Week 6 Quiz

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 one-half as strong as initially. c) become one-fourth as strong as initially. d) become four times as strong as initially. e) become twice as strong as initially.

a

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

a

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) follow a spiral path. b) follow a circular path. c) move in a straight line. d) move along a parabolic path.

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) in a plane parallel to Earth's surface. c) upward at an angle of 45° above the horizontal. d) straight downward.

b

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 -z axis b) Along the +y axis c) Along the +x axis d) Along the -y axis e) Along the -x axis

b

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) The particle could be either positive or negative. c) None of the above choices is correct. d) negative

b

A current-carrying loop of wire lies flat on a horizontal tabletop. When viewed from above, the current moves around the loop in a counterclockwise sense. For points on the tabletop outside the loop, the magnetic field lines caused by this current a) point straight up. b) point straight down. c) circle the loop in a counterclockwise direction. d) circle the loop in a clockwise direction.

b

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) 8R. b) R/2. c) 4R. d) R/4. e) 2R.

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) Upward b) To the east c) Downward d) To the north e) To the east

b

A single current carrying circular loop of radius R is placed next to a long straight wire as shown in the figure The current I in the wire flows to the right. In which direction must current flow in the loop to produce a net magnetic field of zero at its center a) counterclockwise b) clockwise c) It could be either clockwise or counterclockwise d) The current in the loop should be zero

b

A vertical wire carries a current vertically downward. To the east of this wire, the magnetic field points a) north. b) south. c) down. d) east.

b

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

b

A charged particle that is moving in a static uniform magnetic field a) None of the above 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) Will always experience a magnetic force regardless of its direction of motion e) May experience a magnetic force but its direction of motion will not change

c

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

c

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) Counterclockwise around the z-axis b) Clockwise around the y axis c) Counterclockwise around y-axis d) Clockwise around the x-axis e) Counterclockwise around the x-axis

c

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) downward b) toward the north (not this one) c) upward d) toward the west. e) toward the south

c

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) out of the page b) upward c) into the page d) to the left e) straight down

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) Towards the north b) Downwards c) Towards the east d) Toward the west e) Upward

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 north. b) downward. c) towards the south. d) towards the east. e) towards the west.

c

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) upward. b) downward. c) toward the south. d) zero. e) toward the north.

c

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) downward b) upward c) toward the east. d) toward the north e) toward the south

d

A negatively charged particle -Q is moving to the right directly above a wire having a current I flowing to the right as shown in the figure in what direction is the magnetic force exerted on the particle due to the current a) Into the page b) Downward c) The magnetic force is zero because the velocity is parallel to the current d) Upward e) Out of the page

d

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) is in the same direction as the particle's velocity. c) is opposite the direction of the particle's velocity. d) causes the particle to accelerate. e) causes the particle to slow down.

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) eastward b) southward c) northward d) westward e) upward

d

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) T/9 b) 9T c) 3T d) T e) T/3

d

A ring with a clockwise current (as viewed from above the ring) is situated with its center directly above another ring, which has a counter- clockwise current, as shown in the figure. In what direction is the net magnetic force exerted on the top ring due to the bottom ring a) The net force is zero b) Downward c) To the left d) Upward e) To the right

d

A vertical wire carries a current straight up in a region where the magnetic field vector points towards the north. What is the direction of the magnetic force on this wire? a) Towards the east b) Upward c) Towards the south d) Towards the west e) Towards the north f) Downward

d

A wire lying in the plane of the page carries a current towards the bottom of the page as shown in the figure What is the direction of the magnetic force it produces on an electron that is moving to the left directly towards the wire as shown a) Directly to the left away from the wire b) Directly towards the top of the page c) Straight into the page d) Directly toward the bottom of the page e) Straight out of the page

d

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

d

4. 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) R/4. b) 4R. c) 8R. d) R/2. e) 2R.

e

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) Downward b) Upward c) Towards the north d) Towards the west e) Towards the south

e

A wire is carrying current vertically downward. What is the direction of the force of this wire due to earth's magnetic field? a) Horizontally towards the south b) Vertically upward c) Horizontally towards the north d) Horizontally towards the west e) Horizontally towards the east

e

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) become one-fourth as strong as initially. b) remain the same. c) become four times as strong as initially. d) become twice as strong as initially. e) become one-half as strong as initially.

e