PHY 20

A charged particle moving along the +x-axis enters a uniform magnetic field pointing along the +z-axis. A uniform electric field is also present. Due to the combined effect of both fields, the particle does not change its velocity. What is the direction of the electric field? A) along the -y-axis B) along the +y-axis C) along the -x-axis D) along the +x-axis E) along the -z-axis

B

If a calculated quantity has units of N/Am , that quantity could be A) an electric field. B) an electric potential. C) μ0. D) a magnetic field. E) a magnetic torque.

D

A positive charge is moving to the right and experiences an upward magnetic force, as shown in the figure. In which direction must the magnetic field have a component? A) to the right B) to the left C) upward D) out of the page E) into the page

E

A charged particle is observed traveling in a circular path of radius R in a uniform magnetic field. If the particle were traveling twice as fast, the radius of the circular path would be A) 2R. B) 4R. C) 8R. D) R/2. E) R/4.

A

A long, straight, horizontal 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 magnetic force on the proton? A) toward the north B) toward the south C) upward D) downward E) toward the east.

A

A proton, moving east, enters a magnetic field. Because of this magnetic field the proton curves downward. We may conclude that the magnetic field must have a component A) towards the south. B) towards the north. C) towards the west. D) upward. E) downward.

A

An electron has an initial velocity to the south but is observed to curve upward as the result of a magnetic field. This magnetic field must have a component A) to the west. B) to the east. C) upward. D) downward. E) to the north.

A

An electron is moving to the right, as shown in the figure. Suddenly it encounters uniform magnetic field pointing out of the page. Which one of the three paths shown will it follow in the field? A) path a B) path b C) path c

A

An electron, moving west, enters a magnetic field. Because of this field the electron curves upward. We may conclude that the magnetic field must have a component A) towards the north. B) towards the south. C) upward. D) downward. E) towards the west.

A

An object is hung using a metal spring. If now a current is passed through the spring, what will happen to this system? A) The spring will contract, raising the weight. B) The spring will extend, lowering the weight. C) The weight will not move. D) The spring will begin to swing like a pendulum. E) None of these are true.

A

Consider an ideal solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire windings. If the radius of the solenoid is doubled to 2b, but all the other quantities remain the same, the magnetic field inside the solenoid will A) remain the same. B) become twice as strong as initially. C) become one-half as strong as initially. D) become four times as strong as initially. E) become one-fourth as strong as initially.

A

The magnetic field at a distance of 2 cm from a long straight current-carrying wire is 4 μT. What is the magnetic field at a distance of 4 cm from this wire? A) 2 μT B) 4 μT C) 6 μT D) 8 μT E) 10 μT

A

The maximum torque on a flat current-carrying loop occurs when the angle between the plane of the loop's area and the magnetic field vector is A) 0° B) 45° C) 90° D) 135°

A

When you double the number of windings in an ideal solenoid while keeping all other parameters (radius, length and current) fixed, the magnetic field at the center of the solenoid will A) double. B) triple. C) quadruple. D) be reduced by a factor of one-half. E) be reduced by a factor of one-fourth.

A

A long, straight, horizontal wire carries current toward the east. An electron moves toward the east alongside and just south of the wire. What is the direction of the magnetic force on the electron? A) toward the north B) toward the south C) upward D) downward E) toward the west.

B

A proton has an initial velocity to the south but is observed to curve upward as the result of a magnetic field. This magnetic field must have a component A) to the west. B) to the east. C) upward. D) downward. E) to the north.

B

A straight bar magnet is initially 4 cm long, with the north pole on the right and the south pole on the left. If you cut the magnet in half, the right half will A) contain only a north pole. B) contain a north pole on the right and a south pole on the left. C) contain only a south pole. D) no longer contain any poles.

B

An electron moving along the +x-axis enters a magnetic field. If the electron experiences a magnetic deflection in the -y direction, then the magnetic field must have a component A) along the +z-axis B) along the -z-axis C) along the -x-axis D) along the +y-axis E) along the -y-axis

B

In a velocity selector consisting of perpendicular electric and magnetic fields, the speeds of the charged particles passing through the selector are increased or decreased until they are equal to the desired speed. A) True B) False

B

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 directly toward you, and the wire on your left carries current directly away from you. From your point of view, the magnetic field at a point exactly midway between the two wires A) points upward. B) points downward. C) points toward you. D) points away from you. E) is zero.

B

Two long, parallel wires carry currents of different magnitudes. If the current in one of the wires is doubled and the current in the other wire is halved, what happens to the magnitude of the magnetic force that each wire exerts on the other? A) It is doubled. B) It stays the same. C) It is tripled. D) It is quadrupled. E) It is reduced by a factor of two.

B

Which one of the following statements is correct? A) When a current-carrying wire is in your right hand, with your thumb in the direction of the current, your fingers point opposite to the direction of the magnetic field lines. B) When a current-carrying wire is in your right hand, with your 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 left hand, with your thumb in the direction of the current, your fingers point in the direction of the magnetic field lines.

B

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 strongest when the particle moves A) straight upward. B) straight downward. C) in a plane parallel to Earth's surface. D) upward at an angle of 45° above the horizontal.

C

A charged particle moving along the +x-axis enters a uniform magnetic field pointing along the +z-axis. Because of an electric field along the +y-axis, the charge particle does not change velocity. What is the sign of this particle? A) positive B) negative C) The particle could be either positive or negative. D) None of the above choices is correct.

C

A charged particle that is moving in a static uniform magnetic field A) will always experience a magnetic force, regardless of its direction of motion. B) may experience a magnetic force which will cause its speed to change. C) may experience a magnetic force, but its speed will not change. D) may experience a magnetic force, but its direction of motion will not change. E) None of the above statements are true.

C

A flat 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 due to the magnetic torque on the loop? A) the north side B) the east side C) the south side D) the west side E) The entire loop lifts straight up.

C

A negatively-charged particle moves across a constant uniform magnetic field that is perpendicular to the velocity of the particle. The magnetic force on this particle A) causes the particle to speed up. B) causes the particle to slow down. C) causes the particle to accelerate. D) is in the same direction as the particle's velocity. E) is opposite the direction of the particle's velocity.

C

A proton, moving in a uniform magnetic field, moves in a circle perpendicular to the field lines and takes time T for each circle. If the proton's speed tripled, what would now be its time to go around each circle? A) 9T B) 3T C) T D) T/3 E) T/9

C

A proton, moving north, enters a magnetic field. Because of this field, the proton curves downward. We may conclude that the magnetic field must have a component A) downward. B) upward. C) towards the east. D) towards the west. E) towards the north.

C

A proton, moving west, enters a magnetic field. Because of this magnetic field the proton curves upward. We may conclude that the magnetic field must have a component A) towards the west. B) towards the east. C) towards the south. D) towards the north. E) downward.

C

A vertical wire carries a current vertically downward. To the east of this wire, the magnetic field points A) north. B) east. C) south. D) down.

C

A very long straight current-carrying wire produces a magnetic field of 20 mT at a distance d from the wire. To measure a field of 5 mT due to this wire, you would have to go to a distance from the wire of A) 16d. B) 8d. C) 4d. D) 2d. E) d

C

A wire is carrying current vertically downward. What is the direction of the force on this wire due to Earth's magnetic field? A) horizontally towards the north B) horizontally towards the south C) horizontally towards the east D) horizontally towards the west E) vertically upward

C

After landing on an unexplored Klingon planet, Spock tests for the direction of the magnetic field by firing a beam of electrons in various directions and by recording the following observations: Electrons moving upward feel a magnetic force in the northwest direction. Electrons moving horizontally toward the north are pushed downward. Electrons moving horizontally toward the southeast are pushed upward. Mr. Spock therefore concludes that the magnetic field at this landing site is in which direction? A) toward the east B) toward the northeast C) toward the southwest D) toward the southeast E) toward the west

C

At a particular instant, a proton moves toward the east in a uniform magnetic field that is directed straight downward. The magnetic force that acts on it is A) zero. B) upward. C) toward the north. D) toward the south. E) downward.

C

Consider an ideal solenoid of length L, N windings, and radius b (L is much longer than b). A current I is flowing through the wire windings. If the length of the solenoid becomes twice as long (to 2L), but all other quantities remained the same, the magnetic field inside the solenoid will A) remain the same. B) become twice as strong as initially. C) become one-half as strong as initially. D) become four times as strong as initially. E) become one-fourth as strong as initially.

C

If a calculated quantity has units of T ∙ m/A, that quantity could be A) an electric field. B) an electric potential. C) μ0. D) a magnetic field. E) a magnetic torque.

C

If you were to cut a small permanent bar magnet in half, A) one piece would be a magnetic north pole and the other piece would be a south pole. B) neither piece would be magnetic. C) each piece would in itself be a smaller bar magnet with both north and south poles. D) None of these statements is true.

C

The direction of the force on a current-carrying wire in a magnetic field is A) perpendicular only to the current. B) perpendicular only to the magnetic field. C) perpendicular to both the current and the magnetic field. D) in the direction opposite to the current. E) in same direction as the current.

C

Two long parallel wires are placed side-by-side on a horizontal table and carry current in the same direction. The current in one wire is 20 A, and the current in the other wire is 5 A. If the magnetic force on the 20-A wire has magnitude F, what is the magnitude of the magnetic force on the 5-A wire? No external magnetic fields are present. A) 4F B) 2F C) F D) F/2 E) F/4

C

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 while the other wire is forced downward against the table's surface. B) both wires are lifted slightly. C) the wires pull toward each other. D) the wires push away from each other.

C

When a ferromagnetic material is placed in an external magnetic field, the net magnetic field of its magnetic domains becomes A) smaller. B) zero. C) larger.

C

When two long parallel wires carry unequal currents, the magnitude of the magnetic force that one wire exerts on the other is F. If the current in both wires is now doubled, what is the magnitude of the new magnetic force on each wire? A) 16F B) 8F C) 4F D) 2F E) F

C

Which one of the following statements is correct? A) Earth's geographic north pole is the north pole of Earth's magnetic field. B) Earth's geographic south pole is the south pole of Earth's magnetic field. C) The north pole of a magnet points towards Earth's geographic north pole. D) The north pole of a magnet points towards Earth's geographic south pole. E) None of the above statements is correct.

C

A charged particle is injected into a uniform magnetic field such that its velocity vector is perpendicular to the magnetic field lines. Ignoring the particle's weight, the particle will A) move in a straight line. B) follow a spiral path. C) move along a parabolic path. D) follow a circular path.

D

A horizontal wire carries a current straight toward you. From your point of view, the magnetic field caused by this current A) points directly away from you. B) points to the left. C) circles the wire in a clockwise direction. D) circles the wire in a counter-clockwise direction.

D

A long, straight wire carrying a current is placed along the y-axis. If the direction of the current is in the +y direction, what is the direction of the magnetic field due to this wire as you view it in such a way that the current is coming directly toward you? A) clockwise, around the x-axis B) counterclockwise, around the x-axis C) counterclockwise, around the z-axis D) counterclockwise, around the y-axis E) clockwise, around the y-axis

D

A particle carrying a charge of +e travels in a circular path of radius R in a uniform magnetic field. If instead the particle carried a charge of +2e, the radius of the circular path would have been A) 2R. B) 4R. C) 8R. D) R/2. E) R/4.

D

A vertical wire carries a current straight up in a region where the magnetic field vector points toward the north. What is the direction of the magnetic force on this wire? A) downward B) toward the north C) toward the east D) toward the west E) upward F) toward the south

D

An electron, moving south, enters a magnetic field. Because of this field, the electron curves upward. We may conclude that the magnetic field must have a component A) downward. B) towards the east. C) upward. D) towards the west. E) towards the north.

D

At a particular instant, an electron moves toward the east in a uniform magnetic field that is directed straight downward. The magnetic force that acts on it is A) zero. B) upward. C) toward the north. D) toward the south. E) downward.

D

If a calculated quantity has units of Ns/Cm , that quantity could be A) an electric field. B) an electric potential. C) μ0. D) a magnetic field. E) a magnetic torque.

D

The magnetic field at a distance of 2 cm from a long straight current-carrying wire is 4 μT. What is the magnetic field at a distance of 1 cm from this wire? A) 2 μT B) 4 μT C) 6 μT D) 8 μT E) 10 μT

D

The magnetic force on a current-carrying wire in a magnetic field is the strongest when A) the current is in the direction of the magnetic field lines. B) the current is in the direction opposite to the magnetic field lines. C) the current is at a 180° angle with respect to the magnetic field lines. D) the current is perpendicular to the magnetic field lines. E) the current is at a 0° angle with respect to the magnetic field lines.

D

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 while the other wire is forced downward against the table's surface. B) both wires are lifted slightly. C) the wires pull toward each other. D) the wires push away from each other.

D

Two long, parallel wires carry currents of different magnitudes. If the amount of current in one of the wires is doubled, what happens to the magnitude of the force that each wire exerts on the other? A) It is increased by a factor of 8. B) It is increased by a factor of 4. C) It is increased by a factor of 3. D) It is increased by a factor of 2. E) It is increased by a factor of

D

We observe that a moving charged particle experiences no magnetic force. From this we can definitely conclude that A) no magnetic field exists in that region of space. B) the particle must be moving parallel to the magnetic field. C) the particle is moving at right angles to the magnetic field. D) either no magnetic field exists or the particle is moving parallel to the field. E) either no magnetic field exists or the particle is moving perpendicular to the field.

D

A proton is to orbit Earth at the equator using Earth's magnetic field to supply part of the necessary centripetal force. In what direction should the proton move? A) upward B) northward C) southward D) eastward E) westward

E

A wire lying in the plane of this page carries a current directly toward the top of the page. What is the direction of the magnetic force this current produces on an electron that is moving perpendicular to the page and outward from it on the left side of the wire? A) perpendicular to the page and towards you B) perpendicular to the page and away from you C) toward the top of the page D) toward the bottom of the page E) The force is zero.

E

An electron moving in the +y direction, at right angles to a magnetic field, experiences a magnetic force in the -x direction. The direction of the magnetic field is in the A) -x direction. B) +x direction. C) +y direction. D) -z direction. E) +z direction.

E

In a certain velocity selector consisting of perpendicular electric and magnetic fields, the charged particles move toward the east, and the magnetic field is directed to the north. What direction should the electric field point? A) toward the east B) toward the west C) toward the south D) upward E) downward

E

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 a point exactly between the two wires A) points upward. B) points downward. C) points toward you. D) points away from you. E) is zero.

E