Chapter 29 Flashcards
(13 cards)
Consider the magnetic field due to the currentin the wire shown in the figure. Rank the points A, B , and C in terms of magnitude of the magnetic field that is due to the current in justthe length elelement ds shown from greatest toleast. (See figure)
B > C > A
A loose spiral spring carrying no current is hung from aceiling. When a switch is thrown so that a current existsin the spring, do the coils
(a) move closer together,
(b) move farther apart, or
(c) not move at all?
a
Consider a solenoid that is very long compared withits radius. Of the following choices, what is the mosteffective way to increase the magnetic field in theinterior of the solenoid?
(a) double its length, keeping the number of turns perunit length constant
(b) reduce its radius by half, keeping the number ofturns per unit length constant
(c) overwrap the entire solenoid with an additionallayer of current-carrying wire
c
What happens to the magnitude of the magnetic fieldinside a long solenoid if the radius is doubled?
1. It becomes four times larger.
2. It becomes twice as large.
3. It is unchanged.
4. It becomes one-half as large.
5. It becomes one-fourth as large.
3
Two long, parallel wires each carry the same current Iin the same direction (figure). The total magneticfield at the point P midway between the wires is:
1. zero.
2. directed into the page.
3. directed out of the page.
4. directed to the left.
5. directed to the right?
1
Two long, straight wires cross each other at a right angle, and each carriesthe same current I (figure). Which of the following statements is trueregarding the total magnetic field due to the two wires at the various pointsin the figure? More than one statement may be correct.
1. The field is strongest at points B and D.
2. The field is strongest at points A and C.
3. The field is out of the page at point B and into the page at point D.
4. The field is out of the page at point C and out of the page at point D.
5. The field has the same magnitude at all four points
1, 3
A long, straight wire carries a current I (figure). Which of the followingstatements is true regarding the magnetic field due to the wire? More thanone statement may be correct.
1. The magnitude is proportional to I/r, and the direction is out of thepage at P.
2. The magnitude is proportional to I/r2, and the direction is out of thepage at P.
3. The magnitude is proportional to I/r, and the direction is into thepage at P.
4. The magnitude is proportional to I/r2, and the direction is into thepage at P.
5. The magnitude is proportional to I, but does not depend on r.
1
Two long, parallel wires carrycurrents of 20.0 A and 10.0 A inopposite directions (figure). Whichof the following statements is true?More than one statement may becorrect.
1. In region I, the magnetic field is into the page and isnever zero.
2. In region II, the field is into the page and can be zero.
3. In region III, it is possible for the field to be zero.
4. In region I, the magnetic field is out of the page and isnever zero.5. There are no points where the field is zero.
3,4
Consider the two parallel wires carrying currents inopposite directions in the figure. Due to the magneticinteraction between the wires, the lower wireexperiences a magnetic force that is:
1. upward.
2. downward.
3. to the left.
4. to the right.
5. into the paper
2
What creates a magnetic field? More than one answermay be correct. Note: Later we will see that achanging electric field also creates a magnetic field.
1. a stationary object with electric charge
2. a moving object with electric charge
3. a stationary conductor carrying electric current
4. a difference in electric potential
5. an electric resistor
2, 3
A long solenoid with closely spaced turns carrieselectric current. Each turn of wire exerts:
1. an attractive force on the next adjacent turn.
2. a repulsive force on the next adjacent turn.
3. zero force on the next adjacent turn.
4. either an attractive or a repulsive force on thenext turn, depending on the direction of currentin the solenoid.
1
A uniform magnetic field is directed along the x axis.For what orientation of a flat, rectangular coil is theflux through the rectangle a maximum?
1. It is a maximum in the xy plane.
2. It is a maximum in the xz plane.
3. It is a maximum in the yz plane.
4. The flux has the same nonzero value for all theseorientations.
5. The flux is zero in all cases.
3
Solenoid A has length L and N turns, solenoid B haslength 2L and N turns, and solenoid C has length L/2and 2N turns. If each solenoid carries the samecurrent, rank the magnitudes of the magnetic fields inthe centers of the solenoids from largest to smallest.
1. C > A > B
2. A > B > C
3. B > C > A
1
