Electronics 133 chap 18,19,20
Inductive reactance is measured in
ohms
The combined reactance of parallel reactances is calculated by
the reciprocal formula
An induced voltage across a coil is actually the result of inducing electrons to move in a conductor; however there is no induced current. (t/f)
False
In a series circuit containing two inductors and a voltage source, the current is less in the inductor with the higher inductance. (t/f)
False
Inductors are not reactive components like capacitors. (t/f)
False
The base unit for inductance is
Henry
How is mutual inductance affected when primary and secondary inductances are increased and coupling is made tighter?
INCECREASE
What is the phase relationship between I R and V A in a parallel RL circuit?
IR is in phase with VA
An inductance can have X L to reduce the amount of alternating current because self-induced voltage is produced to oppose the applied voltage. (t/f)
True
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. (t/f)
True
Since reactance is an opposition in ohms, the values X L in series or parallel are combined the same way as ohms of resistance. (t/f)
True
The higher the frequency of the alternating current, and the greater the inductance, the X L opposition will be increased. (t/f)
True
What is the phase angle for the voltage across X L with respect to the current through L?
V L leads I L by 90°
The unit of apparent power is
Volt-amps
The combined parallel inductive reactance branch will be
less than the lowest branch reactance
The ability of one coil to induce a voltage in another coil nearby is referred to as
mutual inductance
A measure that indicates the relationship between the real and apparent power values is the
power factor
The process of adding a capacitor across the AC line to offset the effects of the inductive loads is
power factor correction
A trigonometric function of any angle of a right triangle, equal to the ratio of the opposite side to the adjacent side of a triangle is the
tanget
When alternating current flows in an inductance
the current is less than the dc resistance alone would allow
The values of X L in series or in parallel are combined
the same way as ohms of resistance
The amount of current in an ac circuit with only inductive reactance is equal to the applied voltage divided by the inductance. (t/f)
False
Real power is calculated using the expression:
P = I 2R
In a coil, the ratio of the reactive power in the inductance to the real power dissipated in the resistance is the
Q of the coil
The unit of reactive power is the
VAR
For a series RL circuit, when R is much larger than X L
Z T is approximately equal to R
The ratio of the number of turns in the primary to the number in the secondary is the
turns ratio
What is the inductive reactance for steady direct current?
0 Ω
The ideal condition of most power circuits is a power factor of
1
Frequency is equal to
1/T
How much is Z T for a 100 Ω R in series with a 100 Ω inductor?
141 Ω
X L equals
2πfL
With an inductive circuit, the phase angle between v L and i L is
90°
Power that is assumed to be consumed by the circuit is
apparent power
The amount of power the transformer can deliver to a resistive load is called
apparent power
Which of the following is not an example of how X L is generally used?
block dc
An inductance in series with an external resistance used to prevent the ac signal voltage from developing any appreciable output across the resistance at the frequency of the source is called a(n)
choke
The fraction of total flux from one coil linking another coil is the
coefficient of coupling
The factors that make the effective resistance of a coil more than its dc resistance do not include which of the following?
counter emf
An advantage of using a transformer with a separate winding secondary is
electrical isolation
For two coils with mutual inductance, any magnetic lines that do not link the two coils result in
leakage flux
Mutual inductance is also called
Mutual coupling
Inductance equals
X L/2πf
One way to express impedance is with
a complex number
The unit of mutual inductance is the
henry
Inductance has the useful characteristic of providing more ohms of reactance at
higher frequencies
The resultant of the phasor addition of R and X L is
impedance
Inductive reactance will increase if
inductance is increased
The ratio of v L/i L specifies the
inductive reactance
If the internal resistance of a coil is low
its Q is high
When sine-wave variations of current produce an induced voltage, the current
lags its induced voltage by 90°
To minimize transformer core losses while maintaining high flux density, the core can be made of
laminated steel