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Energy Change in A Cathode Ray
1. In a cathode ray tube, an electron with kinetic energy of 1.32 10-14 J is accelerated.Calculate the potential difference, Vbetween the cathode and the accelerating anode.
[e = 1.6 x 10 -19 C]Solution:
V1025.8
106.1101.32
2
1energyKinetic
3
1914-
2
=
=
==
V
V
eVmv
2. In a vacuum tube, a cathode ray is produced and accelerated through a potential
difference of 2.5kV. Calculate(a) The initial electric potential energy of the cathode ray.
(b) The maximum velocity of the electron.
[e = 1.6 x 10 -19 C; m= 9 x 10 -31 kg]Solution:
(a) J104105.2106.1energypotentialElectric16319 === eV
(b)142 104
2
1 == eVmv 2109
10431
142
=
v -1816 ms1098.21089.8 ==v
3. If the potential difference between the cathode and the anode in a CRO is 3.5 kV,
calculate the maximum speed of the electron which hit the screen of CRO.[e = 1.6 x 10 -19 C; m= 9 x 10 -31 kg]Solution:
163192106.5105.3106.1
2
1 === eVmv
15
31
162 1024.12
109
106.5=
=
v -1615 ms1053.31024.1 ==v
2
By using the principle of conservation of energy,,
Maximum velocity of electron,
v = velocity of electron
V = Potential difference between Anode and
Cathode
e = Charge on 1 electron = 1.6 x 10 -19 C
Figure 9.2
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9.1.4 : The working Principle of the Cathode-Ray Oscilloscope.
1. Fill in the blank the structure of CRO.
9.1.5 Uses of the CRO.
1. The uses of cathode-ray oscilloscope are:
(a) ..
(b) .
(c) .
2. If the CRO in figure uses Y-gains of 1.5 Vcm-1, calculate the value ofVpp.Solution:
0.30.25.1 ==V V
4
To measure a D.C voltage:The unknown voltage, V= (Y-gain) h
To measure a A.C voltage:
Peak-to-peak voltage, Vpp = (Y-gains) h
Peak voltage, Vp= (Y-gains)2
1 (h)
Effective voltage or root-mean-square voltage, Vr.m.s= pV2
1
Short time intervals, t= no. of divisions between two pulses time-base value.
Figure 9.4
Figure 9.5
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3. The figure shows a trace on a CRO set at 5 Volt per division on the vertical axis.
(a) What is the maximum voltage (peak voltage)indicated?
Solution:
Peak voltage, Vp= (Y-gains)2
1 (h)
divsV/divVP 42
15 =
VVP 10=
4. Figure shows a trace on an oscilloscope for an a.c source.If the Y-gain is set to 1.5 Vcm-1 and the time-base is 2 ms
cm-1.
(a) Calculate the peak voltage,Vp of the a.c source.Solution:
cmVcmV1-
P 42
15.1 =
VVP 0.3=
(b) Calculate the frequency,fof the a.c source.
Solution:24 = cmT ms cm-1
T = 8 ms f = 1251=
THz
(c) Sketch the trace displayed on the screen if the settings are changed to 1 Vcm-1 and 1
ms cm-1.
5. The diagram shows the trace on the screen of a CRO when an
a.c voltage is connected to the Y-input. The Y-gain control isset at 2 V/div and the time base is off.
Calculate the value of :
(a) Peak-to-peak voltage, Vpp(b)Peak voltage, Vp.
(c)Root-mean-square voltage, Vr.m.s
Solution:
5
Figure 9.6
Figure 9.7
Figure 9.8
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5 divs
JPN Pahang Physics Module Form 5Students Copy Chapter 9: Electronics
(a) Peak-to-peak voltage, Vpp = (Y-gains) h
= 2V/div 6 divs= 12 V
(b) Peak voltage, Vp = 6 V
(c) Vr.m.s = pV
2
1= 24.46
2
1= V
6. When two claps are made close to a microphone which is connected tothe Y-input and earth terminals, both pulses will be
displayed on the screen at a short interval apart as shown in
figure below. Measure the time lapse between the twoclaps.
Solution:
7. Figure shows the trace displayed on the screen of a
CRO with the time-base is set to 10 ms/div. What is thefrequency,fof the wave?
Solution:
8. An ultrasound signal is transmitted vertically down to the sea bed. Transmitted and
reflected signals are input into an oscilloscope with a time base setting of 150 ms cm-1.
The diagram shows the trace of the two signals on the screen of the oscilloscope. Thespeed of sound in water is 1200 ms-1. What is the depth of the sea?
Solution:
9.2 SEMICONDUCTOR DIODES
6
s/div
Length between two pulses = 5 divs
Time taken, t = 5 divs 10 ms/div= 50 ms
Time interval = 0.05 s
m1502
0.251200dHance,
t
2dVwaves,ultrasonicofSpeed
s0.25ms250smms50cm5QandPbetweentimed2
ofdistanceathroughtraveltowavesultrasonicfortakenTime
1-
=
=
=
===
=
Distance for two complete wave = 2 divs
Time taken = 2 divs 10ms/div
= 20 ms
frequency, f =T1 =
ms201 = 50 Hz
Figure 9.9
Figure 9.10
Figure 9.11
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9.2.1 Properties of Semiconductors
1. Semiconductor is
..
.
2. Give the examples of pure semiconductor:
(a)
(b) ...
(c)
9. What is the doping process?
10. Base on the figure, complete the statement below.
(a) n-type semiconductors
Silicon like Silicon doped with atoms such as or
phosphorus . the number offree electron. The phosphorus atoms have
.. valence electrons, with being used in the formation of covalent bonds. The
fifth electron is free to move through the silicon. The silicon has .
.. as majority charge-carriers and it thus known as an n-type semiconductor.
7
a group of materials that can conduct better than insulators but not as
good as metal conductors.
Silicon
Germanium
Selenium
Doping is a process of adding a certain amount of other substances calleddopantssuch
asAntimony andBoron to a semiconductor, to increase its conductivity.
pentavalent antimony
increases
negativeelectrons
five four
Figure 9.12
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(b) p-type semiconductors
Semiconductor like Silicon doped with .. atoms such as
or indium has more positive holes. The Boron atoms have only .
valence electrons; hence .of the covalent bonds has a missing electron.This missing electron is called a positive hole. The majority charge-carriers in
this semiconductor are the . and this semiconductor is thus known
as a p-type semiconductor.
9.2.2 The p-n junction (Semiconductor diode)
1. What is the function of semiconductor diode?
2. Label the p-n junction below and draw a symbol of the diode.
8
trivalent Boron
positiveholes
three
one
The function of semiconductor diode is to allow current to flow through it in one direction
only.
Figure 9.13
p-type n-type
Positive hole Negative electron Symbol
p-n junctionFigure 9.13
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3. ( a) Forward-biased
(i) In forward-bias, the p-type of the diode is connected to . and the n-
type is connected to the of the battery.
(ii) Complete the diagram below to show the diode is in forward-bias.
(iii) Draw arrows to show the current, electrons and holes flow in the diagram.
(b) Reverse-biased
(i) In reverse-bias, the p-type of the diode is connected to . , and the n-
type is connected to the of the battery.
(ii) Complete the diagram below to show the diode is in reverse-bias.
4. Draw arrows to show the current, electrons and holes flow in the diagram.
5. What the meaning of rectification?
9
negative terminal
positive terminal
positive terminal
negative terminal
The bulb is light up
The bulb does not light up
The bulb is light up
The bulb does not light up
Rectification is a process to convert an alternating current into a direct current by using a diode.
Figure 9.14
Figure 9.15
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6. The figure shows a half-wave rectifier circuit that is connected to CRO.
(i) Sketch waveform of the voltages observed on the CRO screen when the time-
base is on.
(ii) Sketch waveform of the voltages observed on the CRO screen when a
capacitor is connected in parallel across a resistor, R.
7. The figure shows a full-wave rectifier circuit that is connected to CRO.
(i) Draw arrows to show the current flow in thefirst half cycle and
to show the current flow insecond half cycle in the diagram.(ii) Sketch the waveform of the voltages observed on the CRO screen when the
time-base is on.
10
To CRO
Figure 9.16
Figure 9.17
Figure 9.18
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(iii) Sketch waveform of the voltages observed on the CRO screen when a
capacitor is connected in parallel across a resistor, R.
8. What is the function of the capacitor?
....
9.3 TRANSISTOR
9. 3.1 Terminals of a Transistor.
1. What is a transistor?
2. Draw and label symbol of n-p-n transistor and p-n-p transistor.
3. State the function for each terminal in a transistor.
(a) The emitter, E :
.
(b) The base, B :
(c) The collector, C:
...
11
Acts as a current regulator or smoother.
To CRO
a
A transistor is a silicon chip which has three terminals labeled as base, collector and emitter.
n-p-n transistor
Base, B
Collector, C
Emitter, E
p-n-p transistor
Base, B
Collector, C
Emitter, E
Acts as a source of charge carriers, providing electrons to the collector.
Controls the movement of charge carriers (electrons) from the emitter (E) to the collector (C)
Receives the charge carriers from the emitter (E)
Figure 9.19
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9.3.2 Transistor circuit
1. (a) Transistor circuit with 2 batteries.
(b) Transistor circuit with 1 battery.
2. The working circuit of a transistor used as a potential divider can be connected as shown
in figure. The voltage across Rx and Ry can be calculated as follows.
V
RR
RVx
yx
x
+
= VRR
RV
yx
y
Y
+
=
12
BE : .CE : .
Ib : .
Ic : .
R1 : ...
R2 : ...
E1 : ...
E2 : ...
Rx : ...
Base circuit
Collector circuit
Base current
Collector current
Limit the base current
Limit the collector current
Supply energy to the base circuit
Supply energy to circuit.
Potential divider
Potential divider
Ie
Remember:
Ie = Ib + Ic
Ie > Ic > Ib
Ic >>>>IbNo Ib No Ic
Ie
Figure 9.20
Figure 9.21
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(a) Figure shows a transistor circuit. The bulb can be lighted up when potential difference, V
across resistor P is 2V and resistance P is 10 k. Calculate the maximum resistance, S sothat the bulb is lighted up.
9.2.3 Transistor as an Automatic Switch.
1. Complete the statement below.
The switching action is produced by using a potential divider. In a working circuit
shown in figure, a resistor, RX and a . are being used to form a
potential divider. If the variable resistor is set to zero, the base voltage is . and
the transistor switches . However, if the resistance of the variable resistor is
increased, the base voltage will. When the base voltage reached a certain
minimum value, the base current,IB switches on the transistor. A large collector current,
ICflows to light up the bulb.
2. What type of transistor is used in an automatic switch circuit?
13
Bulb
Solution:
V
RR
RV
ps
p
p
+=
( )V6
1010
1010V2
3
3
+
=
sR
3000010103 =+SR
== kRS 2020000
IC
IE
IB
RX
RYBase voltage
Battery voltage
increases
variable resistor
zero
off
Transistor n-p-n
Figure 9.22
Figure 9.23
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3. (a) Light Controlled Switch
(i) Complete the statement below.
Figure shows a transistor-based circuit that functions as a light controlled switch.
The .. (LDR) has a very high resistance in the . and a low
resistor in ... R is a fixed . The LDR and R form a potential
divider in the circuit.
In bright light, the LDR has a very . resistance compared to R. Therefore, the base
voltage of the transistor is too .. to switch on the transistor.
In darkness, the resistance of the LDR is very and the voltage across the LDR is
enough to switch on the transistor and thus lights up the bulb. This circuit can beused to automatically switch the bulb at night.
(ii) Complete the table below.
Condition R LDR VLDR R VR Transistor (ON or OFF)
Daylight
Darkness
RememberIc >>>>Ib
(iii) How can the circuit in figure be modified to switch on the light at daytime?
..
(b) A Heat-Controlled Switch
14
light-dependent resistor dark
bright light resistor
low
low
large
high
on
low lowhigh high
highhigh
low low ON
OFF
The circuit can be modified by interchanging the positions of the LDR and resistor R.
IC
IE
1k
R
LDR
10 k
6 V
Figure 9.24
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(i) Complete the statement below.
Figure shows a transistor-based circuit that function as a heat controlled switch.
A ..is a special type of resistor. Its resistance becomes very when it is
cold. When the thermistor is heated, its resistance rapidly. At room
temperature, the thermistor has a . resistance compared to R. Therefore, the base
voltage of the transistor is too low to switch on the transistor.
When the thermistor is heated, its . drops considerablely compared to R.
Therefore, the ., VB is high enough to switch . the transistor. When the
transistor is switch on, the relay switch is activated and the relay is switched . The
circuit can also be used in a fire alarm system.
(ii) What is the function of a diode is used in the heat-controlled circuit?
..
..
(iii) Complete the table below.
Temperature RThermistor VThermistor R VR Transistor (ON or OFF)
High
Low
RememberIc >>>>Ib
9.2.4 Transistor as a Current Amplfier
1. Complete the statement below.
15
thermistor high
dropshigh
resistance
basevoltage on
To protect the transistor from being damaged by the large induced e.m.f in the relay coil
when the collector current, ICdrops to zero.
IC
IE
R1
R2
RI
B
mA
A
low lowhigh high
highhigh
low low
ON
OFF
on
Relay
Alarm
RB
R
Thermistor Diode
Figure 9.25
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A transistor functions as a current amplifier by allowing a small current to control a larger
current. The magnitude of the ., IC is primarily determined by the
.., IB. A .. change in the base current, IB will cause a .. change in
the collector current, IC. The current amplification can be calculated as follows:
2. Name the type of the transistor used.
3. What will happened to the readings of the miliammeter, mA and microammeter,A when
the resistance of R is reduced?
4. A transistor is said to have two states, the ON state and OFF state.
(a) Explain the meaning of the ON state of a transistor.
(b) Explain the meaning of the OFF state of a transistor.
(c) What is the function of the rheostat, R?
(d) What is the function of the resistor, S?
9.4 Logic Gates
9.4.1 Analysing Logic gates
16
Current AmplificationB
C
I
I
=
collectorcurrent
basecurrent small big
When a transistor is in the ON state, currents flow in the base and in the collector circuit.
When a transistor is in the ON state, there is no current in the base and in the collector
circuit.
To change the base current.
To control and limit the base current.
n-p-n transistor
The readings on miliammeter and microammeter increase.
Figure 9.26
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1. What is a logic gate?
2. Complete the table below.
Gates Symbol Truth table
AND gate
OR gate
NOT gate
17
A switching circuit that is applied in computer in computer and other electronic devices.
B
B
Input Output
A B Y
0 0 0
0 1 0
1 0 0
1 1 1
Input Output
A B Y
0 0 0
0 1 1
1 0 1
1 1 1
Input Output
A Y
0 1
1 0
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NAND
gate
NOR gate
9.4.2 Combinations of logic Gates
1. Find the output Y for each combination of logic gates.
The truth table:
2. 000
Input Output
A B P Y
0 0 1 0
0 1 1 11 0 0 0
1 1 0 0
18
B
B
Y
B
P0 0 1 1
0 1 0 1
0 1 0 0
1 1 0 0
P0 0 1 1
Figure 9.27
Input Output
A B Y
0 0 1
0 1 1
1 0 11 1 0
Input Output
A B Y
0 0 1
0 1 0
1 0 0
1 1 0
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The truth table:
3.
The truth table:
Input Output
A B P Q Y
0 0 1 1 1
0 1 1 0 0
1 0 0 1 01 1 0 0 0
19
Y
A
B
0 1 0 1
1 0 0 0
1 1 0 0
1 0 1 0Q
YB
B
0011
0101
0 0 0 1
1 0 1 0
0 1 0 0
Figure 9.28
Figure 9.29
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4.
The truth table:
Input Output
A B B X Y
0 0 1 0 0
0 1 0 0 11 0 1 0 0
1 1 0 1 0
Input Output
A B P Q Y
0 0 1 0 0
0 1 1 1 1
1 0 1 1 11 1 0 1 0
20
Y
B
P
Q
0011
0101
1110
0111
0110
Figure 9.30
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5.
The truth table:
6. Figure shows a logic gate system which switches on an air-conditioner automatically.
Keys:
The light detector (Input J): In the day, logic 1.
Input Output
P Q R Q S
1 0 1 1 1
0 1 1 0 0
1 1 0 0 0
0 0 1 1 1
21
Q
S
RP
Q
Figure 9.31
L
Lightdetector
Heatdetector
Input J
Input K
Air-conditioner
Figure 9.32
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At night, logic 0.
The heat detector (Input K): Hot, logic 1.
Cool logic 0.
(a) Complete the truth table below:
(b) Based on the truth table in (a), state the conditions in which the air-conditioner conditions
in which the air-conditioner will operate and function normally.
Reinforcement Chapter 9
Part A: Objective questions
1. Which of the following is not a propertyof cathode rays?
A. It is positively charged.
B. It travels in a straight line.
C. It can be deflected by magnetic field.D. It can be deflected by electric field.
Input Output
J K L
0 0
0 1
1 0
1 1
22
- On a hot say or daytime On a hot night
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2. Cathode rays consists of
A. Fluorescent particlesB. Light rays from a screen
C. Beams of fast moving particles
D. Light rays from hot filament
3. A beam of electrons is being deflected
due to a potential difference betweenplates P and Q.
Which of the following statements is nottrue?
A. The potential at plate P is positive.B. The deflection would be greater ifthe potential difference is greater.
C. The deflection would be greater if
the electrons are moving faster.D. The electron beam will return to
straight line if a suitable magnetic
field is applied between the plates.
4. The figure 9.34 shows the trace
displayed on a CRO with the Y-gain
control is turned to 3.75 V/div.What is the maximum value of the
potential difference being measured?
A. 2.5 V
B. 5.5 V
C. 7.5 VD. 12.5 V
E. 15.0 V
5. In p-type semiconductor
A. The number of holes are equal to the
number of electrons.
B. The number of the holes are more
than the number of electrons.C. The number of the holes are less than
the number of electrons.
6. Which of the following is not true aboutdiode?
A. It can be used to rectify alternatingcurrent.
B. It can only conduct electricity when
it is connected in forward in forward
bias in a circuit.C. It is formed by joining an n-type and
a p-type semiconductor.
D. The majority charge carriers in thediode are electrons.
7. The figure 9. 35 shows the arrangementof silicon atoms after an atom P is doped
to form an extrinsic semiconductor.
Which of the following is not true?
A. The conductivity of thesemiconductor increases.
B. The semiconductor becomes an n-
type.C. The majority charge carrier is
electron.
D. Atom P is a trivalent atom.
8. The figure 9.36 shows a rectifier circuit.
Which of the following statements is
true?
23
Figure 9.36
Figure 9.34
Figure 9.35
Q
Figure 9.33
P
Q
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A. A rectifier changes d.c to a.c.
B. Device P allows current to flow inany directions.
C. Device Q acts as a rectifier.
D. The rectifier circuit would still work
if device P is reversed.
9. The figure 9.37 shows a circuitconsisting of two diodes and a bulb.
When the switch is on, the bulb does not
light up.
What needs to be done to light up thebulb?
A. Replace the diode with a new one.B. Reverse the connection of the diode.
C. Increase the number of bulbs.
D. Connect a resistor in series with the
bulb.
10.
Figure 9.38 shows four identical bulbs,
P, Q, R and S, and four electroniccomponents connected in a circuit.
Which of the following bulbs will light
up continuously when the switch is on?A. P and Q only
B. P, Q and R only
C. R and S onlyD. P, Q and S only
11. Which of the following circuits showsthe connect directions of the base current
IB, emitter current, IE and collector
current, IC?
12. Which of the following statements abouta transistor is not true?
A. A transistor can act as an amplifierB. A transistor can act as a relay switch.C. The function of a transistor is the
same as that of two diodes.
D. A transistor is a combination of twotypes of semiconductors.
24
Figure 9.37
Figure 9.38
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13. What is the function of the transistorcircuit shown in figure 9.39?
A. As an amplifier
B. As a rectifierC. As a switch device
D. As a modulator
14. The figure 9.40 shows a transistor being
used as a current amplifier.
Which of the following is correct?A. IB > ICB. IB = ICC. IB < IC
15. Figure 9.41 shows a circuit consisting of
a transistor which acts as an automatic
switch. When the potential differenceacross the thermistor is 3 V and the
resistance of the thermistor is 1000 ,the resistance value of resistor, R is ..
A. 3 k B. 4 k
C. 5 k D. 6 k E. 7 k
16. The figure 9. 42 shows a transistor
circuit being used to amplify sound.
Which of the following is not correctabout the circuit?A. T is an npn transistor
B. The capasitor prevents d.c current
but allows a.c current to pass throughit.
C. Speaker amplifies the sound.
D. R1 and R2 act as potential divider.
17. The figure 9.43 shows a logic gate
circuit with input signals, X and Y.
Which of the following is the output
signal?
18. The figure 9.44 shows a logic gatecircuit.
25
Figure 9.41
Figure 9.42
M- MicrophonC- Capacitor
S- Speaker
Figure 9.43
Figure 9.43
IB IC
Figure 9.40
Figure 9.39
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Which of the following is the output
signal Z?A. 0110
B. 1010
C. 1110
D. 0101
19. The figure 9.44 shows the combinationof three logic gates.
The truth table for the combination of
tree logic gates is as follows.
What is gate X?A. AND
B. NOR
C. OR D. NAND
20. The figure 9. 45 shows a combination ofthree logic gates in a logic circuit. When
inputs P and Q are both 1 output Y is 1.
Which of the following logic gates can
be used to represent J and K?
A.B.
C.
D.
J K
AND NOR NAND NOR
OR AND
NOR AND
Part B: Structured Questions.
1. Figure 9.46 shows a trace obtained on an oscilloscope screen when an a.c voltage is
connected to the Y-plates of an oscilloscope.
(a) Explain what is meant by thermionic emission.
(b) Determine the peak voltage of a.c voltage.
(c) Determine the time for one complete oscillation on the screen.
(d) What is the frequency of the a.c voltage?
26
Figure 9.45
Figure 9.44
YJ
K
Figure 9.46
Emission of electrons from the surface of a metal by heat.
2 x 3 = 6V
2 x 5 = 10 ms
f =1/T=50 Hz
Scale: 1 division = 1 cm
The Y-gain is set at 3 V/cmThe time base is set at 5 ms/cm
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(e) With the same a.c voltage applied to the oscilloscope, the time-base setting is altered to
2.5 ms/cm and the Y-gain setting is altered to 2 V/cm. On the space below, sketch the new
trace would appear on the oscilloscope.
2. Figure 9. 47 shows a full wave bridge rectifier. The a.c supply has a frequency of 50 Hz.
(a) When the polarity of the a.c supply voltage is positive at A, state the two diodes which
are forward biased.
..
(b) When the polarity of the a.c supply voltage is negative at A, state the two diodes which
are forward biased.
(c) Using the axes in figure 9.48, sketch the voltage-time graph across the resistor, R.
(d) On the figure 9.49, sketch the voltage-time graph across the resistor if a capacitor is
connected across the resistor if a capacitor is connected across the resistor R parallel withthe resistor.
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D2 and D4
D1 and D3
Figure 9.47
Figure 9.48 Time/ms
Voltage/V
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(e) Explain how the capacitor causes the voltage across the resistor to vary with time in the
way that you have drawn.
3. A student wants to build a simple lift motor control system which operates using two buttons,
A and B for a two-storey building.
A: Up buttonB: Down buttonThe lift motor only activates when someone presses any one of the buttons. Figure 9.50
shows the circuit that can be used to activate the motor.
Keys:
Buttons A and B : When pressed, logic 1Not pressed, logic 0
X Output : Motor is activated, logic 1
(a) The truth table below shows the operations of the logic gates in a lift motor control
system.
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The charging of the capacitor by the power supply and the discharging of the capacitor
through the resistor will smooth the output.
Figure 9.49Time/ms
Voltage/V
12 V
0 V
A
B
Logic gate
X 240 V
Relay switch Moto
Figure 9.50
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(i) Us
ing
the
keys given, complete the truth table.
(ii) Name the logic gate in the circuit in the figure 9.50.
(iii) In the space below, draw the logic gate symbol in 3(a)(ii).
(b) Why is a relay switch needed in the circuit?
(c) The door of the lift is fitted with a light transmitter and a detector which is a light
dependent resistor, LDR. If the light dependent resistor detects light, the relay switch is
activated and the lift door will close. Figure 9.51 shows an electronic circuit for the
control system of the lift door.
(i) State the relationship between the resistance and the intensity of light received
by the light dependent resistor, LDR.
Input Output
A B X
0 0 0
0 1 11 0 1
1 1 0
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RMotor
240 V
Figure 9.51
AND Gate
The higher the light intensity, the lower the resistance of the resistor.
Activates large current in the main secondary circuit supply// small current at
the output cannot activate the motor.
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(ii) Complete the circuit in figure 9.51 by drawing the resistor and the light
dependent resistor using the symbols given below.
(iii) Explain how the circuit functions.
Part C: Essay Questions
1.
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Light dependent resistorResistor
High light intensity produces lower resistance and high base voltage
- A bigger base current flows and activates the transistor
- A big collector current flows through the relay switch and activates the
circuit of the door motor.
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(a) The diode, bulb and battery in circuit X and circuit Y of figures 9.52 and 9.53 are
identical.
(i) What is meant by a direct currentand an alternating current? [2 marks]
(ii) Using Figures 9.52 and figure 9.53, compare the connection of the diodes and the
conditions of the bulbs. Relating the connection of the diodes and the conditions
of the bulbs, deduce the function of a diode. [5 marks]
(iii) State the use of a diode. [1 mark]
(b) A semiconductor diode is made by joining a p-type semiconductor with a n-typesemiconductor. Describe and explain the production and the characteristics of a p-typesemiconductor and a n-type semiconductor. [4 marks]
2. Figure 9.55 shows four circuits W, X, Y and Z, each has an ideal transformer and the circuit
are used for the purpose of rectification.
(i) What is meant by rectification? [1mark]
(ii) Explain the working principle of a transformer. [3 marks]
31
Figure 9.52 Figure 9.53
Circuit ZCircuit X
Circuit WCircuit Y
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1
2 3
4
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JPN Pahang Physics Module Form 5Students Copy Chapter 9: Electronics
(iii) You are asked to make a 12 V battery charger. Study the circuits W, X, Y and Z in
figures 9.55 and consider the following aspects:
Type of transformer The number of turns in the primary coil and in the secondary coil. Type of rectification
Characteristics of output currentExplain the suitability of the above aspects and hence, determine the most suitablecircuit to make the battery charge. [6 marks]
3. A student carries out an experiment to determine the relationship between the collectorcurrent IC to the base current IB of a transistor.
Transistor T is connected to fixed resistor R1 =1k and R2 = 56 k and a rheostat R3 asshown in figure 9.56. The battery supplies a voltage of 6 V to the transistor circuit.
Rheostat R3 is adjusted until the current IB detected by microammeter A1 is 10 A. Thecollector current, IC recorded by miliammeter A2 is shown in figure 9.57(a).
Rheostat R3 is then adjusted to lower value so that microammeter A1 gives IB = 20 A, 30
A, 40 A, 50 A and 60 A. The corresponding readings of IC on miliammeter, A2 are shown
in figure 9.57(b), 9.57(c), 9.57(d), 9.57(e) and 9.57(f).
32
(a) IB = 10A
mA
31
T6V
R1
= 1k
A2
IC
A1
IB
R2
= 56kR2 = 2k
Figure 9.56
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(a) For the experiment described identify
(i) the manipulated variable : ..
(ii) the responding variable : ..
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0
1
2 3
4
50
1
2 3
4
5
0
1
2 3
4
50
1
2 3
4
5
mA mA
0
1
2 3
4
5
(e) IB = 60A
(c) IB = 40A
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(b) IB = 30A
mA
(d) IB = 50A
(b) IB = 20A
mAmA
The supply voltage
The collector current, IC
The base current, IB
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(iii) the fixed variable : ..
(b) From the figure in 9.57, record the collector current, IC when IB = 10, 20, 30, 40, 50 and 60
A. Tabulate your results for IB and IC in the space given below.
IB/
A IC/mA
10 0.8
20 1.6
30 2.4
40 3.1
50 3.9
60 4.8
(c) On a graph paper, draw a graph of IC against IB.
(d) Based on your graph, determine the relationship between IC and IB.
4. Figure 9.58 shows a microphone connected to a power amplifier. When the microphone has
detected a sound, an amplified sound is given out through the loudspeaker. The soundbecomes louder if the volume of the amplifier is turned on to increase the power.
Using the information based on the observation of the brightness of the bulbs,(a) Make one suitable inference.
(b) State one appropriate hypothesis that could be investigated.
(c) Design an experiment to investigate the hypothesis stated in (b). Choose suitableapparatus such as a diode, rheostat and others.
In your description, state clearly the following:
34
Ic is directly proportional to IB
Figure 9.58
LoudspeakerPower amplifier
Volume control
Microphone
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(i) Aim of the experiment,
(ii) Variables in the experiment,(iii) List of apparatus and materials,
(iv) Arrangement of the apparatus,
(v) The procedure of the experiment, which includes the method of controlling
the manipulated variable and the method of measuring the respondingvariable,
(vi) The way you would tabulate the data,(vii) That way you would analyse the data.