FINAL EXAM Flashcards
a charged conductor is brought near an uncharged insulator. which of the following statements is true?
a. both objects will repel
b. both objects will attract
c. neither object exerts an electrical force on the other
d. the objects will repel each other only if the conductor has a negative charge
e. the objects will attract each other only if the conductor has a positive charge
b
both positive and negative charges attract a neutral object
consider 3 identical metal spheres, A, B, and C. sphere A carries a charge of -2.0uC; sphere B carries a charge of -6.0uC; and sphere C carries a charge of +4.0uC. spheres A and B are touched together and then separated. spheres B and C are then touched and separated. does sphere C end up with an excess or deficiency of electrons, and how many is it?
a. deficiency, 6x10^13
b. excess, 3x10^13
c. excess, 2x10^13
d. deficiency, 3x10^12
e. there is no excess or deficiency of electrons
e
all have -4uC
a -4.0uC charge is located 0.45m to the left of a +6.0uC charge. what is the magnitude and direction of the electrostatic force on the positive charge?
a. 2.2N to the right
b. 2.2N to the left
c. 1.1N to the right
d. 1.1N to the left
e. 4.4N to the right
d
an electron is located between the plates of a parallel-plate capacitor. what is the magnitude and direction of the electric field such that the electric force exactly balances the weight of the electron so that it remains stationary?
at what point(s) in the vicinity of the fixed charges shown could a third charge of +2q be placed so that the net electrostatic force on it would be zero?
a. somewhere on the x-axis to the right of the +4q charge
b. somewhere on the x-axis between the 2 charges, but nearer to the -2q charge
c. somewhere on the x-axis to the left of the -2q charge
d. somewhere on the x-axis between the 2 charges, but closer to the +4q charge
e. at 2 points along the x-axis, one such point is to the left of the -2q charge and the other is to the right of the +4q charge
c
complete the following statement: the electron-volt is a unit of
a. electric field
b. charge
c. energy
d. electric potential
e. electric force
c
measured in J
as an electron moves against an electric field,
a. its electrical potential decreases and its potential energy increases
b. its electrical potential increases and its potential energy increases
c. its electrical potential increases and its potential energy decreases
d. its electrical potential decreases and its potential energy decreases
e. its electrical potential remains constant and its potential energy increases
c
two point charges are held at the corners of a rectangle as shown in the figure. the rectangle has a height of 0.050m and a width of 0.150m. determine the electric potential at corner A.
what direction is the electric field at B?
towards D
what is the change in electric potential energy when a charge of -1.0uC is moved from A to F to C to E?
a. -7.0x10^-5J
b. 7.0x10^-5J
c. 3.0x10^-5J
d. -3.0x10^-5J
e. -4.0x10^-5J
b
EPE=qV
= q (Vf - Vi)
= (-1x10^-6)(-40-(30))
= 7.0x10^-5J
the potential difference across the ends of a wire is doubled in magnitude. which of the following statements concerning the resistance of the wire is true?
a. the resistance increases by a factor of 4
b. the resistance increases by a factor of 2
c. the resistance is not changed
d. the resistance decreases by a factor of 2
e. the resistance decreases by a factor of 4
c
R=p(L/A)
resistors in series have the same (voltage / current) through them
current
resistors in parallel have the same (voltage / current) across them
voltage
for resistors in parallel, the total resistance is (greater than / equal to / less than) the value of any single resistor
less than
what is the equivalent resistance of the circuit?
7.5
what is the current through the 1.8 resistor?
a. 3.3A
b. 2.8A
c. 14A
d. 6.9A
e. 5.6A
2.8A
Vbat=IR = 3.33A
I1.8 < Ibat, so must be b
what is the potential drop across the 3.5 resistor?
a. 17V
b. 25V
c. 8.0V
d. 2.0V
e. 5.0V
V = IR
(0.55)(3.6) = 2.0V
the length of a certain wire is kept the same while its radius is doubled. what is the change in resistance of the wire?
a. the resistance increases by a factor of 4
b. the resistance increases by a factor of 2
c. the resistance is not changed
d. the resistance decreases by a factor of 2
e. the resistance decreases by a factor of 4
e
A=πr^2
geometry and composition
a 4A current is maintained in a simple circuit with a total resistance of 2. how much energy is delivered in 45 seconds?
P=IV
V=IR = (4A)(2) = 8V
P= (4A)(8V) = 32W
P = energy/time
energy = Pt = (32J/s)(45s) = 1440J
2 resistors are connected in parallel, and the combination connected to a DC power supply with voltage V as shown. if the current shown is 2A, what is the value of the battery voltage?
6V
R=3
V=IR = (2A)(3) = 6V
Kirchhoff’s loop rule is a statement of
a. the law of conservation of momentum
b. the law of conservation of charge
c. the law of conservation of energy
d. the law of conservation of mass
e. Newton’s second law
c
which of the following equations corrected represents a use of Kirchhoff’s loop rule for the circuit shown?
a. 2V = (6)I3 + 6V + (12)I1
b. 4V = (8)I2 + (12)I1
c. 4V + 6V + (12)I1 = (8)I2
d. 4V + 6V = (12)I1 + (8)I2
e. none of these
d
which of the following statements concerning permanent magnets is false?
a. the North Pole of a permanent magnet is attracted to the South Pole
b. all permanent magnets are surrounded by a magnetic field
c. the direction of the magnetic field is indicated by the North Pole of a compass
d. magnetic field lines outside a permanent magnet originate from the north pole and the end on the south pole
e
no magnetic monopoles
two particles move through a uniform magnetic field as shown. which of the following statements concerning these particles is true?
a. the particles may both me neutral
b. particle 1 is positively charged, 2 negatively
c. particle 1 is positively changed, 2 positively
d. particle 1 is negatively charged, 2 negatively
e. particle 1 is negatively charged, 2 positively
d
both CCW - same sign charges
a charged particle is moving in a uniform constant magnetic field. which of the following statements concerning the magnetic force exerted on the particle is false?
a. the magnetic force does no work on the particle
b. the magnetic force changes the velocity of the particle
c. the magnetic force can only act on a particle in motion
d. the magnetic force increases with the speed of the particle
e. the magnetic force does not change the kinetic energy of the particle
d
uniform circular motion
an electron moves with a speed of 8.0x10^6m/s. it enters a region where there is a magnetic field of 2.5T, directed at an angle of 60° to the velocity. calculate the magnitude of the magnetic force on the electron
F=qvBsinθ
F=(1.6x10^-19C)(8.0x10^6m/s)(2.5T)sin60
F=2.8x10^-12N
a proton is shot into a region containing both an electric field (shown) and a magnetic field (not shown). if the proton moves undeflected through the region with the fields, in what direction is the magnetic field?
into the page
a long straight wire carries a 40.0A current in the +x direction. at a particular instant, an electron is moving at 1.0x10^7m/s in the +y direction from the wire.
1) what is the direction of the force on the electron at this instant?
2) what is the magnitude of the force on the electron at this instant if r=.10m?
1) +x direction
2) B = uoI/2πr
(1.6x10^-19)(10^7)[((4πx10^-7)(40))/2π(0.1))] = 1.28x10^-16N
two long, straight, parallel wires separated by 0.10m carry currents in opposite directions as shown in the figure. determine the total magnetic field at point C, midway between the wires
the three loops of wire shown are all subject to the same uniform magnetic field. loop 1 swings back and forth, loop 2 rotates about a vertical axis, and loop 3 oscillates up and down at the end of a spring. which loop, or loops, will have an induced emf?
loop 2
no change in B, A, or θ for 1,3
θ changes in loop 2
a long straight wire carries current I that is to the right and increasing with time. the induced emf in each of the loops is such that
a. no emf is induced in any loop
b. all loops experience a counter clowise emf
c. loop A has a counterclockwise emf, loop B has no induced emf, and loop C has a clockwise emf
d. loop A has a clockwise emf, loop B has no induced emf, and loop C has a counterclockwise wise emf
e. loop A has a counterclockwise emf, loop B has a clockwise emf, and loop C has a clockwise emf
d
when more x’s are added, you must add more ______ and the rotation is _____
dots
CCW
when more dots are added, you must add more _____ and the rotation is _____
x’s
CW
which of the following statements concerning transformers is FALSE?
a. a transformer that steps up voltage, steps down current
b. they are an application of Faraday’s and Lenz’s laws
c. a transformer can function with either an ac current or a dc current
d. a transformer can function with either an ac current or a dc current
e. their operation makes use of induced emfs
d
transformers can only be used for _____ circuits
AC
a variable capacitor is connected to an ac sources. what effect does decreasing the frequency of the circuit have on the capacitive reactance and current?
capacitor increases
current decreases
in the circuit shown in the drawing, the generator supplies the same amount of current at either very small or very large frequencies. what can be deduced about the resistances R, R2, and R3 from this information?
a. R1=R2=R3
b. R1 = 2R2
c. R1 = R2
d. R1 = R3
e. R2 = R3
d
at low frequencies, no _____
capacitor
at high frequencies, no _____
inductor
an electromagnetic wave propagates along the +y direction as shown. if the E-field at the origin is along the +z direction, what is the direction of the B-field?
a. +x
b. -x
c. +y
d. -7
e. +z
f. -z
a
right hand rule
right hand rule for waves
thumb = velocity
fingers = electric field
palm = magnetic field
list the electromagnetic waves from longest to shortest
radio waves, microwaves, infrared, visible, ultraviolet, x-ray, gamma
a student looks at their reflection in a convex mirror. which of the following statements concerning their image is true?
a) their image must be real
b) the image is farther from the ornament than the student
c) the image is larger than the student
d) the image must be inverted
e) the image must be smaller than the student
e
a convex mirror has an image that is _____, size is _____, and is a _____ image
upright
smaller
virtual
an object is 1.0m in front of a mirror. a virtual image is formed 10.0m behind the mirror. what is the radius of curvature of the mirror?
1/f = 1/do + 1/di
1/f = 1/1 + 1/-10 = 1.11m
R=2f =2.2m
the inverted image of a light bulb is formed on a screen located 9.00m from a spherical mirror. the image is 4.00x larger than the light bulb. determine the object distance and the type of mirror used.
m = -4 = -di/do
do = di/4 = 9/4 = 2.25
concave
the figure shows the path of a portion of a ray of light as it passes through three different materials. what can be concluded concerning the refractive indices of these 3 materials?
a) n1 < n2 < n3
b) n1 < n2 < n3
c) n3 < n1 < n2
d) n2 < n1 < n3
e) n1 < n3 < n2
c
a ray of light passes from air into a block of glass with a refractive index of 1.59 as shown in the figure. what is the value of the distance D?
n1sinθ1 = n2 sinθ2
1sin50 = 1.59sinθ2
θ2 = 28.8
tan θ2 = D/4
D = 4tan28.8 = 2.19m
an object is placed 21cm from a diverging lens with a radius of curvature of 50cm. what is the magnification of the resulting image?
f=-R/2 = -25cm
1/f = 1/do + 1/di
1/-25 = 1/21 + 1/di
di = -11.4cm
m = -di/do
m = -(-11.4)/21 = .54
the near point of a farsighted person is 65cm. what power contact lens must they use to correct this visual problem and be able to read a book at a normal near point of 25cm?
P = 1/f
1/f = 1/do + 1/di
I/f = 1/.25 + 1/-0.65 = 2.5 diopters
in a Young’s double slit experiment, green light is incident on the 2 slits. the interference pattern is observed on a screen. which of the following changes would cause the fringes to be more closely spaced?
a) reduce the slit separation of distance
b) use red light instead of green light
c) use blue light instead of green light
d) move the screen farther from the slits
e) move the light source farther away from the slits
c
what is the minimum (non-zero) thickness of a benzene (n=1.501) thin film that will result in constructive interference when viewed at a normal incidence and illuminated with orange light (λ=615nm)? A glass slide (ng=1.620) supports the thin film
0 = mλ
λ = λ/h = 615/1.501 = 409nm
2+ = m(λ/2) = (1)409/2 = 204nm
as an electron moves opposite to an electric field the electric potential _____ and its electrical potential energy _____
increases
decreases
a proton is shot with an initial speed of 2.50x10^5m/s towards P away from A. what will its speed just before hitting the plate at P?
two charges are placed on the x-axis. one charge is (q1=-13uC) is at x1=0cm and the other (q2=-39uC) is at x2=4.0cm.
what is the electric potential midway between the two charges
two charges are placed on the x-axis. one charge is (q1=-13uC) is at x1=0cm and the other (q2=-39uC) is at x2=4.0cm.
what would be the net electric field at 3.0cm to the right of the -13uC charge?
LONG ANSWER
a) what is the equivalent resistance of the circuit?
b) how much current flows through the 6.00 resistor?
c) what is the voltage across the 9.00 resistor?
d) how much energy does the 6.00 resistor use in 4 minutes?
what frequency limit will the current going through the resistor be the greatest?
a) very low frequencies
b) at the resonant frequency of the circuit
c) at very high frequencies
d) depends on the specific values of L and C
explain
c
at high frequencies the current doesn’t go through the inductor. at low frequency it doesn’t gp through C so would not reach the resistor on both sides
locate the image produced by a concave mirror with the object outside the focal point using the 3 rays discussed
inverted
real
locate the image produced by a concave mirror with the object located inside the focal point
upright
larger
virtual
locate the image produced by a convex mirror
upright
virtual
smaller
two long, straight wires separated by 0.10m carry currents of 18A and 6A.
a) determine the magnetic field, including its direction, at the point P midway between the wires
b) a proton is now placed at mid point P and directed towards the top of the page with a speed 2.3x10^5m/s. find the magnetic force on the proton at this instant
an electromagnetic wave has an electric field with an average (rms) value of 250N/C. what is the energy delivered to a surface with an area of 0.75m^2 by this wave in one hour?
a conducting bar moves to the left on two conducting rails as shown. as a result of the bar moving through a constant external magnetic field, a current I is induced in the indicated orientation. what is the direction of the external magnetic field? explain
out of page
with bar moving left, area of loop is DECREASING so you are either losting dots or losing x’s
you know that whichever change you have the induced current goes CCW to oppose so the B induced is adding dots, this pairs with the change of losing dots so the external field is OUT OF THE PAGE
a woman stands 2.0m in front of a mirror and notices that her upright image height is 1/4 her actual height
a) what type of mirror is being used and how do you know
b) determine the focal length of the mirror
a ray of light in air strikes a block of quartz at an angle of incidence of 30 degrees. the angle of refraction is 20 degrees. what is the speed of light in quartz?
a diamond ring (n=2.42) submerged in benzene (n=1.51)
a) what is the critical angle when light moves from the diamond to benzene?
b) what is the critical angle when light moves from benzene to the diamond?
a plastic plate (n=1.575) is submerged in ethyl alcohol (n=1.362)
what is the critical angle when light moves from ethyl alcohol to the plastic?
two glass plates are touching along the left edge and separated by a distance t on the right edge. when using light of wavelength 589nm, the 15th order dark fringe is observed to appear at the rightmost edge. what is the thickness of the air gap, t, on the right edge?
