Physics Chapter 19 Magnetic Forces and Fields

A current carrying loop can be positioned in a magnetic field such that the net torque is equal to zero. True False

True

The field exerts a force on stationary charges. The field exerts a force on moving charges only. The force is proportional to the magnitude of the field exerting it. The magnitude of the force depends on the type (+ or - : North or south).

1: Electric Field 2: Magnetic Field 3: Both an electric and a magnetic field 4: Neither an electric field or a magnetic field

A charged particle is moving perpendicular to a magnetic field in a circle with radius r. The magnitude of the magnetic field is increased. Compared to the initial radius of circular path, the radius of the new path is... a. smaller. b. larger. c. equal in size.

A

A loose spiral spring is hung form the ceiling and a large current is sent through it. The coils move ... a. closer together. b. farther apart. c. they do not move at all.

A

A magnetic field is directed out of the page. Two charged particles enter from the top and take the paths shown in the figure. Which statement is correct? a. Particle 1 has a positive charge and particle 2 has a negative charge. b. Both particles are positively charged. c. Both particles are negatively charged. d. Particle one has a negative charge and particle 2 has a positive charge. e. The direction of the paths depends on the magnitude of the velocity, not on the sign of the charge.

A

A square coil and an equliladral triangular coil each have sides of length L. The triangular coil has twice as many turns as the square coil. If a the same current is sent through each coil, when the coils are placed in the same uniform magnetic field making an angle of 30° with the planes of the coils, which coil experiences the greater torque? a. the square coil b. the triangular coil c. Both coils experience the same torque. d. It depends on the magnitude of the magnetic field that the coils are placed in.

A

A straight wire is bent into the shape shown. Determine the net magnetic force on the wire. mc020-1.jpg Select one: a. Zero b. IBL in the +z direction c. IBL in the -z direction d. 1.7 IBL in the +z direction e. 1.4 IBL in the -z direction

A

From your perspective, the current in a ring is moving in a clockwise direction. In the center of the ring, what is the direction of the magnetic field? a. Into the ring. b. Is zero c. Out of the ring.

A

Geophysicists today generally attribute the existence of the Earth's magnetic field to which of the following? a. convection currents within the liquid interior b. iron ore deposits in the crust Incorrect c. nickel-iron deposits in the crust d. solar flares

A

The north end of a bar magnet is used to pick up a nail. The nail is then removed and the south end of the magnet is placed close to the nail. The nail itself in not magnetic. What will the nail do? a. The nail will also be attracted to the other pole. b. The nail will move away from the magnet. c. Nothing will happen.

A

The path of a charged particle moving parallel to a uniform magnetic field will be a: a. straight line. b. circle. c. ellipse. d. parabola.

A

What direction do the magnetic field lines point? a. From the North to South magnetic poles. b. From the South to North magnetic poles. c. Magnetic field lines do not have a direction since they go between poles. d. Form circles that go around the magnet.

A

A charged particle traveling in the plane of this screen enters the region of a uniform magnetic field pointing into the screen, as shown. The subsequent path of the particle in the region of the magnetic field could be represented by... Image showing three different possible paths for a charged particle in a magnetic field. a. path 1 b. path 2. c. path 3. d. paths 1 or 2. e. paths 2 or 3. f. paths 1 or 3. g. paths 1, 2, or 3. h. none of these paths would be possible.

B

A proton is released such that its initial velocity is from right to left across this page. The proton's path, however, is deflected in a direction toward the bottom edge of the page due to the presence of a uniform magnetic field. What is the direction of this field? a. out of the page b. into the page c. from bottom edge to top edge of the page d. from right to left across the page

B

Consider two long, straight parallel wires, each carrying a current I. If the currents are flowing in opposite directions: a. the two wires will attract each other. b. the two wires will repel each other. c. the two wires will exert a torque on each other. d. neither wire will exert a force on the other.

B

Different units can be used to measure the same physical quantity, differing only by some multiplicative factor. The cgs unit for magnetic field, the gauss, is equal to ________ tesla. Select one: a. 104 b. 10-4 c. 0.5 d. These units do not measure the same physical quantity.

B

The current in a long wire creates a magnetic field in the region around the wire. How is the strength of the field at distance r from the wire center related to the magnitude of the field? a. field directly proportional to r b. field inversely proportional to r c. field directly proportional to r2 d. field inversely proportional to r2

B

The magnetic field of the Earth is believed responsible for which of the following? a. deflection of both charged and uncharged cosmic rays b. deflection of charged cosmic rays c. ozone in the upper atmosphere d. solar flares

B

The magnetic pole of the Earth nearest the geographic North Pole corresponds to which of the following? a. a magnetic north pole b. a magnetic south pole c. a magnetic arctic pole d. a magnetic Antarctic pole

B

A charged particle enters a bubble chamber filled with liquid hydrogen with an initial kinetic energy, Ko. The particle travels in the horizontal plane in a magnetic field that is in the vertical direction. After a certain time, the particle's kinetic energy has been reduced by a factor of 2 due to collisions with hydrogen atoms. At this point, the radius of curvature of the particle's path ... a. has been reduced by a factor of 4. b. has been reduced by a factor of 2. c. has been reduced by a factor of √2. d. has increased by a factor of 4. e. has increased by a factor of 2. f. has increased by a factor of √2 g. is still the same as the original radius of curvature.

C

A circular current loop is placed in an external magnetic field. How is the torque related to the radius of the loop? a. directly proportional to radius b. inversely proportional to radius c. directly proportional to radius squared d. inversely proportional to radius squared

C

Consider a solenoid that is very long compared with its radius. Of the following choices, what is the most effective way to increase the magnetic field in the interior of the solenoid? a. Double its length, keeping the number of turns per unit length constant. b. Reduce the radius by half, keeping the number of turns per unit length constant. c. Overwrap the entire solenoid with an additional layer of the current-carrying wire. d. Double the radius, keeping the number of turns per unit length constant.

C

In a mass spectrometer, an ion will have a smaller radius for its circular path if: a. its speed is greater. b. its mass is greater. c. its charge is greater. d. the magnetic field is weaker.

C

The diagram below shows the position of a long straight wire perpendicular to the page and a set of directions labeled A through H. When the current in the wire is directed up out of the page, the direction of the magnetic field at point P is a. A. b. B. c. C. d. D. e. E.

C

The force exerted on a current-carrying wire located in an external magnetic field is directly proportional to which of the following? a. current strength b. field strength c. both the current and the field strength d. None of the above are valid.

C

The magnetic force on a point charge in a magnetic field is largest, for a given speed, when it a. moves in the direction of the magnetic field. b. moves in the direction opposite to the magnetic field. c. moves perpendicular to the magnetic field. d. has velocity components both parallel to and perpendicular to the field.

C

There is a current I flowing in a clockwise direction in a square loop of wire that is in the plane of the paper. If the magnetic field B is toward the right, and if each side of the loop has length L, then the net magnetic torque acting on the loop is: a. 2ILB. b. ILB. c. IBL2. d. zero.

C

Three types of particles enter a mass spectrometer like the one in your notes. The figure below shows where the particles strike the detector array. Rank the particles that arrive at a,b, and c by m/q ratio from the largest ratio to the smallest ratio. Image showing mass spec result with 3 spots, a is the closest to the exit of the velocity selector, then b and then c. a. a, b, c b. b, c, a c. c, b, a d. All their m/q ratios are equal.

C

Which diagram correctly shows the magnetic field lines created by a circular current loop in which current flows in the direction shown? a. b. c. d. e.

C

A coaxial cable has an inner cylindrical conductor surrounded by cylindrical insulation and an outer cylindrical conducting shell. The outer shell carries the same current but in the opposite direction from that in the inner conductor as shown. If the coaxial cable sits in a uniform magnetic field directed upwards with respect to the cable, the effect of the field on the cable is a. a net force to the left. b. a net force to the right. c. a net force upwards. d. no net force but a slight shift of the inner conductor to the left and the outer conductor to the right. e. no net force but a slight shift of the inner conductor to the right and the outer conductor to the left.

D

A coaxial cable has an inner cylindrical conductor surrounded by cylindrical insulation and an outer cylindrical conducting shell. The outer shell carries the same current but in the opposite direction from that in the inner conductor as shown. If the coaxial cable sits in a uniform magnetic field directed upwards with respect to the cable, the effect of the field on the cable is mc060-1.jpg Select one: a. a net force to the left. b. a net force to the right. c. a net force upwards. d. no net force but a slight shift of the inner conductor to the left and the outer conductor to the right. e. no net force but a slight shift of the inner conductor to the right and the outer conductor to the left.

D

A current in a long, straight wire produces a magnetic field. The magnetic field lines: a. go out from the wire to infinity. b. come in from infinity to the wire. c. form circles that pass through the wire. d. form circles that go around the wire.

D

A current loop is oriented in three different positions relative to a uniform magnetic field. In position 1 the plane of the loop is perpendicular to the field lines. In position 2 and 3 the plane of the loop is parallel to the field as shown. The torque on the loop is maximum in a. position 1. b. position 2. c. position 3 d. positions 2 and 3. e. all three positions.

D

There is a current I flowing in a clockwise direction in a square loop of wire that is in the plane of the paper. If the magnetic field B is toward the right, and if each side of the loop has length L, then the net magnetic force acting on the loop is: a. 2ILB. b. ILB. c. IBL2. d. zero.

D

A positively charge particle is moving to the right side of the screen and the magnetic field is pointed to the top of the screen. What is the direction of the force of the magnetic field on the particle? a. toward the top of the screen. b. toward the bottom of the screen. c. toward the left edge of the screen. d. toward the right edge of the screen. e. out of the screen. f. into the screen.

E

The point P lies along the perpendicular bisector of the line connecting two long straight wires S and T that are perpendicular to the page. A set of directions A through H is shown next to the diagram. When the two equal currents in the wires are directed up out of the page, the direction of the magnetic field at P is closest to the direction of a. E. b. F. c. G. d. H. e. A

E

For each statement below, select weather that statement describes an electric field, a magnetic field, both and electric and a magnetic field, or neither. (Note each answer is used once.) The field exerts a force on stationary charges. The field exerts a force on moving charges only. The force is proportional to the magnitude of the field exerting it. The magnitude of the force depends on the type (+ or - : North or south).

Electric Field Magnetic Field Both an electric and a magnetic field Neither an electric nor a magnetic field