Ac ch 19

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

Magnetic flux

A coil has some ______________ between windings.

Capacitance

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

Choke

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

C. 120 Hz

The fraction of total flux from one coil linking another coil is the _______________________.

Coefficient of coupling

Which of the following is a transformer core loss? A. Wire loss B. Dc-current loss C. Skin-effect current loss D. Hysteresis loss

D. Hysteresis loss

Which of the following is not an advantage of using an autotransformer? A. Compact B. Efficient C. Cost less D. Provide electrical isolation

D. Provide electrical isolation

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

Eddy current

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

Electrical isolation

With zero losses assumed for the transformer, the power in the secondary is __________ to the power in the primary.

Equal

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

False

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

False

The base unit for inductance is the ___________

Henry

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

Transformer

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.

True

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

True

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

Turns ratio

The unit of apparent power is ______________.

Volt Amperes

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

Apparent power

Counter emf or back emf is also known as a __________voltage.

Bucking

Induced voltage is the result of flux cutting across a_______________.

Conductor

Mutual inductance is also called mutual____________.

Coupling

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

False

Inductance is the characteristic that opposes any change in current.

False

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

Henry

The unit of mutual inductance is the __________.

Henry

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

Higher

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? ____________________

Impedance matching

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

Increases

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

Inductance

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

Inductance

The ability of one coil to induce a voltage in another coil nearby is referred to as _______________

Mutual inductance

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

Open

A high value of coefficient coupling is called ______________ coupling.

Tight

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

µH

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

Air core

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

Auto Transformer

The dc resistance between the primary and secondary windings of a transformer should always measure __________.

Infinity ohms

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

Laminated steel

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

Leakage flux

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

Reflected impedance

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

Self inductance

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

Self-inductance

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

Wire

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

four