Q&A Hero

Q: A 3.5 mH inductor and a 4.5 mH inductor are connected in series and a time varying current is established in them. When the total emf of the combination is 16 V, the emf of the larger inductor is: A) 2.3 V B) 7.0 V C) 9.0 V D) 28 V E) 36 V

Q: A 3.5 mH inductor and a 4.5 mH inductor are connected in series. The equivalent inductance is: A) 0.13 mH B) 0.51 mH C) 1.0 mH D) 2.0 mH E) 8.0 mH

Q: A 10-turn ideal solenoid has an inductance of 4.0 mH. To generate an emf of 2.0 V the current should change at a rate of: A) 0 A/s B) 0.5 A/s C) 50 A/s D) 250 A/s E) 500 A/s

Q: A flat coil of wire, having 5 turns, has an inductance L. The inductance of a similar coil having 20 turns is: A) 4L B) L/4 C) 16L D) L/16 E) L

Q: A long narrow solenoid has length and a total of Nturns, each of which has cross-sectional area A. Its inductance is:

Q: A 10-turn ideal solenoid has an inductance of 3.5 mH. When the solenoid carries a current of 2.0 A the magnetic flux through each turn is:A) 0 WbB) 3.5 x10-4WbC) 7.0 x10-4WbD) 7.0 x10-3WbE) 7.0 x10-2Wb

Q: The unit "henry" is equivalent to:A) volt.second/ampereB) volt/secondC) ohmD) ampere.volt/secondE) ampere.second/volt

Q: A cylindrical region of radius Rcontains a uniform magnetic field, parallel to its axis, with magnitude that is changing linearly with time. If ris the radial distance from the cylinder axis, the magnitude of the induced electric field outside the cylinder is proportional to: A) R B) r C) r2 D) 1/r E) 1/r2

Q: A cylindrical region of radius Rcontains a uniform magnetic field, parallel to its axis, with magnitude that is changing linearly with time. If ris the radial distance from the cylinder axis, the magnitude of the induced electric field inside the cylindrical region is proportional to: A) R B) r C) r2 D) 1/r E) 1/r2

Q: A cylindrical region of radius Rcontains a uniform magnetic field parallel to its axis. The field is zero outside the cylinder. If the magnitude of the field is changing at the rate dB/dt, the electric field induced at a point 2Rfrom the cylinder axis is: A) 0 B) 2R dB/dt C) R dB/dt D) (R/2)dB/dt E) (R/4)dB/dt

Q: A cylindrical region of radius R= 3.0 cm contains a uniform magnetic field parallel to its axis. If the electric field induced at a point R/2 from the cylinder axis is 4.5 ï‚´10-3V/m the magnitude of the magnetic field must be changing at the rate of: A) 0 T/s B) 0.30 T/s C) 0.60 T/s D) 1.2 T/s E) 2.4 T/s

Q: An electric field is associated with every: A) magnetic field B) time-dependent magnetic field C) position-dependent magnetic field D) object moving in a magnetic field E) conductor moving in a magnetic field

Q: Which statement about eddy currents is false? A) They can be prevented by cutting a slot in a solid conducting plate, to prevent electrons from being able to make a complete circuit. B) The mechanical energy that is lost when eddy currents are created returns when the eddy currents cease. C) They can be used as a passive braking system, as no external power source is needed if permanent magnets are used. D) They are created in solid conducting plates as they move in and out of magnetic fields. E) The faster the conductor moves, the larger the eddy currents will be.

Q: As a loop of wire with a resistance of 10 moves in a non-uniform magnetic field, it loses kinetic energy at a uniform rate of 5 mJ/s. The induced emf in the loop is: A) 0 V B) 0.22 V C) 0.28 V D) 2.0 V E) cannot be calculated from the given data

Q: As a loop of wire with a resistance of 10 moves in a constant non-uniform magnetic field, it loses kinetic energy at a uniform rate of 5.0mJ/s. The induced current in the loop is:A) 0 AB) 2.0 mAC) 2.8 mAD) 22 mAE) cannot be calculated from the given data

Q: A rod of length Land electrical resistance Rmoves through a constant uniform magnetic field ;both the magnetic field and the direction of motion are parallel to the rod. The force that must be applied by a person to keep the rod moving with constant velocity is: A) 0 B) BLv C) BLv/R D) B2L2v/R E) B2L2v2/R

Q: A rod with resistance Rlies across frictionless conducting rails in a constant uniform magnetic field B, as shown. Assume the rails have negligible resistance. The magnitude of the force that must be applied by a person to pull the rod to the right at constant speed vis: A) 0 B) BLv C) BLv/R D) B2L2v/R E) B2Lxv/R

Q: A copper penny slides on a horizontal frictionless table. There is a square region of constant uniform magnetic field perpendicular to the table, as shown. Which graph correctly shows the speed vof the penny as a function of time t? A) I B) II C) III D) IV E) V

Q: The circuit shown is in a uniform magnetic field that is into the page. The current in the circuit is 0.20 A. At what rate is the magnitude of the magnetic field changing?Is it increasing or decreasing? A) 0 T/s B) 140 T/s, decreasing C) 140 T/s, increasing D) 420 T/s, decreasing E) 420 T/s, increasing

Q: At a particular instant of time the total magnetic flux through a stationary conducting loop is less in magnitude than the flux associated with an externally applied field. This might occur because: A) the applied field is normal to the loop and increasing in magnitude B) the applied field is normal to the loop and decreasing in magnitude C) the applied field is parallel to the plane of the loop and increasing in magnitude D) the applied field is parallel to the plane of the loop and decreasing in magnitude E) the applied field is tangent to the loop

Q: As an externally generated magnetic field through a certain conducting loop increases in magnitude, the field produced at points inside the loop by the current induced in the loop must be: A) increasing in magnitude B) decreasing in magnitude C) in the same direction as the applied field D) directed opposite to the applied field E) perpendicular to the applied field

Q: A square loop of wire moves with a constant speed vfrom a field-free region into a region of uniform Bfield, as shown. Which of the five graphs correctly shows the induced current iin the loop as a function of time t?A) IB) IIC) IIID) IVE) V

Q: The figure shows a bar moving to the right on two conducting rails. To make an induced current iin the direction indicated, a constant magnetic field between the rails should be in what direction?A) RightB) LeftC) Into the pageD) Out of the pageE) Impossible, cannot be done with a constant magnetic field

Q: A circular loop of wire is positioned half in and half out of a square region of constant uniform magnetic field directed into the page, as shown. To induce a clockwise current in this loop:A) move it in +xdirectionB) move it in +ydirectionC) move it in -xdirectionD) move it in -ydirectionE) increase the strength of the magnetic field

Q: A circular loop of wire rotates about a diameter in a magnetic field that is perpendicular to the axis of rotation. Looking in the direction of the field at the loop the induced current is: A) always clockwise B) always counterclockwise C) clockwise in the lower half of the loop and counterclockwise in the upper half D) clockwise in the upper half of the loop and counterclockwise in the lower half E) sometimes clockwise and sometimes counterclockwise

Q: A vertical bar magnet is dropped through the center of a horizontal loop of wire, with its north pole leading. At the instant when the midpoint of the magnet is in the plane of the loop, the induced current in the loop, viewed from above, is: A) maximum and clockwise B) maximum and counterclockwise C) not maximum but clockwise D) not maximum but counterclockwise E) essentially zero

Q: You push a permanent magnet with its north pole away from you toward a loop of conducting wire in front of you. Before the north pole enters the loop the current in the loop is: A) zero B) clockwise C) counterclockwise D) to your left E) to your right

Q: A rectangular loop of wire is placed midway between two long straight parallel conductors as shown. The conductors carry currents i1and i2as indicated. If i1is increasing and i2is constant, then the induced current in the loop is: A) zero B) clockwise C) counterclockwise D) depends on i1" i2 E) depends on i1+ i2

Q: A long straight wire is in the plane of a rectangular conducting loop. The straight wire initially carries a constant current iin the direction shown. While the current iis being shut off, the current in the loop is: A) zero B) clockwise C) counterclockwise D) clockwise in the left side and counterclockwise in the right side E) counterclockwise in the left side and clockwise in the right side

Q: A long straight wire is in the plane of a rectangular conducting loop. The straight wire carries an increasing current in the direction shown. The current in the loop is: A) zero B) clockwise C) counterclockwise D) clockwise in the left side and counterclockwise in the right side E) counterclockwise in the left side and clockwise in the right side

Q: A long straight wire is in the plane of a rectangular conducting loop. The straight wire carries a constant current i, as shown. While the wire is being moved toward the loop, the current in the loop is: A) zero B) clockwise C) counterclockwise D) clockwise in the left side and counterclockwise in the right side E) counterclockwise in the left side and clockwise in the right side

Q: A square loop of wire lies in the plane of the page. A decreasing magnetic field is directed into the page. The induced current in the loop is: A) counterclockwise B) clockwise C) zero D) up the left edge and from right to left along the top edge E) through the middle of the page

Q: A magnet moves inside a coil. Consider the following factors: I. strength of the magnet II. number of turns in the coil III. speed at which the magnet moves Which can affect the emf induced in the coil? A) I only B) II only C) III only D) I and II only E) I, II, III

Q: One hundred turns of insulated copper wire are wrapped around an iron core of cross-sectional area 0.100 m2. The circuit is completed by connecting the coil to a 10-resistor. As the magnetic field along the coil axis changes from 1.00 T in one direction to 1.00 T in the other direction, the total charge that flows through the resistor is:A) 0.01 CB) 0.02 CC) 0.2 CD) 1 CE) 2 C

Q: A merry-go-round has an area of 300 m2and spins at 2 rpm about a vertical axis at a place where the Earth's magnetic field is vertical and has a magnitude of 5 x10-5T. The emf around the rim is:A) 0 VB) 0.5 mVC) 3.1 mVD) 15 mVE) 190 mV

Q: A single loop of wire with a radius of 7.5 cm rotates about a diameter in a uniform magnetic field of 1.6 T. To produce a maximum emf of 1.0 V, it should rotate at: A) 0 rad/s B) 2.7 rad/s C) 5.6 rad/s D) 35 rad/s E) 71 rad/s

Q: The diagram shows a circular loop of wire that rotates at a steady rate about a diameter O that is perpendicular to a uniform magnetic field. The maximum induced emf occurs when the point X on the loop passes: A) a B) b C) c D) d E) e

Q: A 10 turn conducting loop with a radius of 3.0 cm spins at 60 revolutions per second in a magnetic field of 0.50 T. The maximum emf generated is: A) 0.014 V B) 0.085 V C) 0.53 V D) 0.85 V E) 5.3 V

Q: A copper hoop is held in a vertical east-west plane in a uniform magnetic field whose field lines run along the north-south direction. The largest induced emf is produced when the hoop is: A) rotated about a north-south axis B) rotated about an east-west axis C) moved rapidly, without rotation, toward the east D) moved rapidly, without rotation, toward the south E) moved rapidly, without rotation, toward the northwest

Q: A rectangular loop of wire is placed perpendicular to a uniform magnetic field and then spun around one of its sides at frequencyf.The induced emf is a maximum when: A) the flux is zero B) the flux is a maximum C) the flux is half its maximum value D) the derivative of the flux with respect to time is zero E) none of the above

Q: The four wire loops shown have edge lengths of either L, 2L, or 3L. They will move with the same speed into a region of uniform magnetic field directed out of the page. Rank them according to the maximum magnitude of the induced emf, least to greatest.A) 1 and 2 tie, then 3 and 4 tieB) 3 and 4 tie, then 1 and 2 tieC) 4, then 2 and 3 tie, then 1D) 1, then 2 and 3 tie, then 4E) 1, 2, 3, 4

Q: A changing magnetic field pierces the interior of a circuit containing three identical resistors. Two voltmeters are connected as shown. V1reads 1 mV across R. V2reads the voltage across the other two resistors, which is:A) 0 VB) 1/3 mVC) 1/2 mVD) 1 mVE) 2 mV

Q: The graph shows the magnitude Bof a uniform magnetic field that is perpendicular to the plane of a conducting loop. Rank the four regions indicated on the graph according to the magnitude of the emf induced in the loop, from least to greatest. A) 1, 2, 3, 4 B) 2, 4, 3, 1 C) 4, 3, 1, 2 D) 1, 3, 4, 2 E) 4, 3, 2, 1

Q: A rectangular loop of wire has area A. It is placed perpendicular to a uniform magnetic field Band then spun around one of its sides at frequencyf.The maximum induced emf is:

Q: A car travels northward at 75 km/h along a straight road in a region where Earth's magnetic field has a vertical component of 0.50 x10-4T. The emf induced between the left and right side, separated by 1.7 m, is:A) 0 VB) 1.8 mVC) 3.6 mVD) 6.4 mVE) 23 mV

Q: A rod lies across frictionless rails in a uniform magnetic field B, as shown. The rod moves to the right with speed v. In order for the emf around the circuit to be zero, the magnitude of the magnetic field should: A) not change B) increase linearly with time C) decrease linearly with time D) increase quadratically with time E) decrease quadratically with time

Q: Coils P and Q each have a large number of turns of insulated wire. When switch S is closed, the pointer of galvanometer G is deflected toward the left. Now that S is closed, to make the pointer of G deflect toward the right one could: A) move the slide of the rheostat R quickly to the right B) move coil P toward coil Q C) move coil Q toward coil P D) open S E) do none of the above

Q: In the circuit shown, there will be a non-zero reading in galvanometer G: A) only just after S is closed B) only just after S is opened C) only while S is kept closed D) never E) only just after S is opened or closed

Q: The emf developed in a coil X due to the current in a neighboring coil Y is proportional to the: A) magnetic field in X B) rate of change of magnetic field in X C) resistance of X D) thickness of the wire in X E) current in Y

Q: If the magnetic flux through a certain region is changing with time: A) energy must be dissipated as heat B) an electric field must not exist at the boundary C) a current must flow around the boundary D) an emf must exist around the boundary E) a magnetic field must exist at the boundary

Q: Faraday's law states that an induced emf is proportional to: A) the rate of change of the magnetic field B) the rate of change of the electric field C) the rate of change of the magnetic flux D) the rate of change of the electric flux E) zero

Q: In the experiment shown: A) there is a steady reading in G as long as S is closed B) a motional emf is generated when S is closed C) the current in the battery goes through G D) there is a current in G just after S is opened or closed E) since the two loops are not connected, the current in G is always zero

Q: A uniform magnetic field makes an angle of 30ï‚°with the zaxis. If the magnetic flux through a 1.0 m2portion of the xyplane is 5.0Wb then the magnetic flux through a 2.0 m2portion of the same plane is: A) 2.5 Wb B) 4.3 Wb C) 5.0Wb D) 5.8 Wb E) 10 Wb

Q: A 2.0 T uniform magnetic field makes an angle of 30ï‚°with the zaxis. The magnetic flux through a 3.0 m2portion of the xyplane is: A) 2.0 Wb B) 3.0 Wb C) 5.2 Wb D) 6.0Wb E) 12 Wb

Q: Suppose this page is perpendicular to a uniform magnetic field and the magnetic flux through it is 5.0Wb. If the page is turned by 30ï‚°around an edge the flux through it will be: A) 2.5 Wb B) 4.3 Wb C) 5.0Wb D) 5.8 Wb E) 10 Wb

Q: The normal to a certain 1.0 m2area makes an angle of 60ï‚°with a uniform magnetic field. The magnetic flux through this area is the same as the flux through a second area that is perpendicular to the field if the second area is: A) 0.50 m2 B) 0.87 m2 C) 1.0 m2 D) 1.2 m2 E) 2.0 m2

Q: The magnetic flux ΦBthrough a surface: A) is the amount of magnetic field piercing the surface. B) is the magnetic field multiplied by the area. C) does not depend on the area involved. D) is the line integral of the magnetic field around the edge of the surface. E) is the amount of magnetic field skimming along the surface.

Q: The units of motional emf are:A) volt/secondB) volt.meter/secondC) volt/teslaD) tesla/secondE) tesla.meter2/second

Q: 1 weber is the same as:A) 1 V.sB) 1 T.sC) 1 T/mD) 1 V/sE) 1 T/m2

Q: 1 weber is the same as: A) 1 V/s B) 1 T/s C) 1 T/m D) 1 Tm2 E) 1 T/m2

Q: The emf that appears in Faraday's law is: A) around a conducting circuit B) around the boundary of the surface used to compute the magnetic flux C) throughout the surface used to compute the magnetic flux D) perpendicular to the surface used to compute the magnetic flux E) none of the above

Q: Two coils have a mutual inductance of 3.5 mH. If the current in one coil is changing at a rate of 4.8 A/s, what is the emf induced in the second coil? A) 7.3 x 10-4V B) 0.017 V C) 1400 V D) cannot tell without knowing the inductance of the second coil E) cannot tell without knowing the current in the second coil

Q: In the diagram, assume that all the magnetic field lines generated by coil 1 pass through coil 2. Coil 1 has 100 turns and coil 2 has 400 turns. Then: A) the currents will be the same in the two coils B) the emf around coil 1 will be 1/4 the emf around coil 2 C) the current in coil 1 will be 1/4 the current in coil 2 D) the emfs will be the same in the two coils E) none of the above

Q: A 0.20-cm radius cylinder, 3.0 cm long, is wrapped with wire to form an inductor. At the instant the magnetic field in the interior is 5.0 mT, the energy stored in the field is:A) 0 JB) 3.8 x10-6JC) 7.5 x10-6JD) 7.5 x10-4 JE) 9.9 J

Q: The quantity (B2/) has units of:A) JB) J/HC) J/mD) J/m3E) H/m3

Q: A 6.0-mH inductor and a 3.0-resistor are wired in series to a 12-V ideal battery. A switch in the circuit is closed at time t= 0, at which time the current is zero. 2.0 ms later the energy stored in the inductor is:A) 0 JB) 9.6 x10-3JC) 1.9 x10-2JD) 2.5 x10-2JE) 3.8x10-2J

Q: A 6.0 mH inductor is in a series circuit with a resistor and an ideal battery. At the instant the current in the circuit is 5.0 A the energy stored in the inductor is:A) 0 JB) 7.5 x10-2JC) 15 x10-2JD) 30 x10-2JE) unknown since the rate of change of the current is not given

Q: A current of 10 A in a certain inductor results in a stored energy of 40 J. When the current is changed to 5 A in the opposite direction, the stored energy changes by: A) 20 J B) 30 J C) 40 J D) 50 J E) 60 J

Q: If Ris the distance from a magnetic dipole, then the magnetic field it produces is proportional to: A) R2 B) R C) 1/R D) 1/R2 E) 1/R3

Q: A 45-m long wire is coiled so that it makes a coil containing 100 circular loops, one on top of the other. If the wire carries a current of 13 A, what is the magnetic dipole moment of the coil? A) 21 Am2 B) 6.7 Am2 C) 3.3 Am2 D) 2.6 Am2 E) 1.2 Am2

Q: A square loop of current-carrying wire with edge length ais in the xyplane, the origin being at its center. Along which of the following lines can a charge move without experiencing a magnetic force? A) x= 0, y= a/2 B) x= a/2, y= a/2 C) x= a/2, y= 0 D) x= 0, y= 0 E) x= 0, z= 0

Q: The diagram shows three arrangements of circular loops, centered on vertical axes and carrying identical currents in the directions indicated. Rank the arrangements according to the magnitudes of the magnetic fields at the midpoints between the loops on the central axes, from least to greatest.A) 1, 2, 3B) 2, 1, 3C) 2, 3, 1D) 3, 2, 1E) 3, 1, 2

Q: A toroid has a square cross section with the length of an edge equal to the radius of the inner surface. The ratio of the magnitude of the magnetic field at the inner surface to the magnitude of the field at the outer surface is: A) 1/4 B) 1/2 C) 1 D) 2 E) 4

Q: A toroid with a square cross section carries current i. The magnetic field has its largest magnitude: A) at the center of the hole B) just inside the toroid at its inner surface C) just inside the toroid at its outer surface D) at any point inside (the field is uniform) E) at none of the above

Q: A solenoid is 3.0 cm long and has a radius of 0.50 cm. It is wrapped with 500 turns of wire carrying a current of 2.0 A. The magnetic field at the center of the solenoid is:A) 9.9 x10-8TB) 1.3 x10-3TC) 4.2 x10-2TD) 16 TE) 20 T

Q: Solenoid 2 has twice the radius and six times the number of turns per unit length as solenoid 1. The ratio of the magnetic field in the interior of 2 to that in the interior of 1 is: A) 1/3 B) 1 C) 2 D) 4 E) 6

Q: Two long ideal solenoids (with radii 20 mm and 30 mm respectively) have the same number of turns of wire per unit length. The smaller solenoid is mounted inside the larger, along a common axis. It is observed that there is zero magnetic field within the inner solenoid. The current in the inner solenoid must be: A) two-thirds the current in the outer solenoid B) one-third the current in the outer solenoid C) twice the current in the outer solenoid D) half the current in the outer solenoid E) the same as the current in the outer solenoid

Q: Magnetic field lines inside the solenoid shown are: A) clockwise circles as one looks down the axis from the top of the page B) counterclockwise circles as one looks down the axis from the top of the page C) toward the top of the page D) toward the bottom of the page E) in no direction since B= 0

Q: The magnetic field inside a long ideal solenoid is independent of: A) the current B) the number of turns of wire C) the spacing of the windings D) the cross-sectional area E) the direction of the current

Q: A long straight cylindrical shell has an inner radius Riand an outer radius Ro. It carries a current i, uniformly distributed over its cross section. A wire is parallel to the cylinder axis, in the hollow region (r<Ri). The magnetic field is zero everywhere in the hollow region. We conclude that the wire: A) is on the cylinder axis and carries current iin the same direction as the current in the shell B) may be anywhere in the hollow region but must be carrying current iin the direction opposite to that of the current in the shell C) may be anywhere in the hollow region but must be carrying current iin the same direction as the current in the shell D) is on the cylinder axis and carries current iin the direction opposite to that of the current in the shell E) does not carry any current