Chapter 31 Flashcards
(10 cards)
You are performing an experiment that requires thehighest-possible magnetic energy density in the interiorof a very long current-carrying solenoid. Which of thefollowing adjustments increases the energy density?(More than one choice may be correct.)
(a) increasing the number of turns per unit length on thesolenoid
(b) increasing the cross-sectional area of the solenoid(
c) increasing only the length of the solenoid whilekeeping the number of turns per unit length fixed(
d) increasing the current in the solenoid
d & a
n the figure, coil 1 is moved closer to coil 2, with theorientation of both coils remaining fixed. Because ofthis movement, the mutual induction of the two coils
(a) increases,
(b) decreases, or
(c) is unaffected
a
At an instant of time during the oscillations of an LCcircuit, the current is at its maximum value. At thisinstant, what happens to the voltage across thecapacitor?
(a) It is different from that across the inductor.
(b) It is zero.
(c) It has its maximum value.
(d) It is impossible to determine
b
Now consider an instant when the current ismomentarily zero. Describe the magnitude of thevoltage across the capacitor at this instant.
(a) It is different from that across the inductor.
(b) It is zero.
(c) It has its maximum value.
(d) It is impossible to determine.
c
The centers of two circular loops are separated by afixed distance. For what relative orientation of theloops is their mutual inductance a maximum
1. coaxial and lying in parallel planes
2. lying in the same plane
3. lying in perpendicular planes, with the center ofone on the axis of the other
4. The orientation makes no difference.
1
The centers of two circular loops are separated by afixed distance. For what relative orientation is theirmutual inductance a minimum?
1. coaxial and lying in parallel planes
2. lying in the same plane
3. lying in perpendicular planes, with the center ofone on the axis of the other
4. The orientation makes no difference.
3
A solenoidal inductor for a printed circuit board is beingredesigned. To save weight, the number of turns isreduced by one-half, with the geometric dimensions keptthe same. By how much must the current change if theenergy stored in the inductor is to remain the same?
1. It must be four times larger.
2. It must be two times larger.
3. It should be left the same.
4. It should be one-half as large.5. No change in the current can compensate for thereduction in the number of turns
2
Two solenoids, A and B, are wound using equal lengthsof the same kind of wire. The length of the axis of eachsolenoid is large compared with its diameter. The axiallength of A is twice as large as that of B, and A has twiceas many turns as B. What is the ratio of the inductanceof solenoid A to that of solenoid B?
1. 4
2. 2
3. 1
4. 1/2
5. 1/4
4
If the current in an inductor is doubled, by what factoris the stored energy multiplied?
1. 4
2. 2
3. 1
4. 1/2
5. 1/4
1
Initially, an inductor with no resistance carries aconstant current. Then the current is brought to a newconstant value twice as large. After this change, whenthe current is constant at its higher value, what hashappened to the emf in the inductor?
1. It is larger than before the change by a factor of 4.
2. It is larger by a factor of 2.
3. It has the same nonzero value.
4. It continues to be zero.
5. It has decreased
4
