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MCQ
2561. Process of adding impurities to semiconductor is called-
mixing
refining
diffusing
doping
ব্যাখ্যা: The process of adding controlled inpurities to a semiconductor is known as "doping" The amount of impurity, or dopant, added to as intrinsic (pure) semiconductor varies its level of conductivity.
2562. The arrow in the symbol of a transistor indicates the direction of-
electron current in the emitter.
electron current in the collector.
hole current in the emitter.
donor ion current.
ব্যাখ্যাঃ The arrow in the symbol of transistor indicates the direction of hole current in the emitter.
2563. The maximum efficiency of a half-wave diode rectifier is --
50%
25%
40.0%
81.2%
2564. What is the full name of LCD?
Light control diode .
Light crystal display.
Liquid crystal diode.
Liquid crystal display.
2565. The energy band in which free electrons exist is--
first band
conduction band
second band
valence band
ব্যাখ্যা: The electrons occupying this band are called conduction electrons and the band is called the conduction band this band may be empty or partially filled. In this band, electrons move freely.
2566. A pn junction acts as a-
unidirectional switch.
bidirecctional switch.
controlled switch.
both unidirectional and bidirectional.
ব্যাখ্যা : The PN junction is conduct with forward bias only. It means they conduct in only one direction (Current flows from P to N). That's why PN Junction acts as unidirectional switch.
2567. Half-wave rectifier- maximum efficiency--%
25
50
40.6
81.2
2568. At what relgon a transistor operates --
Artlive
Saturatioit
Cut off
None
2569. When there is no forbidden region between the conductance band and valence band, the substance is called:
Semiconductor.
conductor
superconductor
insulator
2570. If, line frequency is 50 Hz, then output (Hz) of a bridge rectifier is-
25
100
50
None
ব্যাখ্যা: Output frequency of bridge rectifier is twice the input frequency. Full wave bridge rectifier, 25,2x50=100H
2571. If a power supply has no-load and full-load voltages of 30V and 25V respectively, then the percentage voltage regulation is:
10%
20%
15%
25%
2572. In an LC oscillator, the frequency of oscillation is:
Proportional to LC
Proportional to square root of LC
Inversely proportional to the square root of LC
Independent of the value of LC
2573. 2B. If PIV rating of a diode is exceeded-
the diode stops conduction.
the diode is destroyed.
the diode conducts heavily in the forward direction.
nothing happens.
ব্যাখ্যাঃ It is the peak inverse voltage rating (PIV) of a diode. When the voltage applied to a doide is more than PIV, it is likely to result in breakdown at the junction and the diodes gets destroyed.
2574. Class-B power amplifier- miximum collector efficiency কত %
25
78.5
50
60
2575. Emitter follower is used for--
Impedance matching
Current gain
Voltage gain
None of the above
2576. Which one is the smallest region in a transistor?
base
collector
emitter
both (a) and (b)
ব্যাখ্যা: The base region of a BJT transistor is very thin and is lightly doped with current carries. It is the region of a transistor which has opposite polarity charge carries from the emitter and the collector regions.
2577. At absolute zero temperanre (-273°C), an intrinsic semiconductor has-
a few free electrons.
many holes.
many free electrons.
no holes or free electrons.
ব্যাখ্যা : At absolute zero temperature (-273°C), an intrinsic semiconductor has no holes or free electrons.
2578. The primary function of a centre-tapped transformer in a power supply is to-
step up the voltage.
step down the voltage.
cause the diodes conduct alternately.
may step up or step down the voltage.
ব্যাখ্যাঃ The primary function of a centre-tapped transformer in a power supply is to step down the voltage.
2579. When transistor is used as an amplifier, it is operated in the:
Cut off region
Saturation region
Active region
Both a and b
2580. An alternating current is converted to direct current by-
dynamo
rectifier
transformer
motor
ব্যাখ্যা: A rectifier is a device which converts ac (alternating current) to de (direct current) which flows in only one direction. This process is know as rectification.