AP Physics B: Ch 20 Magnetism and Ch 21 EM Induction

Transcription

1 Name: Period: Date: AP Physics B: Ch 20 Magnetism and Ch 21 EM Induction MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) If the north poles of two bar magnets are brought close to each other, the magnets will A) attract. B) repel. 1) 2) If the south pole of one bar magnet is brought near the north pole of a second bar magnet, the two magnets will A) repel. B) attract. 2) 3) If a bar magnet is divided into two equal pieces, A) an electric field is created. B) the north and south poles are separated. C) two magnets result. D) the magnet properties are destroyed. 3) 4) The Earth's geographic North Pole is magnetically a A) south pole. B) north pole. 4) 5) The south pole of a magnet points toward the Earth's A) center. B) North Pole. C) middle latitudes. D) South Pole. 5) 6) An electric current produces A) a gravitational field. B) an electromagnetic field. C) a magnetic field. D) an electric field. 6) 7) Which of the following is correct? A) When a current carrying wire is in your right hand, thumb in the direction of the current, your fingers point in the direction of the magnetic field lines. B) When a current carrying wire is in your left hand, thumb in the direction of the current, your fingers point in the direction of the magnetic field lines. C) When a current carrying wire is in your right hand, thumb in the direction of the magnetic field lines, your fingers point in the direction of the current. D) When a current carrying wire is in your left hand, thumb in the direction of the magnetic field lines, your fingers point in the direction of the current. 7) 8) A vertical wire carries a current straight down. To the east of this wire, the magnetic field points A) south. B) east. C) north. D) down. 8) 9) A horizontal wire carries a current straight toward you. From your point of view, the magnetic field caused by this current A) circles the wire in a counter-clockwise direction. B) points to the left. C) circles the wire in a clockwise direction. D) points directly away from you. 9) 1

2 10) A current carrying loop of wire lies flat on a table top. When viewed from above, the current moves around the loop in a counterclockwise sense. What is the direction of the magnetic field caused by this current, outside the loop? The magnetic field A) points straight down. B) circles the loop in a counterclockwise direction. C) circles the loop in a clockwise direction. D) points straight up. 10) 11) A current carrying circular loop of wire lies flat on a table top. When viewed from above, the current moves around the loop in a counterclockwise sense. What is the direction of the magnetic field caused by this current, inside the loop? The magnetic field A) points straight down. B) circles the loop in a clockwise direction. C) circles the loop in a counterclockwise direction. D) points straight up. 11) 12) The SI unit of magnetic field is the A) gauss. B) tesla. C) lorentz. D) weber. 12) 13) 1 T is equivalent to A) V m/a. B) 1 N m/a. C) 1 N A/m. D) N/A m. 13) 14) The direction of the force on a current-carrying wire in a magnetic field is described by which of the following? A) perpendicular to the current only B) perpendicular to the magnetic field only C) perpendicular to both the current and the magnetic field D) perpendicular to neither the current or the magnetic field 14) 15) The force on a current-carrying wire in a magnetic field is the strongest when A) the current is perpendicular to the field lines. B) the current is at a 30 angle with respect to the field lines. C) the current is parallel to the field lines. D) the current is at a 60 angle with respect to the field lines. 15) 16) The force on a current-carrying wire in a magnetic field is equal to zero when A) the current is perpendicular to the field lines. B) the current is at a 60 angle with respect to the field lines. C) the current is at a 30 angle with respect to the field lines. D) the current is parallel to the field lines. 16) 17) A vertical wire carries a current straight up in a region where the magnetic field vector points due north. What is the direction of the resulting force on this current? A) east B) west C) down D) north 17) 2

3 18) A charged particle moves and experiences no magnetic force. From this we can conclude that A) the particle is moving parallel to the magnetic field. B) the particle is moving at right angles to the magnetic field. C) either no magnetic field exists or the particle is moving parallel to the field. D) no magnetic field exists in that region of space. 18) 19) A charged particle moves with a constant speed through a region where a uniform magnetic field is present. If the magnetic field points straight upward, the magnetic force acting on this particle will be maximum when the particle moves A) upward at an angle of 45 above the horizontal. B) straight downward. C) in a plane parallel to the Earth's surface. D) straight upward. 19) 20) A charged particle moves across a constant magnetic field. The magnetic force on this particle A) is in the direction of the particle's motion. B) causes the particle to accelerate. C) changes the particle's speed. D) changes the particle's speed causing the particle to accelerate. 20) 21) A charged particle is injected into a uniform magnetic field such that its velocity vector is perpendicular to the magnetic field vector. Ignoring the particle's weight, the particle will A) follow a spiral path. B) move along a parabolic path. C) follow a circular path. D) move in a straight line. 21) 22) A charged particle is observed traveling in a circular path in a uniform magnetic field. If the particle had been traveling twice as fast, the radius of the circular path would be A) twice the original radius. B) four times the original radius. C) one-fourth the original radius. D) one-half the original radius. 22) 23) A particle carrying a charge of +e travels in a circular path in a uniform magnetic field. If instead the particle carried a charge of +2e, the radius of the circular path would have been A) twice the original radius. B) one-half the original radius. C) four times the original radius. D) one-fourth the original radius. 23) 24) At a particular instant, an electron moves eastward at speed V in a uniform magnetic field that is directed straight downward. The magnetic force that acts on it is A) directed to the south. B) directed upward. C) zero. D) directed to the north. 24) 25) An electron has an initial velocity to the south but is observed to curve upward as the result of a magnetic field. The direction of the magnetic field is A) downward. B) to the west. C) upward. D) to the east. 25) 26) An electron moving along the +x axis enters a region where there is a uniform magnetic field in the +y direction. What is the direction of the magnetic force on the electron? (+x to right, +y up, and +z out of the page.) A) +z direction B) -z direction C) -x direction D) -y direction 26) 3

4 27) The magnetic field produced by a long straight current-carrying wire is A) inversely proportional to both the current in the wire and the distance from the wire. B) inversely proportional to the current in the wire and proportional to the distance from the wire. C) proportional to the current in the wire and inversely proportional to the distance from the wire. D) proportional to both the current in the wire and the distance from the wire 27) 28) At double the distance from a long current-carrying wire, the strength of the magnetic field produced by that wire decreases to A) 1/2 of its original value. B) 1/8 of its original value. C) 1/4 of its original value. D) none of the given answers 28) 29) Two long parallel wires placed side-by-side on a horizontal table carry identical size currents in opposite directions. The wire on your right carries current toward you, and the wire on your left carries current away from you. From your point of view, the magnetic field at the point exactly midway between the two wires A) points down. B) points toward you. C) points up. D) is zero. 29) 30) Two long parallel wires placed side-by-side on a horizontal table carry identical current straight toward you. From your point of view, the magnetic field at the point exactly between the two wires A) points up. B) points down. C) is zero. D) points toward you. 30) 31) Two long parallel wires carry equal currents. The magnitude of the force between the wires is F. The current in each wire is now doubled. What is the magnitude of the new force between the two wires? A) F/4 B) 4F C) 2F D) F/2 31) 32) A long straight wire carries current toward the east. A proton moves toward the east alongside and just south of the wire. What is the direction of the force on the proton? A) up B) north C) south D) down 32) 33) A wire lying in the plane of the page carries a current toward the bottom of the page. What is the direction of the magnetic force it produces on an electron that is moving perpendicularly toward the wire, also in the plane of the page, from your right? A) zero B) toward the bottom of the page C) toward the top of the page D) perpendicular to the page and towards you E) perpendicular to the page and away from you 33) 34) Two long parallel wires are placed side-by-side on a horizontal table. If the wires carry current in the same direction, A) one wire is lifted slightly as the other wire is forced against the table's surface. B) both wires are lifted slightly. C) the wires repel each other. D) the wires attract each other. 34) 4

5 35) Two long parallel wires are placed side-by-side on a horizontal table. If the wires carry current in opposite directions, A) one wire is lifted slightly as the other is forced against the table's surface. B) the wires attract each other. C) both wires are lifted slightly. D) the wires repel each other. 35) 36) Consider two current-carrying circular loops. Both are made from one strand of wire and both carry the same current, but one has twice the radius of the other. Compared to the magnetic field at the center of the smaller loop, the magnetic field at the center of the larger loop is A) 2 times stronger. B) 8 times stronger. C) 4 times stronger. D) none of the given answers 36) 37) Consider two current-carrying circular loops. Both are made from one strand of wire and both carry the same current, but one has twice the radius of the other. Compared to the magnetic moment of the smaller loop, the magnetic moment of the larger loop is A) 4 times stronger. B) 16 times stronger. C) 2 times stronger. D) 8 times stronger. 37) 38) The maximum torque on a current carrying loop occurs when the angle between the loop's magnetic moment and the magnetic field vector is A) 180 B) 0 C) 90 D) none of the given answers 38) 39) When placed askew in a magnetic field, a current carrying loop that is free to rotate in any direction will experience a torque until its magnetic moment vector A) is at right angles to the magnetic field vector. B) is aligned with the magnetic field vector. C) makes an angle of 270 with the magnetic field vector. D) makes a 45 angle with the magnetic field vector. 39) 40) What fundamental fact underlies the operation of essentially all electric motors? A) Opposite electric charges attract and like charges repel. B) Iron is the only element that is magnetic. C) A current-carrying conductor placed perpendicular to a magnetic field will experience a force. D) A magnetic north pole carries a positive electric charge, and a magnetic south pole carries a negative electric charge. E) Alternating current and direct current are both capable of doing work. 40) 41) A circular wire loop lies in a horizontal plane on a table and carries current in a counterclockwise direction when viewed from above. At this point, the Earth's magnetic field points to the north and dips below the horizontal. Which side of the coil tends to lift off of the table because of the torque caused by the currents interaction with the magnetic field? A) the north side B) the west side C) the east side D) the south side 41) 5

6 42) In a mass spectrometer a particle of mass m and charge q is accelerated through a potential difference V and allowed to enter a magnetic field B, where it is deflected in a semi-circular path of radius R. The magnetic field is uniform and oriented perpendicular to the velocity of the particle. Derive an expression for the mass of the particle in terms of B, q, V, and R. A) q2b2r2/(2v) B) qb2r2/v C) qb2r2/(2v) D) q2b2r2/v 42) 43) A velocity selector consists of a charged particle passing through crossed electric and magnetic fields. The forces exerted by these fields are in opposite directions, and only particles of a certain velocity will move in a straight line. In the following, disregard the magnitudes of the fields. In a velocity selector, the particles move toward the east, and the magnetic field is directed to the north. What direction should the electric field point? A) west B) down C) east D) up 43) 44) All of the following are units of magnetic flux except A) T m2. B) V s. C) T/V m. D) weber. 44) 45) Faraday's law of induction states that the emf induced in a loop of wire is proportional to A) the magnetic flux density times the loop's area. B) the time variation of the magnetic flux. C) current divided by time. D) the magnetic flux. 45) 46) Doubling the number of loops of wire in a coil produces what kind of change on the induced emf, assuming all other factors remain constant? A) The induced emf is twice times as much. B) The induced emf is 4 times as much. C) The induced emf is half as much. D) There is no change in the induced emf. 46) 47) Doubling the strength of the magnetic field through a loop of wire produces what kind of change on the induced emf, assuming all other factors remain constant? A) The induced emf is twice as much. B) The induced emf is 4 times as much. C) The induced emf is half as much. D) There is no change in the induced emf. 47) 48) Doubling the diameter of a loop of wire produces what kind of change on the induced emf, assuming all other factors remain constant? A) The induced emf is half as much. B) The induced emf is twice times as much. C) The induced emf is 4 times as much. D) There is no change in the induced emf. 48) 49) As a coil is removed from a magnetic field an emf is induced in the coil causing a current to flow within the coil. This current interacts with the magnetic field producing a force which A) acts in the direction opposite to the coil's motion. B) acts in the direction of the coil's motion. C) causes the coil to tend to flip over. D) acts at right angles to the coil's motion. 49) 6

7 50) 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 effects? A) oppose the effect which produces it B) produce a greater heating effect C) produce the greatest voltage D) enhance the effect which produces it 50) 51) A circular coil lies flat on a horizontal table. A bar magnet is held above its center with its north pole pointing down. The stationary magnet induces (when viewed from above) A) a counterclockwise current in the coil. B) no current in the coil. C) a clockwise current in the coil. D) a current whose direction cannot be determined from the information given. 51) 52) A circular coil lies flat on a horizontal table. A bar magnet is held above its center with its north pole pointing down, and released. As it approaches the coil, the falling magnet induces (when viewed from above) A) a clockwise current in the coil. B) a counterclockwise current in the coil. C) no current in the coil. D) a current whose direction cannot be determined from the information provided. 52) 53) A coil lies flat on a table top in a region where the magnetic field vector points straight up. The magnetic field vanishes suddenly. When viewed from above, what is the sense of the induced current in this coil as the field fades? A) The current flows clockwise initially, and then it flows counterclockwise before stopping. B) There is no induced current in this coil. C) The induced current flows clockwise. D) The induced current flows counterclockwise. 53) 54) A coil lies flat on a level table top in a region where the magnetic field vector points straight up. The magnetic field suddenly grows stronger. When viewed from above, what is the direction of the induced current in this coil as the field increases? A) clockwise B) clockwise initially, then counterclockwise before stopping C) counterclockwise D) There is no induced current in this coil. 54) 55) A coil lies flat on a horizontal table top in a region where the magnetic field points straight down. The magnetic field disappears suddenly. When viewed from above, what is the direction of the induced current in this coil as the field disappears? A) clockwise initially, then counterclockwise before stopping B) counterclockwise C) clockwise D) There is no induced current in this coil. 55) 7

8 56) A long straight wire lies on a horizontal table and carries an ever-increasing current northward. Two coils of wire lie flat on the table, one on either side of the wire. When viewed from above, the induced current circles A) clockwise in both coils. B) counterclockwise in the east coil and clockwise in the west coil. C) clockwise in the east coil and counterclockwise in the west coil. D) counterclockwise in both coils. 56) 57) A bar magnet falls through a loop of wire with the north pole entering first. As the north pole enters the wire, the induced current will be (as viewed from above) A) counterclockwise. B) clockwise. C) zero. D) to top of loop. 57) 58) A circular loop of wire is rotated at constant angular speed about an axis whose direction can be varied. In a region where a uniform magnetic field points straight down, what must be the orientation of the loop's axis of rotation if the induced emf is to be zero? A) It must make an angle of 45 to the vertical. B) Any horizontal orientation will do. C) It must be vertical. D) none of the given answers 58) 59) A circular loop of wire is rotated at constant angular speed about an axis whose direction can be varied. In a region where a uniform magnetic field points straight down, what must be the orientation of the loop's axis of rotation if the induced emf is to be a maximum? A) It must make an angle of 45 to the vertical. B) Any horizontal orientation will do. C) It must be vertical. D) none of the given answers 59) 8