# EE AND ECE IMPORTANT MCQ-P.N JUNCTION DIODE

l.
The conventional current in a PN junction diode flows:

(a) From positive to negative
(b) From negative to positive
(c)
In the direction opposite to the electron flow.
(d) Both (a) and
(c) above

ANS-d
2.      The cut in voltage (or
knee voltage) of a silicon diode is                                                (a)
0.2V (b) 0.6V          (c) 0.8 V          (d)
l.0V
ANS-b
3.      When a diode is reverse
biased, it is equivalent to
(a) An OFF switch                 (b) an ON switch
(c) A high resistance            (d) none of the above
ANS-a
4.      The resistance of a
diode is equal to
(a) Ohmic resistance of the
P- and N- semiconductors
(b)
Junction resistance
(c) Reverse
resistance
(d)
Algebraic sum of (a) and (b) above

ANS-d
5.      For a silicon diode, the
value of the forward – bias voltage typically
(a) Must be greater than 0.3V
(b) Must be greater than 0.7V
(c) Depends on the width of the depletion
region
(d) Depends on the concentration of majority carriers

ANS-b
6.      When forward biased, a diode
(a) Blocks current                 (b)
conducts current
(c) Has a high resistance   (d) drops a large voltage.
ANS-b
7.      A PN junction diode’s
dynamic conductance is directly proportional to
(a) The applied
voltage         (b) the temperature

(c) The current                        (d) the thermal voltage

ANS-c

8. The forward region of a semiconductor diode characteristic curve
is where diode appears as

(a) Constant current
source        (b) a capacitor
(c) An OFF switch                          (d) an ON switch
ANS-d
9. At room temperature of 25 °C, the barrier potential for silicon
is 0.7 V. lts value at l25° C is
(a) 0.5V           (b) 0.3V           (c) 0.9V                 (d) 0.7V

ANS-a

l0.Junction breakdown of a PN junction
occurs

(a) With forward
bias                                (b)
with reverse bias
(c) Because of manufacturing defect  (d) None of these
ANS-b
11. Reverse saturation current in a silicon PN junction diode
nearly doubles for
every

(a) 2° C rise in temperature              (b) 5° C rise in temperature
(c) 6° C rise in temperature              (d) l0° C rise in temperature
ANS-d

l2.The
approximate value of v0  across the
diode shown in Fig below is

(a) Zero           (b) l0V             (c) 5V              (d) dependent on the value
of R
ANS-a

l3. The diode D is an ideal in the circuit
shown in Fig below. The current, I will be

(a) – 2nA         (b) zero           (c)
2 mA          (d) 4mA

ANS-c

l4. The voltage at Vl and V2 of the arrangement shown in Fig
below will be respectively

(a) 6V and 5.4V           (b) 5·4Vand 6V (c) 3V and 5·4V        (d) 6V and 5V

ANS-d

l5. The transition capacitance of a diode is l nF and it
can withstand a reverse potential of 400V. A capacitance of 2nF which can
withstand a reverse potential of l kV
is obtained by connecting

(a)   two
l nF diodes in series

(b)
six parallel branches with each branches comprising there l nF
diodes in series

(c)
two l
nF diodes in series

(d)
three parallel branches with each branch comprising lnF diodes
in series

ANS-b

l6.  A zener diode

(a)
has a high forward-voltage rating

(b)
has a sharp breakdown at low reverse voltage

(c)
is useful as an amplifier

(d)
has a negative resistance

ANS-b

l7.  A 5 V reference is drawn from the circuit
shown in Fig below if the zener diode current is of 5mA, then R will be

(a) 50fi            (b) 500 fi         (c) 5000 fi       (d)
50,000 fi