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95問 • 2年前

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A charged particle is placed in an electric field that varies with location. No force is exerted on this charge: A. at locations where the electric field is zero B. at locations where the electric field strength is 1/(1.6 × 10-19)N/C C. if the particle is moving along a field line D. if the particle is moving perpendicularly to a field line E. if the field is caused by an equal amount of positive and negative charge

An electron traveling north enters a region where the electric field is uniform and points north The electron: A. speeds up B. slows down C. veers east D. veers west E. continues with the same speed in the same direction

An electron traveling north enters a region where the electric field is uniform and points west. The electron: A. speeds up B. slows down C. veers east D. veers west E. continues with the same speed in the same direction

An electric dipole consists of a particle with a charge of +6 × 10-6 Cat the origin and a particle with a charge of -6 x 10- C on the r axis at ~ = 3 x 10- m. Its dipole moment is: A. 1.8 x 10-$ C - m, in the positive a direction B. 1.8 x 10-$ C - m, in the negative z direction C. 0 because the net charge is 0 D. 1.8 x 10-8 C- m, in the positive y direction E. 1.8 x 10-8 C m, in the negative y direction

The force exerted by a uniform electric field on a dipole is: A. parallel to the dipole moment B. perpendicular to the dipole moment C. parallel to the electric field D. perpendicular to the electric field E. none of the above

An electric field exerts a torque on a dipole only if: A. the field is parallel to the dipole moment B. the field is not parallel to the dipole moment C. the field is perpendicular to the dipole moment D. the field is not perpendicular to the dipole moment E. the field is uniform

The torque exerted by an electric field on a dipole is: A. parallel to the field and perpendicular to the dipole moment B. parallel to both the field and dipole moment C. perpendicular to both the field and dipole moment D. parallel to the dipole moment and perpendicular to the field E. not related to the directions of the field and dipole moment

When the dipole moment of a dipole in a uniform electric field rotates to become more nearly aligned with the field: A. the field does positive work and the potential energy increases B. the field does positive work and the potential energy decreases C. the field does negative work and the potential energy increases D. the field does negative work and the potential energy decreases E. the field does no work

The purpose of Milliken's oil drop experiment was to determine: A. the mass of an electron B. the charge of an electron C. the ratio of charge to mass for an electron D. the sign of the charge on an electron E. viscosity

Consider Gauss's law: fE-d^ = q/co. Which of the following is true? A. E must be the electric field due to the enclosed charge B. If g = 0, then E = 0 everywhere on the Gaussian surface C. If the three particles inside have charges of +q, +q, and -2q, then the integral is zero D. on the surface E is everywhere parallel to dA E. If a charge is placed outside the surface, then it cannot affect E at any point on the surface

A charged point particle is placed at the center of a spherical Gaussian surface. The electric flux ®E is changed if: A. the sphere is replaced by a cube of the same volume B. the sphere is replaced by a cube of one-tenth the volume C. the point charge is moved off center (but still inside the original sphere) D. the point charge is moved to just outside the sphere E. a second point charge is placed just outside the sphere

Choose the INCORRECT statement: A. Gauss' law can be derived from Coulomb's law B. Gauss' law states that the net number of lines crossing any closed surface in an outward direction is proportional to the net charge enclosed within the surface C. Coulomb's law can be derived from Gauss' law and symmetry D. Gauss' law applies to a closed surface of any shape E. According to Gauss' law, if a closed surface encloses no charge, then the electric field must vanish everywhere on the surface

The outer surface of the cardboard center of a paper towel roll: A. is a possible Gaussian surface B. cannot be a Gaussian surface because it encloses no charge C. cannot be a Gaussian surface since it is an insulator D. cannot be a Gaussian surface because it is not a closed surface

A particle with charge Q is placed outside a large neutral conducting sheet. At any point in the interior of the sheet the electric field produced by charges on the surface is directed: A. toward the surface B. away from the surface C. toward Q D. away from Q

A hollow conductor is positively charged. A small uncharged metal ball is lowered by a silk thread through a small opening in the top of the conductor and allowed to touch its inner surface. After the ball is removed, it will have: A. a positive charge B. a negative charge C. no appreciable charge D. a charge whose sign depends on what part of the inner surface it touched E. a charge whose sign depends on where the small hole is located in the conductor

Two conducting spheres are far apart. The smaller sphere carries a total charge Q. The larger sphere has a radius that is twice that of the smaller and is neutral. After the two spheres are connected by a conducting wire, the charges on the smaller and larger spheres, respectively, A. Q/2 and Q/2 B. Q/3 and 2Q/3 C. 2Q/3 and Q/3 D. zero and Q E. 2Q and -Q

A conducting sphere with radius R is charged until the magnitude of the electric field just outside its surface is E. The electric potential of the sphere, relative to the potential far away, is: A.zero B. E/R C. E/R? D. ER E. ER?

In a certain region of space the electric potential increases uniformly from east to west and does not vary in any other direction. The electric field: A. points east and varies with position B. points east and does not vary with position C. points west and varies with position D. points west and does not vary with position B. points north and does not vary with position

The electric field in a region around the origin is given by E = C(ai + y), where C is a constant. The equipotential surfaces in that region are: A. concentric cylinders with axes along the z axis B. concentric cylinders with axes along the ~ axis C. concentric spheres centered at the origin D. planes parallel to the zy plane E. planes parallel to the y plane

The electric potential in a certain region of space is given by V = -7.5 x^2 + 3z, where V is in volts and ~ is in meters. In this region the equipotential surfaces are: A. planes parallel to the a axis B. planes parallel to the y plane C. concentric spheres centered at the origin D. concentric cylinders with the axis as the cylinder axis D. unknown unless the charge is given

A particle with charge q is to be brought from far away to a point near an electric dipole. No work is done if the final position of the particle is on: A. the line through the charges of the dipole B. a line that is perpendicular to the dipole moment C. a line that makes an angle of 45° with the dipole moment D. a line that makes an angle of 30° with the dipole moment E. none of the above

Equipotential surfaces associated with an electric dipole are: A. spheres centered on the dipole B. cylinders with axes along the dipole moment C. planes perpendicular to the dipole moment D. planes parallel to the dipole moment E. none of the above

The units of capacitance are equivalent to: A. J/C B. V/C C. J2/C D. C/J E. C2/J

A farad is the same as a: A. J/V B. V/J C. C/V D. V/C E. N/C

A capacitor C "has a charge Q. The actual charges on its plates are: A. Q, Q B. Q/2, Q/2 C. Q, -Q D. Q/2, -0/2 E. Q, 0

The capacitance of a parallel-plate capacitor is: A. proportional to the plate area B. proportional to the charge stored C. independent of any material inserted between the plates D. proportional to the potential difference of the plates E. proportional to the plate separation

The capacitance of a parallel-plate capacitor can be increased by: A. increasing the charge B. decreasing the charge C. increasing the plate separation D. decreasing the plate separation E. decreasing the plate area

If both the plate area and the plate separation of a parallel-plate capacitor are doubled, the capacitance is: A. doubled B. halved C. unchanged D. tripled E. quadrupled

If the plate area of an isolated charged parallel-plate capacitor is doubled: A. the electric field is doubled B. the potential difference is halved C. the charge on each plate is halved D. the surface charge density on each plate is doubled E. none of the above

If the plate separation of an isolated charged parallel-plate capacitor is doubled: A. the electric field is doubled B. the potential difference is halved C. the charge on each plate is halved D. the surface charge density on each plate is doubled E. none of the above

Pulling the plates of an isolated charged capacitor apart: A. increases the capacitance B. increases the potential difference C. does not affect the potential difference D. decreases the potential difterence B. does not affect the capacitance

If the charge on a parallel-plate capacitor is doubled: A. the capacitance is halved B. the capacitance is doubled C. the electric field is halved D. the electric field is doubled E. the surface charge density is not changed on either plate

The capacitance of a cylindrical capacitor can be increased by: A. decreasing both the radius of the inner cylinder and the length B. increasing both the radius of the inner cylinder and the length C. increasing the radius of the outer cylindrical shell and decreasing the length D. decreasing the radius of the inner cylinder and increasing the radius of the outer cylindrical shell E. only by decreasing the length

A battery is used to charge a series combination of two identical capacitors. If the potential difference across the battery terminals is V and total charge Q flows through the battery during the charging process then the charge on the positive plate of each capacitor and the potential difference across each capacitor are: A. Q/2 and V/2, respectively B. Q and V, respectively C. Q/2 and V, respectively D. Q and V/2, respectively E. Q and 2V, respectively

A battery is used to charge a parallel combination of two identical capacitors. If the potential difference across the battery terminals is V and total charge Q flows through the battery during the charging process then the charge on the positive plate of each capacitor and the potential difference across each capacitor are: A. Q/2 and V/2, respectively B. Q and V, respectively C. Q/2 and V, respectively D. Q and V/2, respectively E. Q and 2V, respectively

A 2- F and a 1- F capacitor are connected in series and a potential difference is applied across the combination. The 2-F capacitor has: A. twice the charge of the 1-pF capacitor B. half the charge of the 1-F capacitor C. twice the potential difference of the 1-F capacitor D. half the potential difference of the 1-F capacitor E. none of the above

A 2- F and a 1- F capacitor are connected in parallel and a potential difference is applied across the combination. The 2-pF capacitor has: A. twice the charge of the 1-F capacitor B. half the charge of the 1-pF capacitor C. twice the potential difference of the 1-pF capacitor D. half the potential difference of the 1-F capacitor E. none of the above

Let Q denote charge, V denote potential difference, and U denote stored energy. Of these quantities. capacitors in series must have the same: A. Q only B. V only C. U only D. Q and U only E. V and U only

Let Q denote charge, V denote potential difference, and U denote stored energy. Of these quantities, capacitors in parallel must have the same: A. Q only B. V only C. U only D. Q and U only E. V and U only

Capacitors C1 and C2 are connected in series and a potential difference is applied to the combination. If the capacitor that is equivalent to the combination has the same potential difference, then the charge on the equivalent capacitor is the same as: A. the charge on C B. the sum of the charges on C1 and C2 C. the difference of the charges on C1 and C2 D. the product of the charges on C, and Cz E. none of the above

Capacitors C and C2 are connected in parallel and a potential difference is applied to the combination. If the capacitor that is equivalent to the combination has the same potential difference, then the charge on the equivalent capacitor is the same as: A. the charge on C B. the sum of the charges on C1 and C2 C. the difference of the charges on C1 and C2 D. the product of the charges on C, and Cz E. none of the above

Two identical capacitors are connected in series and two, each identical to the first, are connected in parallel. The equivalent capacitance of the series connection is the equivalent capacitance of parallel connection. A. twice B. four times C. half D. one-fourth E. the same as

Two identical capacitors, each with capacitance C, are connected in parallel and the combination is connected in series to a third identical capacitor. The equivalent capacitance of this A. 2C/3 B. C C. 3C/2 D. 2C E. 3C

A 2-F and a 1-pF capacitor are connected in series and charged from a battery. They store charges P and Q, respectively. When disconnected and charged separately using the same battery, they have charges R and S, respectively. Then: A. R>S > Q=P B. P>Q>R=S C. R>P=0> S D. R = P>S=Q E. R>P>S= Q

A 2- F and a 1- F capacitor are connected in series and charged by a battery. They store energies P and Q, respectively. When disconnected and charged separately using the same battery, they store energies R and S, respectively. Then: A. R>P>S >0 B. P>Q>R>S C. R>P>Q>S D. P>R>S >Q E. R>S >Q> P

The quantity (1/2)€o E° has the significance of: A. energy/farad B. energy/coulomb C. energy D. energy/volume E. energy/volt

A battery is used to charge a parallel-plate capacitor, after which it is disconnected. Then the plates are pulled apart to twice their original separation. This process will double the: A. capacitance B. surface charge density on each plate C. stored energy D. electric field between the two places E. charge on each plate

A dielectric slab is slowly inserted between the plates of a parallel plate capacitor, while the potential difference between the plates is held constant by a battery. As it is being inserted: A. the capacitance, the potential difference between the plates, and the charge on the positive plate all increase B. the capacitance, the potential difference between the plates, and the charge on the positive plate all decrease C. the potential difference between the plates increases, the charge on the positive plate de-creases, and the capacitance remains the same D. the capacitance and the charge on the positive plate decrease but the potential difference between the plates remains the same E. the capacitance and the charge on the positive plate increase but the potential difference between the plates remains the same

One of materials listed below is to be placed between two identical metal sheets, with no, air gap, to form a parallel-plate capacitor. Which produces the greatest capacitance? A. material of thickness 0.1 mm and dielectric constant 2 B. material of thickness 0.2 mm and dielectric constant 3 C. material of thickness 0.3 mm and dielectric constant 2 D. material of thickness 0.4mm and dielectric constant 8 E. material of thickness 0.5 mm and dielectric constant 11

Two capacitors are identical except that one is filled with air and the other with oil. Both capacitors carry the same charge. The ratio of the electric fields Ear/ Eoil is: A. between 0 and 1 B. 1 C. between 1 and infinity D. infinite

A parallel-plate capacitor, with air dielectric, is charged by a battery, after which the battery is disconnected. A slab of glass dielectric is then slowly inserted between the plates. As it is being inserted: A. a force repels the glass out of the capacitor B. a force attracts the glass into the capacitor C. no force acts on the glass D. a net charge appears on the glass E. the glass makes the plates repel each other

Two parallel-plate capacitors with the same plate separation but different capacitance are connected in parallel to a battery. Both capacitors are filled with air. The quantity that is NOT the same for both capacitors when they are fully charged is: A. potential difference B. energy density C. electric field between the plates D. charge on the positive plate E. dielectric constant

Two parallel-plate capacitors with the same plate area but different capacitance are connected in parallel to a battery. Both capacitors are filled with air. The quantity that is the same for both capacitors when they are fully charged is: A. potential difference B. energy density C. electric field between the plates D. charge on the positive plate E. plate separation

Two parallel-plate capacitors with different plate separation but the same capacitance are connected in series to a battery. Both capacitors are filled with air. The quantity that is NOT the same for both capacitors when they are fully charged is: A. potential difference B. stored energy C. electric field between the plates D. charge on the positive plate E. dielectric constant

Two parallel-plate capacitors with different capacitance but the same plate separation are connected in series to a battery. Both capacitors are filled with air. The quantity that is the same for both capacitors when they are fully charged is: A. potential difference B. stored energy C. energy density D. electric field between the plates E. charge on the positive plate

Current has units: A. kilowatt-hour B. coulomb/second C. coulomb D. volt E. Ohm

Current is a measure of: A. force that moves a charge past a point B. resistance to the movement of a charge past a point C. energy used to move a charge past a point D. amount of charge that moves past a point per unit time E. speed with which a charge moves past a point

Conduction electrons move to the right in a certain wire. This indicates that: A. the current density and electric field both point right B. the current density and electric field both point left C. the current density points right and the electric field points left D. the current density points left and the electric field points right E. the current density points left but the direction of the electric field is unknown

Two wires made of different materials have the same uniform current density. They carry the same current only if: A. their lengths are the same B. their cross-sectional areas are the same C. both their lengths and cross-sectional areas are the same D. the potential differences across them are the same E. the electric fields in them are the same

In a conductor carrying a current we expect the electron drift speed to be: A. much greater than the average electron speed B. much less than the average electron speed C. about the same as the average electron speed D. less than the average electron speed at low temperature and greater than the average electron speed at high temperature E. less than the average electron speed at high temperature and greater than the average electron speed at low temperature

Two substances are identical except that the electron mean free time for substance A is twice the electron mean free time for substance B. If the same electric field exists in both substances the electron drift speed in A is: A. the same as in B B. twice that in B C. half that in B D. four times that in B E. one-fourth that in B

The current is zero in a conductor when no potential difference is applied because: A. the electrons are not moving B. the electrons are not moving fast enough C. for every electron with a given velocity there is another with a velocity of equal magnitude and opposite direction. D. equal numbers of electrons and protons are moving together E. otherwise Ohm's law would not be valid

If J is the eurrent density and dA is a vector element of area then the integral ( J- dA over an area represents: A. the electric flux through the area B. the average current density at the position of the area C. the resistance of the area D. the resistivity of the area E. the current through the area

If the potential difference across a resistor is doubled: A. only the current is doubled B. only the current is halved C. only the resistance is doubled D. only the resistance is halved E. both the current and resistance are doubled

Of the following, the copper conductor that has the least resistance is: A. thin, long and hot B. thick, short and cool C. thick, long and hot D. thin, short and cool E. thin, short and hot

The resistance of a rod does NOT depend on: A. its temperature B. its material C. its length D. its conductivity E. the shape of its (fixed) cross-sectional area

Two wires are made of the same material and have the same length but different radii. They are joined end-to-end and a potential difference is maintained across the combination. Of the following the quantity that is the same for both wires is: A. potential difference B. current C. current density D. electric field E. conduction electron drift speed

For an ohmic substance the resistivity is the proportionality constant for: A. current and potential difference B. current and electric field C. current density and potential difference D. current density and electric field E. potential difference and electric field

For an ohmic resistor, resistance is the proportionality constant for: A. potential difference and electric field B. current and electric field C. current and length D. current and cross-sectional area E. current and potential terence

For an ohmic substance, the resistivity depends on: A. the electric field B. the potential difference C. the current density D. the electron mean free time E. the cross-sectional area of the sample

For a cylindrical resistor made of ohmic material, the resistance does NOT depend on: A. the current B. the length C. the cross-sectional area D. the resistivity E. the electron drift velocity

For an ohmic substance, the electron drift velocity is proportional to: A. the cross-sectional area of the sample B. the length of the sample C. the mass of an electron D. the electric field in the sample E. none of the above

You wish to triple the rate of energy dissipation in a heating device. To do this you could triple: A. the potential difference keeping the resistance the same B. the current keeping the resistance the same C. the resistance keeping the potential difference the same D. the resistance keeping the current the same E. both the potential difference and current

It is better to send 10, 000 kW of electric power long distances at 10, 000 V rather than at 220 V because: A. there is less heating in the transmission wires B. the resistance of the wires is less at high voltages C. more current is transmitted at high voltages D. the insulation is more effective at high voltages E. the iR drop along the wires is greater at high voltage

You buy a «75 W" light bulb. The label means that: A. no matter how you use the bulb, the power will be 75 W B. the bulb was filled with 75 W at the factory C. the actual power dissipated will be much higher than 75 W since most of the power appears as heat D. the bulb is expected to burn out after you use up its 75 W E. none of the above

"The sum of the currents into a junction equals the sum of the currents out of the junction" a consecquence of: A. Newton's third law B. Ohm's law C. Newton's second law D. conservation of energy E. conservation of charge

"The sum of the emf's and potential differences around a closed loop equals zero" is a consequence of: A. Newton's third law B. Ohm's law C. Newton's second law D. conservation of energy E. conservation of charge

In the context of the loop and junctions rules for electrical circuits a junction is: A. where a wire is connected to a resistor B. where a wire is connected to a battery C. where only two wires are joined D. where three or more wires are joined E. where a wire is bent

For any circuit the number of independent equations containing emf's, resistances, and currents equals: A. the number of junctions B. the number of junctions minus 1 C. the number of branches D. the number of branches minus 1 E. the number of closed loops

A battery is connected across a series combination of two identical resistors. If the potential difference across the terminals is V and the current in the battery is i, then: A. the potential difference across each resistor is V and the current in each resistor is i B. the potential difference across each resistor is V/2 and the current in each resistor is i/2 C. the potential difference across each resistor is V and the current in each resistor is i/2 D. the potential difference across each resistor is V/2 and the current in each resistor is i

A battery is connected across a parallel combination of two identical resistors. If the potential difference across the terminals is V and the current in the battery is i, then: A. the potential difference across each resistor is V and the current in each resistor is i B. the potential difference across each resistor is V/2 and the current in each resistor is i/2 C. the potential difference across each resistor is V and the current in each resistor is i/2 D. the potential difference across each resistor is V/2 and the current in each resistor is i

Two wires made of the same material have the same lengths but different diameters. They are connected in parallel to a battery. The quantity that is NOT the same for the wires is: A. the end-to-end potential difference B. the current C. the current density D. the electric field E. the electron drift velocity

Two wires made of the same material have the same lengths but different diameters. They are connected in series to a battery. The quantity that is the same for the wires is: A. the end-to-end potential difference B. the current C. the current density D. the electric field E. the electron drift velocity

The emt of a battery is equal to its terminal potential difference: A. under all conditions B. only when the battery is being charged C. only when a large current is in the battery D. only when there is no current in the battery E. under no conditions

The terminal potential difference of a battery is less than its emf: A. under all conditions B. only when the battery is being charged C. only when the battery is being discharged D. only when there is no current in the battery E. under no conditions

A series circuit consists of a battery with internal resistance r and an external resistor R. If these two resistances are equal (r = R) then the thermal energy generated per unit time by the internal resistance r is: A. the same as by R B. half that by R C. twice that by R D. one-third that by R E. unknown unless the emf is given

To make a galvanometer into an ammeter, connect: A. a high resistance in parallel B. a high resistance in series C. a low resistance in series D. a low resistance in parallel

An initially uncharged capacitor C is connected in series with resistor R. This combination is then connected to a battery of emf V. Sufficient time elapses so that a steady state is reached. Which of the following statements is NOT true? A. The time constant is independent of V B. The final charge on C is independent of R C. The total thermal energy generated by R. is independent of R D. The total thermal energy generated by R is independent of V E. The initial current (just after the battery was connected) is independent of C

In the capacitor discharge formula q = goe-t/RC the symbol t represents: A. the time constant B. the time it takes for C to lose the fraction 1/e of its initial charge C. the time it takes for C to lose the fraction (1 - 1/e) of its initial charge D. the time it takes for C to lose essentially all of its initial charge E. none of the above

In the formula F = qü× B: A. F must be perpendicular to © but not necessarily to B B. F must be perpendicular to B but not necessarily to u C.  must be perpendicular to B but not necessarily to F D. all three vectors must be mutually perpendicular E. F must be perpendicular to both ‹ and B

At any point the magnetic field lines are in the direction of: A. the magnetic force on a moving positive charge B. the magnetic force on a moving negative charge C. the velocity of a moving positive charge D. the velocity of a moving negative charge E. none of the above

Lines of the magnetic field produced by a long straight wire carrying a current are

circles that are concentric with the wire

In an overhead straight wire, the current is north. The magnetic field due to this current, at our point of observation,

west

A wire carrying a large current i from east to west is placed over an ordinary magnetic compass. The end of the compass needle marked "N" will point: A. north B. sonth C. east D. west

south

The reservoir of a hydroelectric generating station measures 217.8 ft by 200 ft at the surface. Its head decreases by 1ft while the station generates 100 hp at 70 percent efficiency. Find the original head in feet.

104

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