Magnetism and Electromagnetic Induction Section A 21-40

. For the four identical current-carrying wires shown (with conventional current coming out of the plane of the page), the wire on the right is labeled P. What is the direction of the total magnetic force on the wire labeled P that is caused by the other wires? A) To the left B) To the right C) Towards the top of the page D) There is no force.

A) to the left

A wire has a conventional current I directed to the right. At the instant shown in the figure, an electron has a velocity directed to the left. The magnetic force on the electron at this instant is

A) directed toward the top of the page. B) directed toward the bottom of the page. C) directed out of the plane of the page. D) directed into the plane of the page.

B) directed toward the bottom of the page.

An electron moves in the plane of the page through two regions of space along the dotted-line trajectory shown in the figure. There is a uniform electric field in Region I directed into the plane of the page (as shown). There is no electric field in Region II. What is a necessary direction of the magnetic field in regions I and II? Ignore gravitational forces.

A) Toward bottom of page Up on the page B) Toward top of page Into the page C) Toward top of page Out of the page D) Toward bottom of page Out of the page

C) Region I: Toward top of page Region II: Out of the page

A proton moves toward the top of this page into a region that has a magnetic field directed to the right of this page. If the particle is undeflected as it passes through this region, in what direction must there be a component of electric field? Ignore gravity.

A) To the left B) Into the page C) Out of the page D) To the right

C) Out of the page

For the figure shown, the variable resistance in the circuit is increased at a constant rate. What is the direction of the magnetic field at the point P at the center of the circuit

Magnetic Field at P A) Into the page B) Out of the page C) To the left D) There is no field

A) Into the page

A wire in the plane of the page carries a current directed toward the top of the page as shown. If the wire is located in a uniform magnetic field B directed out of the page, the force on the wire resulting from the magnetic field is (A) directed to the left (B) directed out of the page (C) directed to the right (D) zero

(C) directed to the right

The direction of the magnetic field at point R caused by the current I in the wire shown is (A) to the left (B) to the right (C) into the page (D) out of the page

(D) out of the page

Two long, parallel wires are separated by a distance d, as shown. One wire carries a steady current I into the plane of the page while the other wire carries a steady current I out of the page. At what points in the plane of the page and outside the wires, besides points at infinity, is the magnetic field due to the currents zero? (A) Only at point P (B) At all points on the line SS' (C) At all points on the line connecting the two wires (D) At no points

(D) At no points

. An electron is in a uniform magnetic field B that is directed out of the plane of the page, as shown. When the electron is moving in the plane of the page in the direction indicated by the arrow, the force on the electron is directed (A) toward the right (B) out of the page (C) into the page (D) toward the top of the page

(A) toward the right

. A metal spring has its ends attached so that it forms a circle. It is placed in a uniform magnetic field, as shown. Which of the following will not cause a current to be induced in the spring? (A) Changing the magnitude of the magnetic field (B) Rotating the spring about a diameter (C) Moving the spring parallel to the magnetic field (D) Moving the spring in and out of the magnetic field

(C) Moving the spring parallel to the magnetic field

A magnetic field of 0.1T forces a proton beam of 1.5 mA to move in a circle of radius 0.1 m. The plane of the circle is perpendicular to the magnetic field.

Of the following, which is the best estimate of the work done by the magnetic field on the protons during one complete orbit of the circle? (A) 0 J (B) 10-22 J (C) 10-5 J (D) 102

(A) 0 J

Of the following, which is the best estimate of the speed of a proton in the beam as it moves in the circle? (A) 10-2 m/s (B) 103 m/s (C) 106 m/s (D) 108 m/s

C) 106 m/s

Two parallel wires, each carrying a current I, repel each other with a force F. If both currents are doubled, the force of repulsion is (B) 2√2 F (C) 4F (C) 4√2 F (E) 8F

(C) 4√2 F

An electron e and a proton p are simultaneously released from rest in a uniform electric field E, as shown. Assume that the particles are sufficiently far apart so that the only force acting on each particle after it is released is that due to the electric field. At a later time when the particles are still in the field, the electron and the proton will have the same (A) speed (B) displacement (C) magnitude of acceleration (D) magnitude of force acting on them

(D) magnitude of force acting on them

Two long, parallel wires, fixed in space, carry currents I1 and I2. The force of attraction has magnitude F. What currents will give an attractive force of magnitude 4F? (A) 2I1 and ½I2 (B) ½I1 and ½I2 (C) 2I1 and 2I2 (D) 4I1 and 4I2

(C) 2I1 and 2I2

A charged particle is projected with its initial velocity parallel to a uniform magnetic field. The resulting path is (A) a spiral (B) a circular arc (C) a straight line parallel to the field (D) a straight line perpendicular to the field

(C) a straight line parallel to the field

Two very long parallel wires carry equal currents in the same direction into the page, as shown. At point P, which is 10 centimeters from each wire, the magnetic field is A) zero B) directed into the page C) directed out of the page D) directed to the right

D) directed to the right

A proton traveling with speed v enters a uniform electric field of magnitude E, directed parallel to the plane of the page, as shown in the figure. There is also a magnetic force on the proton that is in the direction opposite to that of the electric force. 38. Which of the following is a possible direction for the magnetic field?

D) directed out of the page (circle with dot inside)

If e represents the magnitude of the proton charge, what minimum magnitude of the magnetic field could balance the electric force on the proton? (A) E/v (B) eE/v (C) vE (D) eE

(A) E/v

A negatively charged particle in a uniform magnetic field B moves with constant speed v in a circular path of radius r, as shown. Which of the following graphs best represents the radius r as a function of the magnitude of B, if the speed v is constant?

B) graph with the L curve