The document discusses transistors and their uses. It explains that transistors are made of semiconductor materials and are used as electronic switches or amplifiers. There are two main types of transistors - NPN and PNP. The document also describes how transistors are used in automatic switches that are controlled by light or heat. Light controlled switches use light-dependent resistors while heat controlled switches use thermistors.

1. Author : Khairi
TRANSISTOR
 Transistor is made of
semiconductor material
 Transistor is produced by
attaching n-type semiconductor
and p-type semiconductor
 Transistor is used as electronic
switching or current amplifier
 There two types of transistor ;
npn transistor and
pnp transistor

2. Author : Khairi
TRANSISTOR
n p n attachment
n p n
p n p attachment
p n p
npn transistor
pnp transistor
PRODUCING A TRANSISTOR

3. Author : Khairi
TERMINALS OF TRANSISTOR
n p n
npn transistor
collector,C
base,B
emitter,E
SYMBOL
C
B
E
TRANSISTOR

4. Author : Khairi
p n p
pnp transistor
collector,C
base,B
emitter,E
SYMBOL
C
B
E
TRANSISTOR
TERMINALS OF TRANSISTOR

5. Author : Khairi
AMPLIFIER
Amplifier is used to amplified current
Amplifier is widely used as audio amplifier such as in
radio and television
Transistor is used to build an amplifier
TRANSISTOR

6. Author : Khairi
Connection of npn transistor as an amplifier
RB
Base circuit
BE junction
Forward biased
B
E
Collector circuit
BC junction
Reverse biased
C
TRANSISTOR
C ----- +
B ----- +
- --- E --- -

7. Author : Khairi
RB
B
E
C
When base current ,IB flows
IB
Collector current, IC flows through transistor
IC
Emitter current,IE is produced
IE
IE = IB + IC
A bigger magnitude of current produced
TRANSISTOR
Connection of npn transistor as an amplifier

8. Author : Khairi
There are 2 types of automatic controlled switch :
1. Light controlled automatic switch
e.g. Street lights will be switched on at night
and will be switched off at daytime automatically
2. Heat controlled automatic switch
e.g. Fire alarm will sound automatically when the fire occurs
AUTOMATIC SWITCH

9. Author : Khairi
BASIC UNDERSTANDING OF AUTOMATIC SWITCH
Vi
R1
R2
VB
VB = Vi
R1 + R2
R2
Value of VB (potential difference across R2) is very important in
determining whether the transistor
is activated(turn on) or not activated(turn off)
Value of VB is depending on R2 and R1
AUTOMATIC SWITCH

10. Author : Khairi
VB = Vi
R1 + R2
R2
If R2 is high - VB becomes high - transistor is activated
AUTOMATIC SWITCH
BASIC UNDERSTANDING OF AUTOMATIC SWITCH
Vi
R1
R2
VB

11. Author : Khairi
VB = Vi
R1 + R2
R2
If R2 is high - VB becomes high - transistor is activated
AUTOMATIC SWITCH
BASIC UNDERSTANDING OF AUTOMATIC SWITCH
Vi
R1
R2
VB

12. Author : Khairi
VB = Vi
R1 + R2
R2
If R2 is low - VB becomes low – transistor is not activated
AUTOMATIC SWITCH
BASIC UNDERSTANDING OF AUTOMATIC SWITCH
Vi
R1
R2
VB

13. Author : Khairi
LIGHT CONTROLLED AUTOMATIC SWITCH
LDR
Light controlled automatic switch uses light dependent resistor (LDR)
Resistance of LDR is high in the darkness
and low in bright light
Dark --- R high
Light ---- R low
AUTOMATIC SWITCH

14. Author : Khairi
LDR
Light bulb
RB
R1
R2
AUTOMATIC SWITCH
LIGHT CONTROLLED AUTOMATIC SWITCH

15. Author : Khairi
LDR
Light
bulb
RB
R1
R2
In bright light
 Resistance of LDR is low
 Potential difference of VB is low
VB
 Based current,IB is small
IB
 Transistor is not activated
 IC does not flow
 Light bulb does not light up
VB = Vi
R1 + R2
R2
AUTOMATIC SWITCH
LIGHT CONTROLLED AUTOMATIC SWITCH

16. Author : Khairi
LDR
Light
bulb
RB
R1
R2
In the darkness
 Resistance of LDR is high
 Potential difference of VB is high
VB
 Base current,IB is big
IB
 Transistor is activated
 IC flows through transistor
IC
 Light bulb lights up
VB = Vi
R1 + R2
R2
AUTOMATIC SWITCH
LIGHT CONTROLLED AUTOMATIC SWITCH

17. Author : Khairi
EXERCISE
LDR Light
bulb
RB
R1
R2
Explain what happen in the darkness and bright light situation
VB = Vi
R1 + R2
R2
Bright light, R1 low, VB high,
IC flows through transistor and light bulb lights up
IB big, transistor is activated,
AUTOMATIC SWITCH

18. Author : Khairi
LDR Light
bulb
RB
R1
R2
VB = Vi
R1 + R2
R2
Dark, R1 high, VB low,
IC does not flow through transistor and light bulb does not light up
IB small, transistor is not activated,
AUTOMATIC SWITCH
EXERCISE
Explain what happen in the darkness and bright light situation

19. Author : Khairi
HEAT CONTROLLED AUTOMATIC SWITCH
thermistor
Heat controlled automatic switch uses thermistor
Resistance of thermistor is low when the temperature is high
Resistance of thermistor is high when the temperature is low
AUTOMATIC SWITCH

20. Author : Khairi
thermistor
RB
R1
R2
siren
AUTOMATIC SWITCH
HEAT CONTROLLED AUTOMATIC SWITCH

21. Author : Khairi
thermistor
RB
R1
R2
siren
VB = Vi
R1 + R2
R2
High temperature
 Resistance of thermistor is low
 R1 low
 VB big
VB
 IB big
IB
 Transistor is activated
 IC flows through transistor
IC
 Siren sounds
AUTOMATIC SWITCH
HEAT CONTROLLED AUTOMATIC SWITCH

22. Author : Khairi
thermistor
RB
R1
R2
siren
VB = Vi
R1 + R2
R2
Low temperature
 Resistance of thermistor is high
 R1 high
 VB small
VB
 IB small
IB
 Transistor is not activated
 IC does not flow
 Siren does not sound
AUTOMATIC SWITCH
HEAT CONTROLLED AUTOMATIC SWITCH

23. Author : Khairi
EXERCISE
thermistor
RB
R1
R2
siren
Vi = 6.0 V
10 kΩ
Siren is set to make a sound when the potential difference across R2
is 4.0 V.
Determine the resistance of thermistor that enable the siren to sound
AUTOMATIC SWITCH

24. Author : Khairi
thermistor
RB
R1
R2
siren
Vi = 6.0 V
10 kΩ
VB = Vi
R1 + R2
R2 4 = 6 [10 000/(R1 + 10 000)]
4 = 60 000/(R1 + 10 000)
R1 + 10 000 = 60 000/4
R1 = 5 kΩ
AUTOMATIC SWITCH
Siren is set to make a sound when the potential difference across R2
is 4.0 V.
EXERCISE

25. Author : Khairi
thermistor
RB
R1
R2
siren
Vi = 6.0 V
10 kΩ
Siren is set to make a sound when the potential difference across R2
is 2.0 V.If in a fire,the resistance of thermistor becomes 20 kΩ.
Will the siren sound ?
VB = Vi
R1 + R2
R2
VB = 6 [10 000/(20 000 + 10 000)]
VB = 2 V VB = 2.0 V
Siren sounds
AUTOMATIC SWITCH
EXERCISE

26. Author : Khairi
thermistor
R1
R2
siren
Vi = 6.0 V
Modify the circuit to control a fan which turn on when temperature is high.
Explain how your circuit works.
AUTOMATIC SWITCH
EXERCISE

27. Author : Khairi
thermistor
R2
R1
Vi = 6.0 V
AUTOMATIC SWITCH
EXERCISE
Thermistor is interchange with R1
Siren is replaced with relay
Relay is connected to fan and 240 V ac power supply
fan
240 V
ac

28. Author : Khairi
thermistor
R2
R1
Vi = 6.0 V
AUTOMATIC SWITCH
EXERCISE
 When temperature is high,the resistance of thermistor becomes low.
 Potential difference across R1 becomes high.
 IC flows and relay is turned on.
fan
240 V
ac
 IB flows and transistor is activated.
 Relay switches on the secondary circuit of 240 V ac and fan.

29. Author : Khairi
Which of the following is correct about the transistor ?
Electrode P Type of transistor
A. Emitter pnp
B. collector pnp
C. Emitter npn
D. Collector npn
PAST YEARS QUESTION
PAST YEARS QUESTION

30. Author : Khairi
In which circuit does the bulb light up ?
Rules
C --- +
B --- +
- --- E --- -
PAST YEARS QUESTION
PAST YEARS QUESTION

31. Author : Khairi
What change should be done to light up the bulb during the day time ?
A. Reverse the terminal of battery
B. Interchange R1 and R2
C. Replace the npn transistor with a pnp transistor
D. Replace resistor R3 with a resistor of lower
resistance
PAST YEARS QUESTION
PAST YEARS QUESTION

32. Author : Khairi
Which circuit will the light-emitting diode (LED) light up when the
switch is on ?
A. B. C. D.
Rules
C --- +
B --- +
- --- E --- -
PAST YEARS QUESTION
PAST YEARS QUESTION

33. Author : Khairi
a. State the relationship between resistance and intensity of light
received by the light dependent resistor
Resistance is inversely proportional to intensity of light
b. Complete the diagram,if the motor works when there is light
PAST YEARS QUESTION
PAST YEARS QUESTION

34. Author : Khairi
c. What is the function of relay,R in the circuit ?
To switch on the secondary circuit
PAST YEARS QUESTION
PAST YEARS QUESTION

35. Author : Khairi
d. Explain how the circuit works.
1. When there is light,resistance of LDR is low
2. Base voltage become high
3. Base current flows and transistor is activated
4. Collector current flows and relay function
5. Relay switch on the secondary circuit
PAST YEARS QUESTION
PAST YEARS QUESTION

36. Author : Khairi
Modify the circuit in the diagram to enable a fan to switch on
automatically when the room is hot.Explain your modification.
PAST YEARS QUESTION
PAST YEARS QUESTION

37. Author : Khairi
Modified circuit as shown in the diagram.
1. When temperature increases,the resistance of thermistor decreased.
2. Potential across R1 becomes high.
3. Base current flows and transistor is activated.
4. Collector current flows and relay switch on the secondary circuit
which contain high voltage power supply and fan connected in series.
PAST YEARS QUESTION
PAST YEARS QUESTION