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CBSE NOTES CLASS 12 PHYSICS

CHAPTER 14 SEMICONDUCTORS

Types of substances on the basis of conductivity

Metals on the basis of conductivity

Semiconductors on the basis of conductivity

Insulators on the basis of conductivity

Energy bands in solids

Valence band

Conduction band

Forbidden band

Types of substances on the basis of energy bands

Metals on the basis of energy bands

Insulators on the basis of energy bands

Semiconductors on the basis of energy bands

Types of semiconductors

Elemental semiconductors

Compound semiconductors

Types of semiconductors based on purity

Intrinsic semiconductors

Effect of temperature on conductivity of semiconductors

Extrinsic semiconductor

n-type semiconductor

p-type semiconductor

Conductivity of extrinsic semiconductor

p-n junction

Diffusion of charge

Diffusion current

Depletion region

Drift of charge carriers

Drift current

Potential barrier across p-n junction

Semiconductor diode

Forward bias of p-n junction

Reverse bias of p-n junction

V-I characteristics of a diode

Threshold voltage or cut-in voltage

Dynamic resistance of diode

Application of junction diode as a rectifier

Half wave rectifier

Full-wave rectifier

Centre-tap transformer

Electric filter

Role of capacitor in the filter

Some special type of diodes

Zener diode

Zener diode as voltage regulator

Photodiode

Light emitting diodes (LED)

Photovoltaic devices (Solar cells)

Junction transistor

n-p-n transistor

p-n-p transistor

Transistor emitter

Transistor base

Transistor collector

Transistor in saturation region

Transistor in cut-off region

Transistor in active region

Basic transistor circuit configurations and transistor characteristics

Transistor in common base configuration

Transistor in common emitter configuration

Common emitter transistor characteristics

Input resistance of transistor

Output resistance of transistor

Current amplification factor

Transistor as a device

Transistor as a switch - base-biased CE configuration

Transistor as an amplifier

Amplification of dc voltage

Amplification of ac signal

Feedback amplifier

Transistor oscillator

Working of feedback amplifier

Tank circuit

Digital electronics

Analog signal

Digital signal

Logic gates

NOT gate

OR gate

AND gate

NAND gate

NOR gate

Integrated circuits

Linear or analogue ICs

Digital ICs

CBSE NOTES CLASS 12 PHYSICS

CHAPTER 14 SEMICONDUCTORS

Application of junction diode as a rectifier

The device which restricts the current (or voltage) to only one direction is called rectifier.

A p-n junction diode can be utilized as a rectifier.

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If an alternating voltage is applied across a diode the current flows only in that part of the cycle when the diode is forward biased.

The rectifier circuit, which rectifies only the half-wave, is called a half-wave rectifier.

The secondary of a transformer supplies the desired ac voltage across terminals A and B. When the voltage at A is positive, the diode is forward biased and it conducts. When A is negative, the diode is reverse-biased and it does not conduct. The reverse saturation current of a diode is negligible and can be considered equal to zero for practical purposes.

The reverse breakdown voltage of the diode must be sufficiently higher than the peak ac voltage at the secondary of the transformer to protect the diode from reverse breakdown.

Full-wave rectifier

The circuit using two diodes as in the figure gives output rectified voltage for both the positive as well as negative half of the ac cycle. Hence, it is known as full-wave rectifier. The secondary of the transformer is provided with a centre tapping and so it is called centre-tap transformer.

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Here the p-side of the two diodes is connected to the ends of the secondary of the transformer. The n-sides of the diodes are connected together and the output is taken between this common point of diodes and the midpoint of the secondary of the transformer.

Each diode rectifies only for half the cycle, but the two do so for alternate cycles. Thus, the output between their common terminals and the centre tap of the transformer becomes a full-wave rectifier output.

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Electric filter

The rectified voltage is in the form of pulses of the shape of half sinusoids and does not have a steady value. To get steady dc output a capacitor is connected across the output terminals (parallel to the load RL) or an inductor in series with RL. This arrangement is called filter.

Role of capacitor in the filter

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