Deck 20: Inductance

Question 1

A coil has some ______________ between windings.

Answer 1

capacitance

Question 2

______________-wound resistors have enough inductance to be evident at radio frequencies.

Answer 2

Wire

Question 3

When it is necessary to measure the value of an inductor, a ______________ analyzer should be used.

Answer 3

capacitor-inductor

Question 4

The most common trouble in coils is a(n) ______________ winding.

Question 5

______________ is the ability of a conductor to produce voltage when the current varies.

Question 6

The symbol for inductance is L, and the unit is the ______________.

Question 7

______________ coils are used in rf circuits because higher frequencies need less inductance for the required inductive effect.

Question 8

The ability of a conductor to induce voltage in itself when the current changes is its ______________.

Question 9

A high value of coefficient coupling is called ______________ coupling.

Question 10

With a(n) ______________ the secondary is not electrically isolated.

Question 11

What law or theorem states that the reaction v_L opposes its cause, which is the change in I?

A) Kirchhoff
B) Lenz
C) Thevenin
D) Ohm

Question 12

For two coils with mutual inductance, any magnetic lines that do not link the two coils result in

A) shielded coil inductance
B) non-mutual flux
C) leakage flux
D) magnetic misfire

Question 13

Mutual inductance is also called

A) mutual coupling
B) flux coupling
C) link coupling
D) inductive linking

Question 14

How is mutual inductance affected when primary and secondary inductances are increased and coupling is made tighter?

A) Increases
B) Decreases
C) Remains unchanged
D) Drops to zero

Question 15

What is the mutual inductance for two 400-mH coils L₁ and L₂ that have a coefficient of coupling of 0.3?

A) 80 mH
B) 12 mH
C) 120 mH
D) 1.2 H

Question 16

What component uses mutual inductance to step up or step down an alternating voltage?

A) Inductor
B) Capacitor
C) Resistor
D) Transformer

Question 17

The ratio of the number of turns in the primary to the number in the secondary is the

A) transformer ratio
B) coupling coefficient
C) coupling ratio
D) turns ratio

Question 18

When the secondary of a transformer has more turns than the primary, the secondary voltage is

A) higher than the primary
B) less than the primary
C) equal to the primary
D) considered loaded

Question 19

With zero losses assumed for the transformer, the power in the secondary

A) is always more than the primary
B) is always less than the primary
C) is equal to the power in the primary
D) is equal to I_S times R_S

Question 20

What is the primary current for a transformer with a 1:10 turns ratio that has 720 V across 7200 ? in the secondary?

A) 0.6 A
B) 0.1 A
C) 1.0 A
D) 1.0 mA

Question 21

Which of the following is not an advantage of using an autotransformer?

A) Compact
B) Efficient
C) Cost less
D) Provide electrical isolation

Question 22

An advantage of using a transformer with a separate winding secondary is

A) electrical isolation
B) dc can be coupled to the secondary
C) it is compact
D) it is inexpensive

Question 23

The amount of power the transformer can deliver to a resistive load is called

A) transformer power
B) actual power
C) apparent power
D) secondary power

Question 24

Which of the following is not a typical frequency rating for a power transformer?

A) 50 Hz
B) 60 Hz
C) 120 Hz
D) 400 Hz

Question 25

When a transformer is used to change or transform a secondary load impedance to a new value as seen by the primary, the secondary impedance is called

A) transformed impedance
B) reflected impedance
C) refracted impedance
D) revised impedance

Question 26

What is it called when a transformer is used to achieve maximum transfer of power from a generator to a load when the generator and load impedances are not the same?

A) Maximum power transfer
B) Power matching
C) Impedance matching
D) Maximum loading

Question 27

Which of the following is a transformer core loss?

A) Wire loss
B) Dc-current loss
C) Skin-effect current loss
D) Hysteresis loss

Question 28

What is a current that flows in a circular path through the cross section of a transformer core that results in a loss?

A) Wire current
B) Dc current
C) Ac current
D) Eddy current

Question 29

To minimize transformer core losses while maintaining high flux density, the core can be made of

A) copper
B) silver
C) laminated steel
D) mica

Question 30

What is a common piece of test equipment used to increase the ac voltage slowly while monitoring the operation of the equipment being repaired?

A) Function generator
B) Dc power supply
C) Variac
D) Signal generator

Question 31

Inductance is the ability of a conductor to produce induced voltage when the current varies.

Question 32

A coil has more inductance than the equivalent length of straight wire because the coil concentrates magnetic flux.

Question 33

The base unit for inductance is the gilbert.

Question 34

The rate of flux change is greatest when the alternating current passes through zero.

Question 35

Induced voltage is the result of flux cutting across an insulator.

Question 36

The ability of a conductor to induce voltage in itself when current changes is its self-inductance.

Question 37

One henry is the amount of inductance that allows one volt to be induced when the current changes at the rate of one ampere per second.

Question 38

Too much current flowing through a coil will increase its permeability and inductance.

Question 39

If the number of turns of a coil is doubled in the same area and length, the inductance is increased by four times.

Question 40

A steady dc current can induce a voltage in a coil.

Question 41

Air-core coils for rf applications have inductance values in mH and ?H.

Question 42

A typical air-core rf inductor is called a choke.

Question 43

An induced voltage across a coil is actually the result of inducing electrons to move in a conductor; however there is no induced current.

Question 44

Counter emf or back emf is also known as a bucking voltage.

Question 45

Inductance is the characteristic that opposes any change in voltage.