BIPOLAR JUNCTION TRANSISTOR | NCERTBOOKSPDF.COM

Objective Questions

Short notes

Objective questions (Answers are given below)

The emitter of a transistor is generally doped
the heaviest because it
(a) has to dissipate maximum power
(b) has to supply the charge carriers
(c) is the first region of the transistor
(d) must possess low resistance.
For current working of an NPN bipolar junction
transistor, the different electrodes should have the
following polarities with respect to emitter.
(a) collector +ve, base –ve
(b) collector –ve, base + ve
(c) collector – ve, base –ve
(d) collector + ve, base +ve
Select the CORRECT alternative.
In a bipolar transistor
(a) emitter region is of low/high resistivity
matterial which is lightly/ heavily-doped.
(b) collector region is of lower/higher conductivity
than emitter region
(c) base region is of high/low resistivity
material which is only lightly/ heavily doped.
In a properly-biased NPN transistor, most of the
electrons from the emitter
(a) recombine with holes in the base
(b) recombine in the emitter itself
(c) pass through the base to the collector
(d) are stopped by the junction barrier.
The following relationships between α and β
are correct EXCEPT
(a) 1
β = α
−α (b) 1
α = β
−β
(c) 1
α = β
+β (d) 1 1
1
−α =
+β
The value of total collector current in a CB
circuit is
(a) IC = α IE (b) I C = α IE + ICO
(c) IC = α IE – ICO (d) IC = α IE .
In a junction transistor, the collector cut off
current ICBO reduces considerably by doping the
(a) emitter with high level of impurity
(b) emitter with low level of impurity
(c) collector with high level of impurity
(d) collector with low level of impurity
In a transistor amplifier, the reverse saturation
current ICO
(a) doubles for every 10°C rise in temperature
(b) doubles for every 1°C rise in temperature
(c) increases linearly with the temperature
(d) doubles for every 5°C rise in temperature
In the case of a bipolar transistor, α is
(a) positive and > 1

(b) positive and < 1 (c) negative and > 1
(d) negative and < 1.

The EBJ of a given transistor is forward- biased
and its CBJ reverse-biased. If the base current
is increased, then its
(a) IC will decrease
(b) VCE will increase
(c) IC will increase
(d) VCC will increase.
The collector characteristics of a CE – connected
transistor may be used to find its
(a) input resistance
(b) base current
(c) output resistance
(d) voltage gain.
Which of the following approximations is often
used in electronic circuits ?
(a) IC ≅ IE (b) IB ≅ IC
(c) IB ≅ IE (d) IE ≅ IB + IC
When a transistor is fully switched ON, it is said
to be
(a) shorted (b) saturated
(c) open (d) cut-off
If a change in base current does not change the
collector current, the transistor amplifier is said
to be
(a) saturated (b) cut-off
(c) critical (d) complemented.
When an NPN transistor is saturated, its VCE
(a) is zero and IC is zero
(b) is low and IC is high
(c) equals VCC and IC is zero
(d) equals VCC and IC is high.
When an NPN transistor is cut-off, its VCC
(a) equals VCC and IC is high
(b) equals VCC and IC is zero
(c) is low and IC is high
(d) is high and IC is low.
If, in a bipolar junction transistor, IB = 100 μA
and IC = 10 mA, in what range does the value of
its beta lie ?
(a) 0.1 to 1.0 (b) 1.01 to 10
(c) 10.1 to 100 (d) 100.1 to 1000.
In a BJT, largest current flow occurs
(a) in the emitter (b) in the collector
(c) in the base
(d) through CB junction.
In a properly-connected BJT, an increase in base
current causes increase in
(a) IC only (b) IE only
(c) both IC and IE (d) leakage current

When a BJT operates in cut-off
(a) VCE = 0
(b) VCE =Vcc
(c) VCE has negative value
(d) IC is maximum.
When a BJT is in saturation
(a) IC = 0
(b) IB controls IC
(c) VCE = 0
(d) VCE has positive value.

(a) 2. (d) 3. (a) low, heavily (b) lower (c) high, lightly 4. (c) 5. (b) 6. (b) 7. (d) 8.(a) 9. (d) 10. (c) 11. (c) 12. (a) 13. (b) 14. (a) 15. (b) 16. (b) 17. (b) 18. (a) 19.(c) 20. (b) 21. (c)

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