Ch. 21 Flashcards
Suppose that you accidentally use your left hand, instead of your right hand, to determine the direction of the magnetic force that acts on a positive charge moving in a magnetic field. Do you get the correct answer?
No, because the direction you get will be opposite the correct direction.
A charged particle, passing through a certain region of space, has a velocity whose magnitude and direction remain constant.
If it is known that the external magnetic field is zero everywhere in this region, can you conclude that the external electric field is zero?
Yes
A charged particle, passing through a certain region of space, has a velocity whose magnitude and direction remain constant.
If it is known that the external electric field is zero everywhere, can you conclude that the external magnetic field is also zero?
No, because the particle could move either parallel or antiparallel to the magnetic field.
Suppose that a positive charge was launched from the negative plate toward the positive plate, in a direction opposite to the electric field E. A sufficiently strong electric field would prevent the charge from striking the positive plate. Suppose that the positive charge was launched from the South Pole toward the North Pole, in a direction opposite to the magnetic field B. Would a sufficiently strong magnetic field prevent the charge from reaching the North Pole?
No, because a magnetic field cannot exert a force on a charged particle that is moving antiparallel to the field.
A positive charge moves along a circular path under the influence of a magnetic field. The magnetic field is perpendicular to the plane of the circle. If the velocity of the particle is reversed at some point along the path, will the particle retrace its path?
No, because it will move around a different circle in a counterclockwise direction.
Assume that the particle in the picture is a proton. If an electron is projected at point 1 with the same velocity v, it will not follow exactly the same path as the proton, unless the magnetic field is adjusted in the following manner: the magnitude of the magnetic field must be ___, and the direction of the magnetic field must be ___.
Reduced, reversed
The drawing shows a conducting wire wound into a helical shape. The helix acts like a spring and expands back toward its original shape after the coils are squeezed together and released. The bottom end of the wire just barely touches the mercury (a good electrical conductor) in the cup. After the switch is closed, current in the circuit causes the light bulb to glow. The bulb…
Repeatedly turns on and off like a turn signal on a car
If the earths magnetism is assumed to originate from a large circular loop if current within the earth, then the plane of the current loop must be oriented ___ to the earths magnetic axis, and the direction of the current around the loop (when looking down on the loop from the North magnetic pole) is ___.
Perpendicular ; clockwise
The drawing shows an end-on view of three parallel wires that are perpendicular to the plane of the paper. In two of the wires the current is directed into the paper, while in the remaining wire the current is directed out of the paper. The two outermost wires are held rigidly in place. Which way will the middle wire move?
To the left.
There are four wires viewed end-on. They are long, straight, and perpendicular to the plane of the paper. Their cross sections lie at the corners of a square. The magnitude of the current in each wire is the same. What must be the direction of the current in each wire, so that when any single current is turned off, the total magnetic field in the center of the square is directed toward a corner of the square?
All into the page
In a TV commercial that advertises a soda pop, a strong electromagnet picks up a delivery truck carrying cans of the soft drink. The picture switches to the interior of the truck, where cans are seen to fly upward and stick to the roof just beneath the electromagnet. Are these cans made entirely of aluminum?
No, because aluminum is a non-ferromagnetic material.
Suppose that you have two bars. Bar 1 is a permanent magnet and Bar 2 is not a magnet, but is made from a ferromagnetic material like iron. A third bar (Bar 3), which is known to be a permanent magnet, is brought close to one end of Bar 1 and then to one end of Bar 2. Which one of the following statements are true?
Bars 1 and 3 will either be attracted to or repelled from each other, while bars 2 and 3 will always be attracted to each other.
At a location near the equator, the earths magnetic field is horizontal and points North. An electron is moving vertically upward from the ground. What is the direction of the magnetic force that acts on the electron?
East
The drawing shows the circular paths of an electron and a proton. These particles have the same charge magnitudes, but the proton is more massive. They travel at the same speed in a uniform magnetic field B, which is directed into the page everywhere. Which particle follows the larger circle, and does it travel clockwise or counterclockwise?
Proton; counterclockwise
A square, current-carrying loop is placed in a uniform magnetic field B with the plane of the loop parallel to the magnetic field. The dashed line is the axis of rotation. The magnetic field exerts ____.
A net torque, but not a net force, on the loop
