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Practice Test - Dual Nature of matter, Atom-molecular nuclei, Semi-conductors & Communication Notes | EduRev

: Practice Test - Dual Nature of matter, Atom-molecular nuclei, Semi-conductors & Communication Notes | EduRev

``` Page 1

[1]

(Dual Nature of matter, Atom-molecular nuclei, Semi-conductors &
Communication)
1. An electron and a proton are injected into a
uniform electric field at right angle to the field
with the same kinetic energy. What is the nature
of their trajectories?
(a) Electron trajectory is more curved than the
proton trajectory
(b)  Electron trajectory is less curved than the
proton trajectory
(c) Both trajectories are equally curved
(d) Both trajectories are straight lines.
2. When a beam of accelerated electrons hits a target,
continuous X- ray spectrum is emitted from the
target. Which one of the following wavelength is
absent  in the X-rays tube is operated at 40,000 V?
(a) 1.5Å (b)  0.5 Å
(c) 0.25 Å (d) 1.0 Å
3. Ultraviolet radiation of 6.2 eV falls on an
aluminium surface (work function 4.2 eV). The
kinetic energy in joule of the fastest electron
emitted is approximately
(a) 3 × 10
-
21
(b)  3 × 10
-
19

(c) 3 × 10
-
17
(d) 3 × 10
-
15

4. T is the half life period and T
a
is the average life
of a radioactive substance. Which of the following
statement is correct ?
(a) T > T
a

(b)  T is about 69% of T
a
(c) T is inversely proportional to T
a

(d) T and T
a
both are directly proportional to
5. Bi has a half life of 5 days. What time is taken by
(7/8)th part of the sample to decay ?
(a) 3.4 days (b)  10 days
(c) 15 days (d) 20 days.
6. From the following equations pick out the
possible nuclear fusion reaction
(a) 6
C
13
+
1
H
1
?
6
C
14
+ 4.3 MeV
(b)
6
C
12
+
1
H
1
?
7
N
13
+ 2 MeV
(c)
7
N
14
+
1
H
1
?
8
O
16
+ 7.3 MeV
(d)
92
U
235
+
0
n
1
?
54
Xe
140
+
38
Sr
94
+ 2(
0
n
1
) + ? +
200 MeV
7. The stopping potential as a function of frequency
plotted for two
different photoelectric
surfaces A  and B. The
graphs shows that the
work function of A is
(a) greater than that
of B
(b) smaller than that of B
(c) same as that of B
(d) such that no comparison can be done from
given graphs
8. The minimum wavelength of X-rays produced by
accelerating potential V is ?. What will be the
minimum wavelength, when the accelerating
potential is 2 V.
(a) 2 ? (b) 2 ?
(c) ? 2 (d) ?/2
9. The relation between  half life T
1/2
sample and its mean life ? is
(a) T
1/2
= 0.693 t (b) t = 0.693 T
1/2

(c) t = T
1/2
(d) t = 2.718 T
1/2
10. According to Bohr’s theory the radius of electron
in an orbit described by principal quantum
number n and atomic number Z is proportional to
(a) Z
2
n
2
(b) Z
2
/n
2

(c) (Z
2
/n) (d) (n
2
/Z).
11. A transistor is preferable to triode valve because it
(a) can withstand larger changes in temperature
(b) has higher input impedance
(c) can handle larger powers
(d) does not require a heater
12. What is the value of A . A in Boolean algebra :
(a) 0 (b) 1
(c) A (d) A
13. When NPN transistor is used as an amplifier then
(a) electrons move from base to collector
(b) holes move from emitter to base
(c) electrons move from collector to base
(d) holes move from base to emitter
14. In p -type semiconductor :
(a) major current carriers are electrons
(b) major current carriers are mobile negative
ions
(c) major current carriers are mobile holes
(d) the number of mobile holes exceeds the
number of acceptors
15. The diffusion current in a P -N junction is :
(a) from n -side to p -side
(b) from p -side & n -side
(c) from n -side to p -side, if forward biased
(d) from p -side to n -side, if reverse biased
16. n -type germanium is obtained on doping intrinsic
germanium with :
Page 2

[1]

(Dual Nature of matter, Atom-molecular nuclei, Semi-conductors &
Communication)
1. An electron and a proton are injected into a
uniform electric field at right angle to the field
with the same kinetic energy. What is the nature
of their trajectories?
(a) Electron trajectory is more curved than the
proton trajectory
(b)  Electron trajectory is less curved than the
proton trajectory
(c) Both trajectories are equally curved
(d) Both trajectories are straight lines.
2. When a beam of accelerated electrons hits a target,
continuous X- ray spectrum is emitted from the
target. Which one of the following wavelength is
absent  in the X-rays tube is operated at 40,000 V?
(a) 1.5Å (b)  0.5 Å
(c) 0.25 Å (d) 1.0 Å
3. Ultraviolet radiation of 6.2 eV falls on an
aluminium surface (work function 4.2 eV). The
kinetic energy in joule of the fastest electron
emitted is approximately
(a) 3 × 10
-
21
(b)  3 × 10
-
19

(c) 3 × 10
-
17
(d) 3 × 10
-
15

4. T is the half life period and T
a
is the average life
of a radioactive substance. Which of the following
statement is correct ?
(a) T > T
a

(b)  T is about 69% of T
a
(c) T is inversely proportional to T
a

(d) T and T
a
both are directly proportional to
5. Bi has a half life of 5 days. What time is taken by
(7/8)th part of the sample to decay ?
(a) 3.4 days (b)  10 days
(c) 15 days (d) 20 days.
6. From the following equations pick out the
possible nuclear fusion reaction
(a) 6
C
13
+
1
H
1
?
6
C
14
+ 4.3 MeV
(b)
6
C
12
+
1
H
1
?
7
N
13
+ 2 MeV
(c)
7
N
14
+
1
H
1
?
8
O
16
+ 7.3 MeV
(d)
92
U
235
+
0
n
1
?
54
Xe
140
+
38
Sr
94
+ 2(
0
n
1
) + ? +
200 MeV
7. The stopping potential as a function of frequency
plotted for two
different photoelectric
surfaces A  and B. The
graphs shows that the
work function of A is
(a) greater than that
of B
(b) smaller than that of B
(c) same as that of B
(d) such that no comparison can be done from
given graphs
8. The minimum wavelength of X-rays produced by
accelerating potential V is ?. What will be the
minimum wavelength, when the accelerating
potential is 2 V.
(a) 2 ? (b) 2 ?
(c) ? 2 (d) ?/2
9. The relation between  half life T
1/2
sample and its mean life ? is
(a) T
1/2
= 0.693 t (b) t = 0.693 T
1/2

(c) t = T
1/2
(d) t = 2.718 T
1/2
10. According to Bohr’s theory the radius of electron
in an orbit described by principal quantum
number n and atomic number Z is proportional to
(a) Z
2
n
2
(b) Z
2
/n
2

(c) (Z
2
/n) (d) (n
2
/Z).
11. A transistor is preferable to triode valve because it
(a) can withstand larger changes in temperature
(b) has higher input impedance
(c) can handle larger powers
(d) does not require a heater
12. What is the value of A . A in Boolean algebra :
(a) 0 (b) 1
(c) A (d) A
13. When NPN transistor is used as an amplifier then
(a) electrons move from base to collector
(b) holes move from emitter to base
(c) electrons move from collector to base
(d) holes move from base to emitter
14. In p -type semiconductor :
(a) major current carriers are electrons
(b) major current carriers are mobile negative
ions
(c) major current carriers are mobile holes
(d) the number of mobile holes exceeds the
number of acceptors
15. The diffusion current in a P -N junction is :
(a) from n -side to p -side
(b) from p -side & n -side
(c) from n -side to p -side, if forward biased
(d) from p -side to n -side, if reverse biased
16. n -type germanium is obtained on doping intrinsic
germanium with :
[2]

(a) Phosphorus  (b) Aluminium
(c) Boron  (d) Gold
17. The band gap in germanium and silicon in eV
respectively is :
(a) 0.7, 1.1 (b) 1.1, 0.7
(c) 1.0,0 (d) 0, 1.1
18. An electron and a proton are injected into a
uniform magnetic field perpendicular to it with
the same momentum. What is the nature of their
trajectories ?
(a) Radius of curvature is less for electron
(b)  Radius of curvature is more for electron
(c) Radius of curvature is same for both
(d) Both move along straight lines.
19. The p–n junction diode works as insulator, if
connected
(a) to A.C.  (b) in forward bias
(c) in reverse bias  (d) none of these
20. the reverse process of pair production is called
(a) annihilation of matter
(b) a–decay
(d) carbon–nitrogen cycle
21. The least doped region in a transistor is
(a) emitter
(b) collector
(c) base
(d) either emitter or collector
22. Radiowave frequency 30 MHz to 300 MHz belong
to which of the following ?
(a) HF (b)  UHF
(c) VHF (d) SHF.
23. In which of the following cases the band width as
well as modutation increases ?
(a) DSB (b)  SSB
(c) AM (d) FM.
24. What is the range of frequency of microwaves :
(a) 3 × 10
12
to 3 × 10
9
Hz
(b) 3 × 10
11
to 1 × 10
9
Hz
(c) 3 × 10
10
to 3 × 10
9
Hz
(d) 3 × 10
9
to 1 × 10
9
Hz
25. Which of the following is not the mode of
transmission of radiowaves from one place to
another
(a) Ground wave  (b) Space wave
(c) Sky wave  (d) Carrier wave
In every question a statement of ASSERTION is
followed by a statement of REASON. Mark the
correct answer out of the following choices:
(a) If both ASSERTION and REASON are true
and reason is the correct explanation of the
assertion.
(b) If both ASSERTION and REASON are true
but reason is not the correct explanation of the
assertion.
(c) If ASSERTION is true but REASON is false.
(d) If ASSERTION is false but REASON is true.
26. Assertion: If electrons were not orbiting the
nucleus and were stationary, they would collapse
into the nucleus.
Reason: There is electrostatic attraction between
protons in the nucleus and the orbiting electrons.
27. Assertion: A spectral line is emitted when an
electron rotates in a fixed elliptical orbit.
Reason: The concept of elliptical orbits was put
forth by Sommerfeld.
28. Assertion : Thermionic emission from the surface
of a metal when it is heated to incandescence was
discovered by Thomas Edison.
Reason     : Thermions have negative charge.
29. Assertion : A diode can be used as a rectifier.
Reason     : Electrons are emitted by the cathode
and collected by the anode.
30. Assertion : In a semiconductor, the conduction
electrons have a higher mobility than holes.
Reason     : The electrons experience fewer
collisions.
Test-10 (Dual Nature of matter, Atom-molecular nuclei, Semi-conductors &
Communication)

1 C 6 B 11
D
16
A
21
C
26
B
2 C 7 B 12 A 17 A 22 C 27 D
3 B 8 D 13 A 18 C 23 D 28 B
4 B 9 A 14
C
19
C
24
B
29
A
5 C 10 D 15
B
20 A 25 D 30 C

Page 3

[1]

(Dual Nature of matter, Atom-molecular nuclei, Semi-conductors &
Communication)
1. An electron and a proton are injected into a
uniform electric field at right angle to the field
with the same kinetic energy. What is the nature
of their trajectories?
(a) Electron trajectory is more curved than the
proton trajectory
(b)  Electron trajectory is less curved than the
proton trajectory
(c) Both trajectories are equally curved
(d) Both trajectories are straight lines.
2. When a beam of accelerated electrons hits a target,
continuous X- ray spectrum is emitted from the
target. Which one of the following wavelength is
absent  in the X-rays tube is operated at 40,000 V?
(a) 1.5Å (b)  0.5 Å
(c) 0.25 Å (d) 1.0 Å
3. Ultraviolet radiation of 6.2 eV falls on an
aluminium surface (work function 4.2 eV). The
kinetic energy in joule of the fastest electron
emitted is approximately
(a) 3 × 10
-
21
(b)  3 × 10
-
19

(c) 3 × 10
-
17
(d) 3 × 10
-
15

4. T is the half life period and T
a
is the average life
of a radioactive substance. Which of the following
statement is correct ?
(a) T > T
a

(b)  T is about 69% of T
a
(c) T is inversely proportional to T
a

(d) T and T
a
both are directly proportional to
5. Bi has a half life of 5 days. What time is taken by
(7/8)th part of the sample to decay ?
(a) 3.4 days (b)  10 days
(c) 15 days (d) 20 days.
6. From the following equations pick out the
possible nuclear fusion reaction
(a) 6
C
13
+
1
H
1
?
6
C
14
+ 4.3 MeV
(b)
6
C
12
+
1
H
1
?
7
N
13
+ 2 MeV
(c)
7
N
14
+
1
H
1
?
8
O
16
+ 7.3 MeV
(d)
92
U
235
+
0
n
1
?
54
Xe
140
+
38
Sr
94
+ 2(
0
n
1
) + ? +
200 MeV
7. The stopping potential as a function of frequency
plotted for two
different photoelectric
surfaces A  and B. The
graphs shows that the
work function of A is
(a) greater than that
of B
(b) smaller than that of B
(c) same as that of B
(d) such that no comparison can be done from
given graphs
8. The minimum wavelength of X-rays produced by
accelerating potential V is ?. What will be the
minimum wavelength, when the accelerating
potential is 2 V.
(a) 2 ? (b) 2 ?
(c) ? 2 (d) ?/2
9. The relation between  half life T
1/2
sample and its mean life ? is
(a) T
1/2
= 0.693 t (b) t = 0.693 T
1/2

(c) t = T
1/2
(d) t = 2.718 T
1/2
10. According to Bohr’s theory the radius of electron
in an orbit described by principal quantum
number n and atomic number Z is proportional to
(a) Z
2
n
2
(b) Z
2
/n
2

(c) (Z
2
/n) (d) (n
2
/Z).
11. A transistor is preferable to triode valve because it
(a) can withstand larger changes in temperature
(b) has higher input impedance
(c) can handle larger powers
(d) does not require a heater
12. What is the value of A . A in Boolean algebra :
(a) 0 (b) 1
(c) A (d) A
13. When NPN transistor is used as an amplifier then
(a) electrons move from base to collector
(b) holes move from emitter to base
(c) electrons move from collector to base
(d) holes move from base to emitter
14. In p -type semiconductor :
(a) major current carriers are electrons
(b) major current carriers are mobile negative
ions
(c) major current carriers are mobile holes
(d) the number of mobile holes exceeds the
number of acceptors
15. The diffusion current in a P -N junction is :
(a) from n -side to p -side
(b) from p -side & n -side
(c) from n -side to p -side, if forward biased
(d) from p -side to n -side, if reverse biased
16. n -type germanium is obtained on doping intrinsic
germanium with :
[2]

(a) Phosphorus  (b) Aluminium
(c) Boron  (d) Gold
17. The band gap in germanium and silicon in eV
respectively is :
(a) 0.7, 1.1 (b) 1.1, 0.7
(c) 1.0,0 (d) 0, 1.1
18. An electron and a proton are injected into a
uniform magnetic field perpendicular to it with
the same momentum. What is the nature of their
trajectories ?
(a) Radius of curvature is less for electron
(b)  Radius of curvature is more for electron
(c) Radius of curvature is same for both
(d) Both move along straight lines.
19. The p–n junction diode works as insulator, if
connected
(a) to A.C.  (b) in forward bias
(c) in reverse bias  (d) none of these
20. the reverse process of pair production is called
(a) annihilation of matter
(b) a–decay
(d) carbon–nitrogen cycle
21. The least doped region in a transistor is
(a) emitter
(b) collector
(c) base
(d) either emitter or collector
22. Radiowave frequency 30 MHz to 300 MHz belong
to which of the following ?
(a) HF (b)  UHF
(c) VHF (d) SHF.
23. In which of the following cases the band width as
well as modutation increases ?
(a) DSB (b)  SSB
(c) AM (d) FM.
24. What is the range of frequency of microwaves :
(a) 3 × 10
12
to 3 × 10
9
Hz
(b) 3 × 10
11
to 1 × 10
9
Hz
(c) 3 × 10
10
to 3 × 10
9
Hz
(d) 3 × 10
9
to 1 × 10
9
Hz
25. Which of the following is not the mode of
transmission of radiowaves from one place to
another
(a) Ground wave  (b) Space wave
(c) Sky wave  (d) Carrier wave
In every question a statement of ASSERTION is
followed by a statement of REASON. Mark the
correct answer out of the following choices:
(a) If both ASSERTION and REASON are true
and reason is the correct explanation of the
assertion.
(b) If both ASSERTION and REASON are true
but reason is not the correct explanation of the
assertion.
(c) If ASSERTION is true but REASON is false.
(d) If ASSERTION is false but REASON is true.
26. Assertion: If electrons were not orbiting the
nucleus and were stationary, they would collapse
into the nucleus.
Reason: There is electrostatic attraction between
protons in the nucleus and the orbiting electrons.
27. Assertion: A spectral line is emitted when an
electron rotates in a fixed elliptical orbit.
Reason: The concept of elliptical orbits was put
forth by Sommerfeld.
28. Assertion : Thermionic emission from the surface
of a metal when it is heated to incandescence was
discovered by Thomas Edison.
Reason     : Thermions have negative charge.
29. Assertion : A diode can be used as a rectifier.
Reason     : Electrons are emitted by the cathode
and collected by the anode.
30. Assertion : In a semiconductor, the conduction
electrons have a higher mobility than holes.
Reason     : The electrons experience fewer
collisions.
Test-10 (Dual Nature of matter, Atom-molecular nuclei, Semi-conductors &
Communication)

1 C 6 B 11
D
16
A
21
C
26
B
2 C 7 B 12 A 17 A 22 C 27 D
3 B 8 D 13 A 18 C 23 D 28 B
4 B 9 A 14
C
19
C
24
B
29
A
5 C 10 D 15
B
20 A 25 D 30 C

[3]

SOLUTIONS

1. The path will be parabola given by : y =
2 2
2
x
) KE (
eE
4
1
x
mv
eE
2
1
= ; Since KE is same for both
particles, hence both trajectories are equally
curves.
2. Minimum wavelength = hc/eV.
3. E
k
= 6.2 - 4.2 = 2eV  = 2 × 1.6 × 10
-
19
J = 3.2 × 10
-
19

J
4. T = . T / 1 and
693 . 0
a
= ?
?
; Hence T = 0.693 T
a
.
5. A = A
0

n
2
1
?
?
?
?
?
?
, Here A = (1 - )
8
7
A
0
=
8
1
A
0
. Hence
8
1
A
0
= (A
0
)
n
2
1
?
?
?
?
?
?
. This gives n = 3, Hence t = 3 ×
5 = 15 days.
6. (b)
7. The intersect of the graph with v -axis gives
threshold frequency ? = hv
0
.
8. ?
min
= hc/eV.
9. It is factual relation.
10. r = ) Z / n (
me
h
2
4
2
0
p
e

11. Hence, efficiency is higher.
12. A. A = 0 both when A = 0 or 1.
13. Majority carriers in NPN transistor are electrons.
14. (c)
15. Positive charge carriers that is the holes diffuse
from a region of high concentration to regions of
lower concentration.
16. N -Type semiconductor is obtained by doping
with pentavalent impurities.
17. The forbidden band for germanium (Ge) and
silicon (Si) are 0.7 and 1.1 eV respectively.
18. (c).
19. (c)
20. (a)
21. (c)
22. (c)
23. (d)
24. (b)
25. (d)
26. (b) Both assertion and reason are true but reason
is not the correct explanation of the assertion.
Both the assertion and reason are true. The
assertion has stationary charges whereas the
reason has moving charges, therefore, the reason
cannot explain the assertion.
However, there is an electrostatic force between
the nucleus (positive charge) and the stationary
electrons (negative charge) of the atom. This
electrostatic force is one of attraction. If the
electrons were not orbiting the nucleus but were
free to move, this attractive force would draw
them towards the nucleus. As the distance would
go on decreasing the force of attraction would go
on increasing and the electron would finally fall
into the nucleus.
(Actually this does not happen as the electrons are
not stationary but move around the nucleus in
definite quantized orbits.)
27. (d) Assertion is false but reason is true.
A spectral line will be emitted by the electron only
when there is a change in its orbit i.e. when an
electron goes from a higher orbit to a lower orbit.
When the electron is in a fixed orbit it does not
Like the model of the solar system, Sommerfield
suggested that the orbits of the electron are not
perfect circles. They are elliptical. This helped in
removing some very fine discrepancies between
the observations and predictions based on perfect
circular orbits.
28. (b) Both assertion and reason are true but
reason is not the correct explanation of the
assertion:
The conduction -electrons/free -electrons are free
to move within the melt. They cannot leave the
surface due to attraction of positive ions. At
ordinary temperatures, the average kinetic energy
of the free electrons is insufficient to over come
the surface barrier when a water is heat the
average kinetic energy of free electrons also
increases, as the temperature rise. When the
electrons attain energy sufficient to overcome the
surface barrier, they escape from the metal. This
thermionic emission phenomenon was discovered
by Thomas Alva Edison. The assertion is correct.
Electrons emitted by heating of metals are called
thermions. Hence, thermions carry a negative
charge. The reason is correct. The reason does not
explain the thermionic emission.
29. (a) Both assertion and reason are true and
reason is the correct explanation of the assertion.
Electrons are emitted by the filament (cathode)
and collected by the plate (anode). The current
flows only in one direction from the plate to the
cathode when the plate is at a positive potential.
The reason is correct. This property of the diode,
of unidirectional current is utilized in rectifying
alternate current into a direct current. As long as
there  is a positive potential  on the plate, the
diode conducts but when the potential on the
plate becomes negative the flow of current stops.
Page 4

[1]

(Dual Nature of matter, Atom-molecular nuclei, Semi-conductors &
Communication)
1. An electron and a proton are injected into a
uniform electric field at right angle to the field
with the same kinetic energy. What is the nature
of their trajectories?
(a) Electron trajectory is more curved than the
proton trajectory
(b)  Electron trajectory is less curved than the
proton trajectory
(c) Both trajectories are equally curved
(d) Both trajectories are straight lines.
2. When a beam of accelerated electrons hits a target,
continuous X- ray spectrum is emitted from the
target. Which one of the following wavelength is
absent  in the X-rays tube is operated at 40,000 V?
(a) 1.5Å (b)  0.5 Å
(c) 0.25 Å (d) 1.0 Å
3. Ultraviolet radiation of 6.2 eV falls on an
aluminium surface (work function 4.2 eV). The
kinetic energy in joule of the fastest electron
emitted is approximately
(a) 3 × 10
-
21
(b)  3 × 10
-
19

(c) 3 × 10
-
17
(d) 3 × 10
-
15

4. T is the half life period and T
a
is the average life
of a radioactive substance. Which of the following
statement is correct ?
(a) T > T
a

(b)  T is about 69% of T
a
(c) T is inversely proportional to T
a

(d) T and T
a
both are directly proportional to
5. Bi has a half life of 5 days. What time is taken by
(7/8)th part of the sample to decay ?
(a) 3.4 days (b)  10 days
(c) 15 days (d) 20 days.
6. From the following equations pick out the
possible nuclear fusion reaction
(a) 6
C
13
+
1
H
1
?
6
C
14
+ 4.3 MeV
(b)
6
C
12
+
1
H
1
?
7
N
13
+ 2 MeV
(c)
7
N
14
+
1
H
1
?
8
O
16
+ 7.3 MeV
(d)
92
U
235
+
0
n
1
?
54
Xe
140
+
38
Sr
94
+ 2(
0
n
1
) + ? +
200 MeV
7. The stopping potential as a function of frequency
plotted for two
different photoelectric
surfaces A  and B. The
graphs shows that the
work function of A is
(a) greater than that
of B
(b) smaller than that of B
(c) same as that of B
(d) such that no comparison can be done from
given graphs
8. The minimum wavelength of X-rays produced by
accelerating potential V is ?. What will be the
minimum wavelength, when the accelerating
potential is 2 V.
(a) 2 ? (b) 2 ?
(c) ? 2 (d) ?/2
9. The relation between  half life T
1/2
sample and its mean life ? is
(a) T
1/2
= 0.693 t (b) t = 0.693 T
1/2

(c) t = T
1/2
(d) t = 2.718 T
1/2
10. According to Bohr’s theory the radius of electron
in an orbit described by principal quantum
number n and atomic number Z is proportional to
(a) Z
2
n
2
(b) Z
2
/n
2

(c) (Z
2
/n) (d) (n
2
/Z).
11. A transistor is preferable to triode valve because it
(a) can withstand larger changes in temperature
(b) has higher input impedance
(c) can handle larger powers
(d) does not require a heater
12. What is the value of A . A in Boolean algebra :
(a) 0 (b) 1
(c) A (d) A
13. When NPN transistor is used as an amplifier then
(a) electrons move from base to collector
(b) holes move from emitter to base
(c) electrons move from collector to base
(d) holes move from base to emitter
14. In p -type semiconductor :
(a) major current carriers are electrons
(b) major current carriers are mobile negative
ions
(c) major current carriers are mobile holes
(d) the number of mobile holes exceeds the
number of acceptors
15. The diffusion current in a P -N junction is :
(a) from n -side to p -side
(b) from p -side & n -side
(c) from n -side to p -side, if forward biased
(d) from p -side to n -side, if reverse biased
16. n -type germanium is obtained on doping intrinsic
germanium with :
[2]

(a) Phosphorus  (b) Aluminium
(c) Boron  (d) Gold
17. The band gap in germanium and silicon in eV
respectively is :
(a) 0.7, 1.1 (b) 1.1, 0.7
(c) 1.0,0 (d) 0, 1.1
18. An electron and a proton are injected into a
uniform magnetic field perpendicular to it with
the same momentum. What is the nature of their
trajectories ?
(a) Radius of curvature is less for electron
(b)  Radius of curvature is more for electron
(c) Radius of curvature is same for both
(d) Both move along straight lines.
19. The p–n junction diode works as insulator, if
connected
(a) to A.C.  (b) in forward bias
(c) in reverse bias  (d) none of these
20. the reverse process of pair production is called
(a) annihilation of matter
(b) a–decay
(d) carbon–nitrogen cycle
21. The least doped region in a transistor is
(a) emitter
(b) collector
(c) base
(d) either emitter or collector
22. Radiowave frequency 30 MHz to 300 MHz belong
to which of the following ?
(a) HF (b)  UHF
(c) VHF (d) SHF.
23. In which of the following cases the band width as
well as modutation increases ?
(a) DSB (b)  SSB
(c) AM (d) FM.
24. What is the range of frequency of microwaves :
(a) 3 × 10
12
to 3 × 10
9
Hz
(b) 3 × 10
11
to 1 × 10
9
Hz
(c) 3 × 10
10
to 3 × 10
9
Hz
(d) 3 × 10
9
to 1 × 10
9
Hz
25. Which of the following is not the mode of
transmission of radiowaves from one place to
another
(a) Ground wave  (b) Space wave
(c) Sky wave  (d) Carrier wave
In every question a statement of ASSERTION is
followed by a statement of REASON. Mark the
correct answer out of the following choices:
(a) If both ASSERTION and REASON are true
and reason is the correct explanation of the
assertion.
(b) If both ASSERTION and REASON are true
but reason is not the correct explanation of the
assertion.
(c) If ASSERTION is true but REASON is false.
(d) If ASSERTION is false but REASON is true.
26. Assertion: If electrons were not orbiting the
nucleus and were stationary, they would collapse
into the nucleus.
Reason: There is electrostatic attraction between
protons in the nucleus and the orbiting electrons.
27. Assertion: A spectral line is emitted when an
electron rotates in a fixed elliptical orbit.
Reason: The concept of elliptical orbits was put
forth by Sommerfeld.
28. Assertion : Thermionic emission from the surface
of a metal when it is heated to incandescence was
discovered by Thomas Edison.
Reason     : Thermions have negative charge.
29. Assertion : A diode can be used as a rectifier.
Reason     : Electrons are emitted by the cathode
and collected by the anode.
30. Assertion : In a semiconductor, the conduction
electrons have a higher mobility than holes.
Reason     : The electrons experience fewer
collisions.
Test-10 (Dual Nature of matter, Atom-molecular nuclei, Semi-conductors &
Communication)

1 C 6 B 11
D
16
A
21
C
26
B
2 C 7 B 12 A 17 A 22 C 27 D
3 B 8 D 13 A 18 C 23 D 28 B
4 B 9 A 14
C
19
C
24
B
29
A
5 C 10 D 15
B
20 A 25 D 30 C

[3]

SOLUTIONS

1. The path will be parabola given by : y =
2 2
2
x
) KE (
eE
4
1
x
mv
eE
2
1
= ; Since KE is same for both
particles, hence both trajectories are equally
curves.
2. Minimum wavelength = hc/eV.
3. E
k
= 6.2 - 4.2 = 2eV  = 2 × 1.6 × 10
-
19
J = 3.2 × 10
-
19

J
4. T = . T / 1 and
693 . 0
a
= ?
?
; Hence T = 0.693 T
a
.
5. A = A
0

n
2
1
?
?
?
?
?
?
, Here A = (1 - )
8
7
A
0
=
8
1
A
0
. Hence
8
1
A
0
= (A
0
)
n
2
1
?
?
?
?
?
?
. This gives n = 3, Hence t = 3 ×
5 = 15 days.
6. (b)
7. The intersect of the graph with v -axis gives
threshold frequency ? = hv
0
.
8. ?
min
= hc/eV.
9. It is factual relation.
10. r = ) Z / n (
me
h
2
4
2
0
p
e

11. Hence, efficiency is higher.
12. A. A = 0 both when A = 0 or 1.
13. Majority carriers in NPN transistor are electrons.
14. (c)
15. Positive charge carriers that is the holes diffuse
from a region of high concentration to regions of
lower concentration.
16. N -Type semiconductor is obtained by doping
with pentavalent impurities.
17. The forbidden band for germanium (Ge) and
silicon (Si) are 0.7 and 1.1 eV respectively.
18. (c).
19. (c)
20. (a)
21. (c)
22. (c)
23. (d)
24. (b)
25. (d)
26. (b) Both assertion and reason are true but reason
is not the correct explanation of the assertion.
Both the assertion and reason are true. The
assertion has stationary charges whereas the
reason has moving charges, therefore, the reason
cannot explain the assertion.
However, there is an electrostatic force between
the nucleus (positive charge) and the stationary
electrons (negative charge) of the atom. This
electrostatic force is one of attraction. If the
electrons were not orbiting the nucleus but were
free to move, this attractive force would draw
them towards the nucleus. As the distance would
go on decreasing the force of attraction would go
on increasing and the electron would finally fall
into the nucleus.
(Actually this does not happen as the electrons are
not stationary but move around the nucleus in
definite quantized orbits.)
27. (d) Assertion is false but reason is true.
A spectral line will be emitted by the electron only
when there is a change in its orbit i.e. when an
electron goes from a higher orbit to a lower orbit.
When the electron is in a fixed orbit it does not
Like the model of the solar system, Sommerfield
suggested that the orbits of the electron are not
perfect circles. They are elliptical. This helped in
removing some very fine discrepancies between
the observations and predictions based on perfect
circular orbits.
28. (b) Both assertion and reason are true but
reason is not the correct explanation of the
assertion:
The conduction -electrons/free -electrons are free
to move within the melt. They cannot leave the
surface due to attraction of positive ions. At
ordinary temperatures, the average kinetic energy
of the free electrons is insufficient to over come
the surface barrier when a water is heat the
average kinetic energy of free electrons also
increases, as the temperature rise. When the
electrons attain energy sufficient to overcome the
surface barrier, they escape from the metal. This
thermionic emission phenomenon was discovered
by Thomas Alva Edison. The assertion is correct.
Electrons emitted by heating of metals are called
thermions. Hence, thermions carry a negative
charge. The reason is correct. The reason does not
explain the thermionic emission.
29. (a) Both assertion and reason are true and
reason is the correct explanation of the assertion.
Electrons are emitted by the filament (cathode)
and collected by the plate (anode). The current
flows only in one direction from the plate to the
cathode when the plate is at a positive potential.
The reason is correct. This property of the diode,
of unidirectional current is utilized in rectifying
alternate current into a direct current. As long as
there  is a positive potential  on the plate, the
diode conducts but when the potential on the
plate becomes negative the flow of current stops.
[4]

The direct current produced during the positive
half of the cycle has the same variation as that of
the applied alternating voltage. A single diode can
be used as an Half -wave rectifier. A single diode
can be used as a Half -wave rectifier. A full -wave
rectifier, one which gives direct current in the
complete cycle, is made using two or four diode.
30. (c) Assertion is true but reason is false.
Electrons do not experience fewer collisions. The
mobility of electrons is more because they require
less energy to move, not because they are lighter.
```
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