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WorksheetsELECS 38
Total questions: 50
Worksheet time: 25mins
When does maximum power transfer happen from the source to the load?
When the source resistance is greater than the load resistance
When the source resistance is less than the load resistance
When there is negligible source resistance
When the source resistance equals the load resistance
A transformer is plugged into a 120 V rms source and has a primary current of 300 mA rms. The secondary is providing 18 V across a 10Ω load. What is the efficiency of the transformer?
88%
90%
92%
95%
The coefficient of coupling between two coils is 0.45. The first coil has an inductance of 75 mH and the second coil has an inductance of 105 mH. What is the mutual inductance between the coils?
3.54 mH
7.88 mH
39.9 mH
189.3 mH
Increasing the number of turns of wire on the secondary of a transformer will
increase the secondary current
decrease the secondary current
have no effect on the secondary current
increase the primary current
What is the turns ratio of the transformer needed to match a 1 kΩ source resistance to a 160Ω load?
2.5:1
0.4:1
6.25:1
16:1
What is the secondary voltage in the given circuit?
13.3 V rms in phase with the primary
120 V rms in phase with the primary
13.3 V rms out of phase with the primary
120 V rms out of phase with the primary
The transformer turns ratio determines
the ratio of primary and secondary voltages
the ratio of primary and secondary currents
the reflected impedance
all of the above
Mutual induction is dependent on
winding ratios
output polarities
dc voltage levels
current changes
What is the current through the load in the given circuit?
500 μA
10 mA
250 mA
1.25 A
What is the power dissipated in the primary of the transformer in the given circuit?
25 mW
500 mW
12.5 W
62.5 W
A special transformer used to convert unbalanced signals to balanced signals is the
balun
autotransformer
center-tapped transformer
step-across transformer
If the load doubled in value in the given circuit, what reflected resistance would the source see?
80 Ω
400 Ω
2 kΩ
10 kΩ
If the primary power of an ideal transformer having a 2:1 voltage ratio is 100 W, the secondary power is
100 W
50 W
75 W
200 W
A transformer has
primary and secondary windings, both of which are considered inputs
primary and secondary windings, both of which are considered outputs
a primary winding used as an output and a secondary winding used as an input
a primary winding used as an input and a secondary winding used as an output
The primary function of the bias circuit is to
hold the circuit stable at VCC
hold the circuit stable at vin
ensure proper gain is achieved
hold the circuit stable at the designed Q-point
A JFET
is a current-controlled device
has a low input resistance
is a voltage-controlled device
is always forward-biased
A source follower has a voltage gain (Av) of
AV = gmRd
AV = gmRS
AV=gmRs / (1+gmRs)
AV=gmRd / (1+gmRd)
The capacitor that produces an ac ground is called a(n)
coupling capacitor
dc open
bypass capacitor
ac open
The formula used to calculate the approximate ac resistance of the base-emitter diode (re) is
re ≅ 25 mV / IE
re ≅ 25 mV x Ic
re ≅ 25 mV / IB
re ≅ 25 mV / Ic
The signal voltage gain of an amplifier, Av, is defined as:
Av = Vin / Vout
Av = Ic x Rc
Av ≅ Rc / RE
Av = Rc / RL
In a class B push-pull amplifier, the transistors are biased slightly above cutoff to avoid
crossover distortion
unusually high efficiency
negative feedback
a low input impedance
The depletion-mode MOSFET
can operate with only positive gate voltages
can operate with only negative gate voltage
cannot operate in the ohmic region
can operate with positive as well as negative gate voltages
Three different points are shown on a dc load line. The upper point represents the
minimum current gain
quiescent point
saturation point
cutoff point
Which of the following conditions are needed to properly bias an npn transistor amplifier?
Forward bias the base/emitter junction and reverse bias the base/collector junction.
Forward bias the collector/base junction and reverse bias the emitter/base junction.
Apply a positive voltage on the n-type material and a negative voltage on the p-type material.
Apply a large voltage on the base.
Often a common-collector will be the last stage before the load; the main function of this stage is to
provide voltage gain
buffer the voltage amplifiers from the low-resistance load
provide phase inversion
provide a high-frequency path to improve the frequency response
In order for feedback oscillators to have any practical value, the gain has to be
< 1
self-adjusting
stabilized
nonlinear
To get a negative gate-source voltage in a self-biased JFET circuit, you must use a
voltage divider
source resistor
ground
negative gate supply voltage
Intrinsic semiconductor material is characterized by a valence shell of how many electrons?
1
2
4
6
Ionization within a P-N junction causes a layer on each side of the barrier called the:
junction
depletion region
barrier voltage
forward voltage
What is the most significant development in electronics since World War II?
the development of color TV
the development of the diode
the development of the transistor
the development of the TRIAC
What causes the depletion region?
doping
diffusion
barrier potential
ions
What is an energy gap?
the space between two orbital shells
the energy equal to the energy acquired by an electron passing a 1 V electric field
the energy band in which electrons can move freely
an energy level at which an electron can exist
Silicon atoms combine into an orderly pattern called a:
covalent bond
crystal
semiconductor
valence orbit
In "n" type material, majority carriers would be:
holes
dopants
slower
electrons
Elements with 1, 2, or 3 valence electrons usually make excellent:
conductors
semiconductors
insulators
neutral
A commonly used pentavalent material is:
arsenic
boron
gallium
neon
Which material may also be considered a semiconductor element?
carbon
ceramic
mica
argon
In "p" type material, minority carriers would be:
holes
dopants
slower
electrons
\What can a semiconductor sense?
magnetism
temperature
pressure
all of the above
When an electron jumps from the valence shell to the conduction band, it leaves a gap. What is this gap called?
energy gap
hole
electron-hole pair
recombination
Forward bias of a silicon P-N junction will produce a barrier voltage of approximately how many volts?
0.2
0.3
0.7
0.8
Which semiconductor material is made from coal ash?
germanium
silicon
tin
carbon
When and who discovered that more than one transistor could be constructed on a single piece of semiconductor material:
1949, William Schockley
1955, Walter Bratten
1959, Robert Noyce
1960, John Bardeen
When is a P-N junction formed?
in a depletion region
in a large reverse biased region
the point at which two opposite doped materials come together
whenever there is a forward voltage drop
A P-N junction mimics a closed switch when it:
has a low junction resistance
is reverse biased
cannot overcome its barrier voltage
has a wide depletion region
Solid state devices were first manufactured during:
World War 2
1904
1907
1960
Electron pair bonding occurs when atoms:
lack electrons
share holes
lack holes
share electrons
How many valence electrons are in every semiconductor material?
1
2
3
4
What is a type of doping material?
extrinsic semiconductor material
pentavalent material
n-type semiconductor
majority carriers
Minority carriers are many times activated by:
heat
pressure
dopants
forward bias
