2. MRSMPARIT 2
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4. p-n junction (Semiconductor diode)
4
p-type n-type
Positive hole Negative
electron
Symbol
p-n junction
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5. Diode in Forward-biased
5
p-type of the diode is connected
to ………………….
n-type is connected to the
…………………… of the
battery.
Electron moves across the p-n
junction
Current flow through the circuit
Diode is forward biased
+ -
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6. Diode in Reverse-biased
p-type of the diode is connected to
………………….
n-type is connected to the
…………………… of the battery.
Electrons and holes pulled away from
the p-n junction
No Current flow through the circuit
Diode is reverse biased
6
- +
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9. Diode as rectifier
A.C to D.C.
Rectification is a process to convert an alternating current into
a direct current by using a diode.
9
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10. Half-wave rectifier
10
• First half –cycle, diode is forward biased
•Current flow through the circuit
•Second half-cycle, diode is reversed biased
•No current flow
•Diode as half-wave rectifier
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11.
12. Full -wave rectifier
12
• First half –cycle, diode ____________are forward biased
•Current flow through the circuit
•Second half-cycle, diode ___________are forward biased
• Current flow through the circuit
•Diode as full -wave rectifier
To CRO
a
.
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18. store the electrical energy and
give this energy again to the circuit when necessary.
In other words, it charges and discharges the electric charge stored in it.
Other functions of a capacitor are as follows:
◦ It blocks the flow of DC and
◦ permits the flow of AC.
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Capacitor:
19. 19
To CRO
a
To CRO
a.
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As the output voltage increases, the capacitor is charged,
When the output voltage falls back to zero, the capacitor releases its
charge (discharge current)
Steady output voltage is maintained across a resistor
24. extra
The arrow in the symbol indicates the direction of flow of
conventional current in the emitter with forward biasing
applied to the emitter-base junction.
Definition: The transistor is a semiconductor device which
transfers a weak signal from low resistance circuit to high
resistance circuit. The words trans mean transfer
property and istor mean resistance property offered to the
junctions. In other words, it is a switching device which
regulates and amplify the electrical signal likes voltage or
current.
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32. Current Amplifier
Collector current = 1000 x base current
Ic = 1000 x IB
Slow sound amplified by transistor –
become louder sound that spread out
Through the loudspeaker.
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33. When the switch is open, bulb L1 does not light up as the circuit
is _______________
the base current, IB is ____________.
Bulb L2 does not light up although the collector circuit is
complete because the transistor is ___________________ on
and the collector current, Ic is zero.
Close the switch, bulb L1 is dim ∵ RB has a high resistance
The base current, IB is very small.
L2 lights up brightly ∵ the collector current, Ic is larger than IB .
A small IB can produce a minimum base voltage, VBE to turn
on the collector circuit.
The IB can control the flow of the Ic .
This enables the transistor to act as a switch.
The resistance at the base circuit, RB is large to limit the IB
So that the transistor will not become too hot and burn.
34.
35.
36.
37. Light-dependent resistor (LDR) is a type of resistor.
Its resistance changes with the ________________ of light.
The LDR resistance value is ______________ when the light
intensity is low and vice versa.
In the dark, LDR resistance is very ____________________.
38.
39.
40. A thermistor is a resistor.
Its whose resistance changes with its surrounding _______________.
The resistance is ________________ under room temperature conditions
(low temperature).
As the surrounding temperature increases, the resistance becomes
____________ and voltage across the thermistor ________________.
41. Transistor
as a switch
To make the bulb lights up at night,
you have to interchange the position of
LDR and resistor 10 kΩ
Because, at night, resistance of LDR
increases
Then no base current, IB = 0 , no IB flow
to transistor
Therefore , no collector current , Ic =0 ,
no Ic flow to transistor also
Transistor is off
42. Transistor
as a switch
Example :
1. transistor is used as a switch for
streetlamp –
At night , the streetlamps turn on
Daytime, the streetlamps turn off
2. transistor also can be used to
activate fire alarm. Discuss
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