ecell = 1.1 - (.0296)log(approx. .01 (actual: .0125)
Ecell = 1.1 - (.0296)(approx. -2 (actual: -1.903))
Ecell = 1.1 - (.approx. -.05 (actual: -.056))
Ecell = approx. 1.15 (actual: 1.156)
```
286
True or false? Concentration cells often overshoot their equilibrium point where concentrations are equal, reversing which electrode is the cathode and anode and reversing the current.
False. Concentration Cells will work until equal concentrations in each compartment is achieved, and then there is no Electrical Potential Energy or the ability to do further work.
287
b
288
B
289
c
290
A
291
A
292
B
293
A
294
D
