CHAPTER 10 : INDUCTANCE

Which of the following statements represents an advantage of a toroidal coil over a

solenoidal coil?

(a) You can easily permeability-tune a toroid but not a solenoid.

(b) A toroid can carry more current than a solenoid with the same gauge wire.

(c) A toroid can function with a ferromagnetic core, but a solenoid cannot.

(d) A toroid practically prevents unwanted mutual inductance, while solenoids allow it.

D

You connect four 44.0-mH toroidal inductors in parallel. They exhibit no mutual

inductance. What's the net inductance of the combination?

(a) 11.0 mH

(b) 22.0 mH

(c) 88.0 mH

(d) 176 mH

A

You connect two 44.0-mH solenoidal inductors in series. They exhibit no mutual

inductance. What's the net inductance of the combination?

(a) 22.0 mH

(b) 88.0 mH

(c) 176 mH

(d) 352 mH

B

Schematic 10.1

In Schematic 10-1, both inductors have values of 40 mH. Their magnetic fields oppose each

other. Some mutual inductance exists between them. The net inductance of the combination is

(a) less than 80 mH.

(b) exactly 80 mH.

(c) more than 80 mH.

(d) zero.

A

Schematic 10-2

In Schematic 10-2, both inductors have values of 40 μH. Their magnetic fields reinforce each

other. Some mutual inductance exists between them. The net inductance of the combination is

(a) less than 80 μH.

(b) exactly 80 μH.

(c) more than 80 μH.

(d) 160 μH.

C

To obtain the lowest possible inductance for a 100-turn coil, you should use

(a) an air-core solenoid.

(b) a powdered-iron-core solenoid.

(c) a pot-core coil.

(d) a powdered-iron-core toroid.

A

Which of the following factors affects the inductance of a pot-core coil, if all other factors

stay the same?

(a) The frequency of the applied signal

(b) The amplitude of the applied signal

(c) The wave shape of the applied signal

(d) The permeability of the core (shell) material

D

As the number of turns increases in an air-core coil, then its inductance, assuming all other

factors remain constant,

(a) increases.

(b) stays the same.

(c) decreases.

(d) approaches zero.

A

As you increase the amplitude of the AC signal that you apply to a toroidal coil, leaving all

other factors unchanged, the coil's inductance

(a) increases.

(b) stays the same.

(c) decreases.

(d) approaches zero.

B

To increase the inductance of a solenoidal coil without changing anything else, you can

increase the

(a) signal frequency.

(b) core permeability.

(c) signal strength.

(d) wire diameter.

B

You connect a 500-μH inductor coil in series with a 900-μH inductor coil, winding them

over each other so the coefficient of coupling is 1. Both coils are solenoids whose magnetic fields

reinforce each other. What's the mutual inductance between the coils?

(a) 1.40 mH

(b) 700 μH

(c) 671 μH

(d) More information is needed to calculate it.

C

What's the net (total) inductance of the above combination?

(a) 2.74 mH

(b) 2.04 mH

(c) 2.01 mH

(d) More information is needed to calculate it.

A

At which of the following frequencies would you most likely use an air-core solenoidal coil to

obtain useful inductance?

(a) 6 kHz

(b) 20 MHz

(c) 900 GHz

(d) Any of the above

B

You have two 50-turn, air-core, loop-like coils, each one measuring 2 centimeters in

diameter. You align their axes, place them far from one another, and then gradually bring them

closer together. What happens to the coefficient of coupling as you do this?

(a) It decreases.

(b) It stays the same.

(c) It increases.

(d) You'll need more information to answer this question.

C

What happens to the mutual inductance between the two coils as you carry out the exercise

described in Question 14 above?

(a) It decreases.

(b) It stays the same.

(c) It increases.

(d) You'll need more information to answer this question.

D

You have two 50-turn loop-like coils, each one measuring 2 centimeters in diameter. You

surround each coil with a pot-core shell, align their axes, place them far from one another, and then

gradually bring them closer together. What happens to the coefficient of coupling as you do this?

(a) It decreases.

(b) It stays the same.

(c) It increases.

(d) You'll need more information to answer this question.

B

What happens to the mutual inductance between the two coils as you carry out the exercise

described in Question 16 above?

(a) It decreases.

(b) It stays the same.

(c) It increases.

(d) You'll need more information to answer this question.

B

Consider a length of transmission line with its wires connected together at the far end. Suppose

that the line's velocity factor is 0.750, and you apply a signal at 100 MHz to the open (near)

end. To make this line measure . electrical wavelength, you must cut it to a physical length of

(a) 1.13 m.

(b) 79.5 cm.

(c) 56.3 cm.

(d) 23.1 cm.

C

If you decrease the frequency to 90 MHz in the situation described in Question 18 above but

don't change anything else, and if you keep the wires at the line's far end connected together, then

the signal source at the open (near) end will "see"

(a) a capacitance.

(b) a short circuit.

(c) an inductance.

(d) an open circuit.

C

If you increase the frequency to 230 MHz in the situation described in Question 18 but

don't change anything else, and if you keep the wires at the line's far end connected together, then

the signal source at the open (near) end will "see"

(a) a capacitance.

(b) a short circuit.

(c) an inductance.

(d) an open circuit.

C