Final Exam Flashcards
A thin uncharged conducting spherical shell has a charge q carefully placed at its center through a small hole in the shell. The charge q does not touch the shell. What is the charge on the shell?
0
Wire A and Wire B are each carrying the same current. If the diameter of Wire A is twice that of Wire B, how does the drift velocity vdA in Wire A compare to that in Wire B?
VdA= VdB/4
The internal resistances of an ideal voltmeter and an ideal ammeter are respectively (ideal meaning the behavior of the system is not changed when using the meter)?
Infinite and zero
Increasing the separation of the two charged parallel plates of a capacitor, which are disconnected from a batter will produce what effect on the capacitor?
Decrease capacitance
In a certain material there is a current of 16 A flowing through a surface to the right, and there is an equal amount of positive and negative charge passing through the surface producing the current. How much negative charge passes through the surface?
8 C/s toward the left
An uncharged conductor is supported by an insulating stand. I pass a positively charged rod near the left end of the conductor, but do not touch it. The right end of the conductor will be:
Positive
Three resistors connected in series have individual voltages labeled Delta V1, Delta V2, and Delta V3, respectively. Which of the following expresses the value of the total voltage (delta Vt) taken over the three resistors together?
Delta VT= Delta V1+ Delta V2 + Delta V3
Which of the following characteristics are held in common by both gravitational and electrostatic forces when dealing with either point masses or charges?
All of the above
A resistor is connected to a battery with negligible internal resistance. If you replace the resistor with on e that has twice the resistance, by what factor does the power dissipated in the circuit change?
.50
Which is a unit of power?
J/s
A repelling force must occur between two charged objects under which conditions?
Charges are of like signs
If body M, with a positive charge, is used to charge body N by induction, what will be the nature of the charge left on the latter?
Must be negative
If body P, with a positive charge, is placed in contact with body Q (initially uncharged), what will be the nature of the charge left on Q?
Must be positive
I wish to use a positively charged rod to charge a ball by induction. Which statement is correct?
The ball must be a conductor
Electric field is dimensionally equivalent to which of the following?
N/C
The number of electric field lines passing through a unit cross sectional area is indicative of:
Field Strength
Relative distribution of charge density on the surface of a conducting solid depends on
The shape of the conductor
Two identical balls have the same amount of charge, but the charge on ball A is positive and the charge on ball B is negative. The balls are placed on a smooth, level, frictionless table whose top is an insulator. Which of the following is true?
None of the above is correct
If a charge +Q is placed inside a hollow isolated conductor that is originally neutral and the charge does not touch that conductor at any time:
The outside surface of the conductor will become positively charged
The Millikan oil-drop experiment demonstrated that
The electronic charge is quantized
In the Millikan oil-drop experiment, it was found that oil droplets
Could have positive, negative, or zero net charge.
The unit of electrical potential, the volt, is dimmensionally equivalent to
J/C
A free electron is in an electric field. With respect to the field, it experiences a force acting:
anti-parallel (in opposite direction)
In which case does an electric field do positive work on a charged particle?
A negative charge moves opposite to the direction of the electric field
Doubling the voltage across a parallel plate capacitor does not double which of the following?
The energy stored
You measure a 25.0 V potential difference across a 5.00 ohm resistor. What is the current flowing through it?
5.00A
If a certain resistor obeys Ohm’s law, its resistance will change
None of the above, since resistance is a constant for the given resistor
Two cylindrical resistors are made of the same material and have the same resistance. The resistors R1 and R2 have different radii, r1 and r2, and different lengths, L1 and L2. Which of the following relative values for radii and legths would result in equal resistances?
2r1=r2 and 4L1=L2
Which process will double the power given off by a resistor?
doubling the current by making a resistance half as big
A resistor is made of a material that has a resistivity that is proportional to the current going through it. If the voltage across the resistor is doubled, what happens to the power dissipated by it?
It increases by a factor of 2^3/2
When the voltage across a nonohmic resistor is doubled, the current through it triples. What happens to the power delivered to this resistor?
The power increases to 6 times the original amount
Doug rubs a piece of fur on a hard rubber rod, giving the rod a negative charge, what happens?
Electrons are added to the rod
A repelling force must occur between two charged objects under which conditions?
Charges are of like signs
When a glass rod is rubbed with silk which of the following statements best describe what happens
Electrons are removed from the rod
When charging two objects by rubbing them together
They must be made of different material
Who was the first to determine the electron’s charge
Millikan
An uncharged conductor is supported by an insulating stand. I pass the positively charged rod near the left end of the conductor but do not touch it. The right end of the conductor will be
Positive
Of the following substances, which one contains the highest density of free electrons?
Iron
Which of the following best characterizes electrical conductors?
Electric charges move freely
Which of the following best characterizes electrical insulators?
Charges on the surface don’t move
I wish to use a positively charged rod to charge a ball by induction. Which statement is correct?
The ball must be a conductor
How can an uncharged object attract an uncharged object made of non-conducting material
The charges in the uncharged object can become polarized
Two point charges are 4 cm apart. They are moved to a new separation of 2 cm. By what factor does the resulting mutual force between them change?
4
If the distance between two charges is tripled, the mutual force between them will be changed by what factor?
1/9
If the size of the charge value is tripled for both of two point charges maintained at a constant separation, the mutual force between them will be changed by what factor?
9.0
The constant Ke is equivalent dimmensionally to which of the following?
Nm^2/C^2
The beam of electrons that hits the screen of an oscilloscope is moved up and down by:
Electrical charges on deflecting plates
The electric field of a point charge has an inverse ____ behavior
r^2
The electric field at the surface of a positively charged conductor has a given direction characterized by which of the following?
zero vector
The electric field associated with a uniformly charged hollow metallic sphere is the greatest at:
The sphere’s outer surface
At what point is the charge per unit area greatest on the surface of an irregularly shaped conducting solid?
Where curvature is greatest
If a conductor is in electrostatic equilibrium near an electrical charge:
The electric field inside the conductor must be zero
The combination of two separated point charges of opposite sign but equal magnitude is called
dipole
A charge +Q is placed inside a balloon and the balloon is inflated. As the radius of the balloon r increases the number of field lines going through the surface of the balloon:
stays the same
The quantity of electrical potential, the volt, is dimensionally equivalent to:
electric field x distance
A free electron is in an electric field. With respect to the field, it experiences a force acting:
anti parallel
opposite in direction
In which case does an electric field do positive work on a charged particle?
a negative charge moves opposite to the direction of the electric field
The distance between two negative point charges is increased by a factor of three, the resultant potential energy is what factor times the initial potential energy?
1/3
Which of the following characteristics are held in common by both gravitational and electrostatic forces when dealing with either point masses or charges?
all of the above choices are valid
Consider two charged spheres one with +2 C and the other with -2C. A proton is at the point halfway between the spheres. What is not zero?
the force on the proton
At which location will the electric field between the tow parallel plates of a charged capacitor be the strongest in magnitude?
midway between the two plates, nearest their center
The unit of capacitance, the farad, is dimmensionally equivalent to which of the following?
C/V
Increasing the voltage across the two plates of a capacitor will produce what effect on the capacitor?
Decrease capacitance
If two parallel, conducting plates have equal positive charge, the electric field lines will:
leave both plates and go to infinity
Increasing the separation of the two charged parallel plates of a capacitor, which are disconnected from a battery will produce what effect on the capacitor?
decrease capacitance
Inserting a dielectric material between two charged parallel conducting plates, originally separated by air and disconnected from a battery will produce what effect on the capacitor?
increase capacitance
If the current in a wire is tripled, what effect does this have on the electron drift velocity in the wire?
It triples
The size of the electric current in an electrical conductor is a function of which of the following?
All of the above choices are valid
When an electric current exists within a conducting wire, which of the following statements describes the condition of any accompanying electric field?
Must be parallel to current flow
Materials having resistance changes as voltage or current varies are called
Nonohmic
The unit of electric current, the ampere, is equivalent to which of the following?
V/Ohm
The unit of electric resistance, the ohm, is equivalent to which of the following?
V/A
If a certain resistor obeys Ohm’s law, its resistance will change
None of the above, since resistance is a constant for the given resistor
The quantity volt is equivalent to which of the following?
J/C
The unit for rate of energy transformation the watt in an electric circuit is equivalent to which of the following
VxA
Which is a unit of power?
J/s
Which is not a force?
Voltage
A light bulb with a tungsten filament is attached to a source of variable voltage. As the voltage is increased on the bulb,
The bulb’s resistance increases
The basic function of an electromotive force in a circuit is to do which of the following?
Convert some other form of energy into electrical
Which voltage is not caused by a source of emf?
The voltage across a charged capacitor
Three resistors with values of R1, R2, and R3, respectively are connected in series. Which of the following expresses the total resistance, RT, of the three resistors?
Rt= R1+ R2+ R3
Three resistors, each with resistance R1, are in series in a circuit. They are replaced by one equivalent resistor, R. Comparing this resistor to the first resistor of the initial circuit, which of the following is true?
The current through R equals the current through R1
When a light bulb is turned on, its resistance increases until it reaches operating temperature. What happens to the current in the bulb as it is warming up?
It decreases
Three resistors, each with resistance R1, are in parallel in a circuit. They are replaced by one equivalent resistor, R. Compare this resistor to the first resistor of the initial circuit. Which of the following statements is true?
The voltage across R equals the voltage across R1
If R1
R1
Household circuits are wired in
Parallel
In applications where electrical shocks may be more likely, such as around water in kitchens and bathrooms, special outlets called GFI’s are used. What does GFI stand for?
Ground fault interrupter
Houshold 120 V outlets are made to accept three pronged plugs. One of the prongs attaches to the “live” wire at 120 V, and another attaches to the “neutral” wire that is connected to ground. What is the third prong for?
It connects the case of the appliance directly to ground for safety procedures
Electrical charges and magnetic poles have many similarities, but one difference is:
A magnetic pole cannot be isolated
Which of the following is not a hard magnetic material?
Iron
Geophysicists today generally attribute the existence of the Earth’s magnetic field to which of the following?
Convection currents within the liquid interior
The term magnetic declination refers to which of the following?
Angle between directions to true north and magnetic north
The magnetic field of the Earth is believed responsible for which of the following?
deflection of charged cosmic rays
The magnetic pole of the Earth nearest the geographic North Pole corresponds to which of the following?
a magnetic south pole
The force on a charged particle created by its motion in a magnetic field is maximum at what angle between the particle and the velocity field?
90 degrees
Assume that a uniform magnetic field is directed into this page. If an electron is released with an initial velocity directed from the bottom edge to the top edge of the page, which of the following describes the direction of the resultant force acting on the electron?
to the right
A proton moves across the Earth’s equator in a northeasterly direction. At this point the Earth’s magnetic field has a direction due north and is parallel to the surface. What is the direction of the force acting on the proton at this instant?
out of the Earth’s surface
Different units can be used to measure the same physical quantity differing only by some multiplicative factor. The cgs unit for magnetic field the gauss is equal to ____ tesla
10^-4
If a proton is released at the equator and falls toward the Earth under the influence of gravity, the magnetic force on the proton will be toward the
east
A stationary positive charge +Q is located in a magnetic field B, which is directed toward the right as indicated. The direction of the magnetic force on Q is
There is no magnetic force
There is a magnetic field on a particle. It is possible that the particle is:
Not part of a wire
Which of the following devices makes use of an electromagnet?
Loudspeaker and Galvanometer
The direction of the force on a current carrying wire located in an external magnetic field is which of the following?
Perpindicular to the current
Parallel to the wire
A circular current loop is placed in an external magnetic field. How is the torque related to the radius of the loop?
Directly proportional to radius squared
Magnetism had been a known phenomenon for some time before its relation to electric currents was found. That a current in a wire produces a magnetic field was discovered by:
Oersted
A current in a long straight wire produces a magnetic field. The magnetic field lines:
Form circles that go around the wire
Two parallel wires are separated by 0.25 m. Wire A carries 5.0A and Wire B carries 10 A, both currents in the same direction. The force on .80m of Wire A is
Toward Wire B
A current in a solenoid coil creates a magnetic field inside that coil. The field strength is directly proportional to
The current
A current in a coil with N turns creates a magnetic field at the center of that loop. The field strength is directly proportional to:
Number of turns in the loop
Current strength
The magnetic domains in a non-magnetized piece of iron are characterized by which orientation?
Random
When an electromagnet has an iron core inserted, what happens to the strength of the magnet?
It increases
The units Tm^2/s are equivalent to
v
A sensitive ammeter is connected to a wire loop and placed within the magnetic field of a strong horseshoe magnet. The ammeter shows a deflection when
The wire is moved perpendicularly to the field
According to Lenz’s law the direction of an induced current in a conductor will be that which tends to produce which of the following effeects?
Oppose the effect which produces it
“GFI” stands for
Ground fault interrupter
The principle or law that says “an induced emf in a circuit loop produces a current whose magnetic field opposes further change of magnetic flux” is credited to:
Lenz
A coil is placed in a changing magnetic field and an emf is induced. What happens to the induced emf if the rate of change of magnetic field quadruples?
The emf quadruples
The magnet moving past an object will produce eddy currents in the object if the object
Is a conductor
The operation of a tape player to play music depends on which of the following?
Induced current from the motion of a magnet past a wire
If the induced current in a wire loop were such that the flux it produces were in the same direction as the change in external flux causing the current, which of the following conservation laws would end up being violated
Energy
The operation of an eleectric motor depends on which of the following effects??
The force acting on a current carrying wire in a magnetic field
The basic function of the electric generator is which of the following conversion processes?
Mechanical energy to electrical
The function of the electric motor is which one of the following conversion processes?
Electrical energy to mechanical
The back emf in an electric motor is its maximum value under which condition?
Motor speed is a maximum
Electricity may be generated by rotating a loop of wire between the poles of a magnet. The induced current is greatest when
The plane of the loop is parallel to the magnetic field
The “back emf” of a motor refers to a source of voltage that:
Is biggest when the motor turns fastest
When a voltage is generated by rotating a coil in a magnetic field at a constant rate, the period of the voltage equals the time that is takes for the coil to rotate through ____ radians
2pi
The self inductance of a solenoid increases under which of the following conditions
Only the number of coils is increased
By what factor is the self-inductance of an air solenoid changed if only its cross sectional area, A, is triple?
3
An inductor battery resistance and ammeter and switch are connected in series. If the switch, initially open, is not closed, what is the current’s final value?
battery voltage divided by resistance
In a circuit made up of inductor, resistance, ammeter, battery, and switch in series, at which of the following times after the switch is closed is the rate of current increase greatest?
zero
How is the energy stored in a current-carrying inductor related to its self inductance, L?
directly proportional to L
How is the energy stored in a current carrying inductor related to the current value, I?
directly proportional to I^2
Two equal charges, each Q, are separated by some distance. What third charge would need to be placed half way between the two charges so that the net force on each charge would be zero?
-Q/4
Q1 has 50 electric field lines radiating outward and Q2 has 100 field lines converging inward. What is the ration Q1/Q2?
-1/2
A spherical surface surrounds a point charge is its center. If the charge is doubled and if the radius of the surface is also doubled, what happens to the electric flux out of the surface and the magnitude E of the electric field at the surface as a result of these doublings?
Phi increases and E decreases
A wire has resistance R. A second wire has twice the length twice the diameter and twice the resistivity of the first wire. What is its resistance?
R
A coil is placed in a magnetic field and has a flux through it. The coil is stressed so that its area reduces to 75% of its original value. if the plane of the coil stays the same and the flux through it remains the same, how must the magnetic field change?
It must increase by 25%
The rate of heat dissipation in an AC circuit with resistance R and effective current I rms, is given by which of the following?
(Irms)^2R
There is a current I flowing in a clockwise direction in a square loop of wire that is in the plane of the paper. If the magnetic field is toward the right, and if each side of the loop has length L, then the net magnetic force acting on the loop is
ILB
Two parallel conductors are carrying currents in the opposite direction. The currents are non-zero and not necessarily equal. The magnitude of the magnetic field midway between them is 40 micro T. If one of the currents then has its direction reversed, what is the resulting magnitude of the magnetic field midway between them?
A value less than 40 microT
The frequency in an AC series circuit is doubled. By what factor does this change the capacitave reactance?
1/2
Two loops of wire are arranged so that a changing current in one, the primary, will induce a current in the other, the secondary. The secondary loop has twice as many turns as the primary loop. As long as the current in the primary is steady at 3 A, the current in the secondary will be
Zero
In an RLC series circuit if the AC frequency is increased to a very large value, what value does the phase angle between the current and voltage approach?
90 degrees
A bar magnet is held above the center of a conducting ring in the horizonal plane. The magnet is dropped so it falls lengthwise toward the center of the ring. Will the falling magnet be attracted toward the ring or be repelled by the ring due to the magnetic interaction of the magnet and the ring?
It will be repelled
In an AC series circuit, the current in a pure resistor differs in phase with the applied voltage by what angle?
Zero
The rms current is equal to the direct current that
dissipates an equal amount of energy in a resistor at the same rate as in an AC circuit
In a capacitor in an AC circuit, the voltage
lags by the current by 90 degrees
In an AC series circuit the voltage in the inductor differs in phase with the voltage in the capacitor by what angle
180 degrees
Consider an AC series circuit containing a coil capacitor and resistance. Tripling the frequency will change the inductive reactance by what factor
3.0
Consider an AC series circuit containing a coil, capacitor, and resistance. Tripling the frequency will change the capacitive reactance by what factor
1/3
Consider an AC series circuit containing a coil, capacitor, and resistance. Tripling the frequency will change the circuit’s impedance by what factor?
1113151634354952
information is insufficient to determine answer
Resonance occurs in an AC series circuit when which of the following conditions is met?
capacitive reactance equals inductive reactance
An ideal transformer is one that
experiences no power loss
An electromagnetic wave is made up of which of the following oscillating quantities
magnetic fields only
In an RLC circuit, the maximum current is 1 amp. What is the average current?
(1/2)A
An RLC circuit has resistance Rnought, inductance Lnought, and capacitance Cnought. If the resistance value is now doubled, which values of inductance and capacitance will result in the same resonant frequency as before
2Lnough, Cnought/2
A series circuit has equal values for resistance, capacitive reactance, and inductive reactance. The phase angle for this circuit is
not given
The power factor in an AC series circuit is equal to which of the following ratios?
resistance to impedences
A series RLC circuit in a radio is in resonance with AM 600 kHz. If the radio station is changed to AM 1 200 kHz by what factor must the capacitance be multiplied to again achieve resonance
1/4
When an RLC series circuit is in resonance, its impedance is
equal to its resistance
A series RLC cicuit has a inductive reactance of 4 ohms and a capacitive reactance of 1/4 ohms. By what factor should the AC frequency be changed to put this circuit into resonance
1/4
