Exam 1 Flashcards
q=Ne
q=
charge
q=Ne
N=
number of electrons
q=Ne
e=
charge on a single electron
charge is a _____ force
conservative
if an object is polarized, it means…
charges shift in a neutral object
conductors vs insulators
conductors:
metals
allow e- to transfer
insulators:
plastic
hold e- more tightly
µ =
10^-6
F=k (q1q2/r^2)
F=
force
F=k (q1q2/r^2)
k=
Coulomb’s constant
9x10^9
F=k (q1q2/r^2)
q=
charge on that specific object
F=k (q1q2/r^2)
r=
the distance between q1 and q2
given q=18µC and d=15cm, find magnitude and direction on force 1.
q1 = +q
q2 = -2.0q
q3 = +3.0q
-3.00µC in the center of a compass. 2 additional charges are on the center (r=.100m). -4.0µC due north and +5.0µC due east.
find the direction and magnitude of the charge in the center.
an electron moves at 8.5x10^5m/s. what is the radius?
+q placed in an electric field will accelerate _____ the field (gravity)
with
-q placed in an electric field will accelerate _____ the field (gravity)
against
density of electric field lines relates to the ______ of E
magnitude
2 point charges are placed on an x-axis. -5.5µC at the origin and 8.5µC ar x=10cm.
what is the net electric field at x=-4cm?
2 point charges are placed on an x-axis. -5.5µC at the origin and 8.5µC ar x=10cm.
what is the net electric field at x=4cm?
2 point charges are placed on an x-axis. -5.5µC at the origin and 8.5µC ar x=10cm.
where is the net field =0?
E+ = E-
0.41m left
an electron enters a capacitor with v=5.75x10^6m/s. it has a downward distance of d=0.638 and a horizontal length of 2.25cm.
what is the magnitude of the electric field?
an electron is placed between plates of a parallel plate capacitor. when released, it remains balanced.
what is the magnitude and direction of the electric field
F=ma
FE-Fg = 0
FE=Fg
qE=mg
E=mg/q
E= 5.58x10^-11 N/C downward
an electron is placed between plates of a parallel plate capacitor. when released, it remains balanced.
if gravity is turned off, what is the acceleration if a proton is released?
F=ma
0-FE=ma
-qE=ma
a=-qE/m
a=5.34x10^-3 m/s^2 downward
ideal conductors have
_____ charge
fields _____ and at _____
and _____ shielding
excess
inside and at surface
electron shielding
point charge:
E=kd/r^2
voltage = ________
electrical potential
do you use signs in k(q1q2/r^2)
NO!
moving against gravity = ______ height
gaining
moving against electric field = ______ voltage
gain
moving with the electric field = ______ voltage
lose
W = -q∆V
W=
work
W = -q∆V
q=
charge
W = -q∆V
V=
change in potential/voltage
E=- ∆V/∆d
E=
electric field
E=- ∆V/∆d
V=
potential difference
E=- ∆V/∆d
d=
distance between plates
____ decreases when you move with gravity
height
______ decreases when you move with the electric field
potential/voltage
a ______ mass accelerates against the gravitational field from a high to low gravitational height
positive
a positive mass accelerates _____ the gravitational field form a high to low gravitational height
against
a ______ charge accelerates with the electric field from a high to low electrical height
positive
a positive charge accelerates _____ the electric field from a high to low electrical height
with
a positive charge is moving with the field
q∆V = -We = ∆EPE
q∆V = -We = ∆EPE
+ - - (+) -
a negative charge is moving with the field
q∆V = -We = ∆EPE
q∆V = -We = ∆EPE
- - - (-) +
a positive charge is moving against the field
q∆V = -We = ∆EPE
q∆V = -We = ∆EPE
+ + - +
a uniform electric field points in the negative y and magnitude of 4300N/C
what is the electrical potential difference between Vb-Va?
0V
a uniform electric field points in the negative y and magnitude of 4300N/C
what is the electrical potential difference between Vc-Vb?
∆V=E∆d
344V
a uniform electric field points in the negative y and magnitude of 4300N/C
what is the electrical potential difference between Va-Vc?
∆V=E∆d
-344V
energy conservation:
1/2mva^2 + qVa = 1/2mvb^2 + qVa
electrons in a tv set accelerate from rest at point A at a potential difference of 25kV to point B
_____ has the higher potential energy
B
electrons in a tv set accelerate from rest at point A at a potential difference of 25kV to point B
the electric field points from _____
B -> A
electrons in a tv set accelerate from rest at point A at a potential difference of 25kV to point B
what is the speed of the electrons when they arrive at B?
finding the electrical potential for a point charge:
V=k (q/r)
equipotential surfaces are always _____ to electrical field lines
perpendicular
height _____ when moving away from the center
decreases
+4.0µC is placed at x=0 and -8µC 10cm to its right.
what is the potential at the midpoint?
what is the potential at 15cm?
a charge A of -3.0µC is fixed. from a horizontal distance of 0.0450m, a particle with mass 7.20x10^-3kg and a charge of -8.0µC is fired with an initial speed 165m/s towards a fixed charge (B).
how far from charge is the particle when the speed is
(a) 150m/s?
(b) 0m/s?
x=0.25m and y=0.16m
how much work is needed to assemble all 3 charges?
describe a capacitor
has “capacity” to store both electrical charge and energy (via) field
capacitors are dependent on _____ and _____
geometry
composition
describe a dialectric
“stomps down” the electric field by polarization (trash back example)
Ohm’s law: V=IR
V=
voltage
Ohm’s law: V=IR
I=
current
Ohm’s law: V=IR
R=
resistance
low voltage = _____ resistance
low
2 ways to change resistance
geometry
composition
R=p L/A
R=
resistance of a wire
R=p L/A
p=
resistivity
R=p L/A
L=
length
R=p L/A
A=
cross sectional area
more resistance = _____ resistance
less
increased area = _____ resistance
decreased
increased length = _____ resistance
increased
conductors _____ resistance
decrease
inductors _____ resistance
increase
an average tv set runs 6 hours a day. calculate the yearly cost of 100 million TVs when power consumptions is 165W and it costs 12.5c kW/hr
junction rule:
Iout = Iin
loop rule:
Vdrop = Vgain
big loop clockwise:
Vdrop = Vgain
5I2 + 18V + 10I3 = 13V
left loop counterclockwise:
Vdrop = Vgain
13V = 5I2 + 2V + 10I2
right loop counterclockwise:
Vdrop = Vgain
18V + 10I3 = 2V + 10I2
ammeters connect in _____ so there is _____ resistance
series
zero
voltmeters connect in _____ so there is _____ resistance
parallel
infinite
F=qe
F=
force
F=qE
E=
electric field intensity
F=qvB
v=
velocity
F=qvB
B=
magnetic field intensity
right hand rule:
thumb is _____
fingers are _____
palm faces _____ and is ______
velocity
field
up, force
motion of charge in a B field?
F=ma
qvB=m(v^2/r)
r=mv/qB
a charged conductor is brought near an uncharged insulator. what happens to the objects?
they attract eachother
consider 3 identical spheres, A, B, and C. sphere A carries a charge of -2.0µC; sphere B carries a charge of -6.0µC; and sphere C carries a charge of +4.0µC. Sphere A and B touch and then separate. Sphere B and C touch and then separate.
What is the charge on C?
0
a -4.0µC charge is located 0.4m to the left of a +6.0µC charge. what is the magnitude and direction of the electrostatic force on the positive charge?
an electron is located between the plates of a parallel plate capacitor. what is the magnitude and direction of the electronic field such that the electric force exactly balances the weight of the electron so it remains stationary?
qE=mg
E=mg/q
E=5.6x10^-11 N/C
the electron volt is a unit of _____
energy
as an electron moves against an electric field, its electric potential _____ and potential energy ______
increases
decreases
2 point charges are held at the corners of a rectangle. h=0.050m and w=0.15m. what is the electric potential at point A?
what is the change in electric potential when a charge of -1.0µC is moved from A to F to C to E?
what way does the electric field point?
D
the potential difference across the ends of a wire doubles in magnitude. how does this effect the resistance?
no change
can only be changed by geometry or composition
resistors in series have the same _____ through them
current
resistors in parallel have the same ______ through them
voltage
for resistors in parallel the total resistance is _____ any singular resistors
less than
for resistors in series, the total resistance is ______ any single resistor
greater than
what is the total resistance of the circuit?
what is the current through the 1.8Ω resistor?
a) 3.3
b) 2.8
c) 14
d) 6.9
e) 5.6
V=IR
Ibat = V/R
25/7.5 = 3.33A
I1.8 must be < I bat so
2.8
the length of a wire is kept the same but the radius is doubled. this causes the resistance to ______ by a factor of ______
decrease
4
a 4A circuit is maintained in a simple circuit with a total resistance of 2Ω. how much energy is delivered in 45s?
V=IR
V=(4)(2) = 8V
P=IV
P=(4)(8) = 32W
P=energy/time
energy=Pt
(32)(45) = 1440J
if the current is 2A, what is the voltage?
V=IR
(2)(3) = 6V
kirchoff’s loop rule is a statement of the law of conservation of _____
energy
left loop clockwise
Vdrop = Vgain
12I2 + 8I2 = 4V + 6V
right loop clockwise
Vdrop = Vgain
4V + 2V = 6I3 + 8I2
whole loop clockwise
Vdrop = Vgain
12I2 + 2V = 6I3 + 6V
