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Introduction A gate is defined as a digital circuit which follows some logical relationship between the input and output voltages. It is a digital circuit which either allows a signal to pass through as stop, it is called a gate. The logic gates are building blocks at digital electronics. They are used in digital electronics to change on voltage level (input voltage) into another (output voltage) according to some logical statement relating them. A logic gate may have one or more inputs, but it has only one output. The relationship between the possible values of input and output voltage is expressed in the form of a table called truth table or table of combinations. Truth table of a Logic Gates is a table that shows all the input and output possibilities for the logic gate.

George Boole in 1980 invented a different kind of algebra

based on binary nature at the logic, this algebra of logic

called BOOLEAN ALGEBRA. A logical statement can have

only two values, such as HIGH/LOW, ON/OFF,

CLOSED/OPEN, YES/NO, RIGHT/WRONG, TRUE/FALSE,

CONDUCTING/NON-CONDUCTING ,etc. The two values of

logic statements one denoted by the binary number 1 and

0. The binary number 1 is used to denote the high value.

The logical statements that logic gates follow are called

Boolean expressions.

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PRINCIPLE

Any Boolean algebra operation can be associated with

inputs and outputs represent the statements of Boolean

algebra. Although these circuits may be complex, they may

all be constructed from three basic devices. We have three

different types of logic gates .These are the AND gate, the

OR gate and the NOT gate.

LOGIC STATES

1 0

HIGH LOW

ON OFF

CLOSE OPEN

RIGHT WRONG

TRUE FALSE

YES NO

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OR GATE Components:

Two ideal p-n junction diode (D1 and D2).

Theory and Construction:

An OR gate can be realize by the electronic circuit, making use of two diodes D1 and D2 as shown in the figure. Here the negative terminal of the battery is grounded and corresponds to the 0 level, and the positive terminal of the battery (i.e. voltage 5V in the present case) corresponds to level 1. The output Y is voltage at C w.r.t. earth.

The following interference can be easily drawn from the working of electrical circuit is: a) If switch A & B are open lamp do not glow (A=0, B=0), hence Y=0. b) If Switch A open B closed then (A=0, B=1) Lamp glow, hence Y=1. c) If switch A closed B open then (A=1, B=0) Lamp glow, hence Y=1. d) If switch A & B are closed then (A=1, B=1) Lamp glow, hence Y=1.

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Truth Table:

Input A Input B Output Y

0 0 0 1 0 1 0 1 1 1 1 1

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AND GATE Components:

Two ideal p-n junction diode (D1 and D2), a resistance R.

Theory and Construction:

An AND gate can be realize by the electronic circuit, making use of two diodes D1 and D2 as shown in the figure. The resistance R is connected to the positive terminal of a 5V battery permanently. Here the negative terminal of the battery is grounded and corresponds to the 0 level, and the positive terminal of the battery (i.e. voltage 5V in the present case) corresponds to level 1. The output Y is voltage at C w.r.t. earth.

The following conclusions can be easily drawn from the working of electrical circuit:

a) If both switches A&B are open (A=0, B=0) then lamp will not glow, hence Y=0.

b) If Switch A closed & B open (A=1, B=0) then Lamp will not glow, hence Y=0. c) If switch A open & B closed (A=0, B=1) then Lamp will not glow, hence Y=0. d) If switch A & B both closed (A=1, B=1) then Lamp will glow, hence Y=1.

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Truth Table:

Input A Input B Output Y

0 0 0 1 0 0 0 1 0 1 1 1

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NOT GATE Components:

An ideal n-p-n transistor.

Theory and Construction:

A NOT gate cannot be realized by using diodes. However an electronic circuit of NOT gate can be realized by making use of a n-p-n transistor as shown in the figure. The base B of the transistor is connected to the input A through a resistance Rb and the emitter E is earthed. The collector is connected to 5V battery. The output Y is voltage at C w.r.t. earth.

The following conclusion can be easily drawn from the working of the

electrical circuit:

a) If switch A is open (i.e. A=0), the lump will glow, hence Y=1. b) If Switch A is closed (i.e. A=1), the lump will not glow, hence Y=0.

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Truth Table:

Input A Output Y

0 1

1 0

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NOR GATE Components:

Two ideal p-n junction diode (D1 and D2), an ideal n-p-n transistor.

Theory and Construction:

If we connect the output Y’ of OR gate to the input of a NOT gate the gate obtained is called NOR. The output Y is voltage at C w.r.t. earth.

In Boolean expression, the NOR gate is expressed as Y=A+B, and is being read as ‘A OR B negated’. The following interference can be easily drawn from the working of electrical circuit is: a) If Switch A & B open (A=0, B=0) then Lamp will glow, hence Y=1. b) If Switch A closed & B open (A=1, B=0) then Lamp will not glow, hence Y=0. c) If Switch A open & B close (A=0, B=1) then Lamp will not glow, hence Y=0. d) If switch A & B are closed then (A=1, B=1) Lamp will not glow, hence Y=0.

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Truth Table:

Input A Input B Output Y 0 0 1 1 0 0 0 1 0 1 1 0

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NAND GATE Components:

Two ideal p-n junction diode (D1 and D2), a resistance R, an ideal n-p-n

transistor.

Theory and Construction:

If we connect the output Y’ of AND gate to the input of a NOT gate the gate obtained is called NAND. The output Y is voltage at C w.r.t. earth.

In Boolean expression, the NAND gate is expressed as Y=A.B, and is being read as ‘A AND B negated’. The following interference can be easily drawn from the working of electrical circuit: a) If Switch A & B open (A=0, B=0) then Lamp will glow, hence Y=1. b) If Switch A open B closed then (A=0, B=1) Lamp glow, hence Y=1. c) If switch A closed B open then (A=1, B=0) Lamp glow, hence Y=1. d) If switch A & B are closed then (A=1, B=1) Lamp will not glow, hence Y=0.

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Truth Table:

Input A Input B Output Y 0 0 1 1 0 1 0 1 1 1 1 0

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POLARISATION OF

LIGHT A light beam which has all of the wave oscillations in a single

plane of space is said to have total plane polarization. Light

with an equal amount of oscillations in all directions is

unpolarized. The “in-between” case is one where there is

partially polarized light. Most sources of light in nature to not

emit polarized light. To do so would require the oscillating

electric charges that produce it to move in unison in the same

direction.

For a plane polarized beam. We can always subdivide the Similarly, an unpolarized beam could be

amplitude as the vector sum of two perpendicular represented this way

components. We will see that this is useful, because we

can usually choose how to do the subdivision to solve a

particular problem. If we could “see” the amplitudes for

a beam coming directly toward us, it might look like this.

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TRANSMISSION

Polarizing filters, such as those in Polaroid sunglasses, are

designed to allow only one plane of light through (although they

are not 100% effective, they can be pretty close to that value).

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In each case shown, the second filter allows only that component that lies in

the “transmission direction” though. In (a), all of the amplitude is in the

transmission direction, so it all gets through. In (b), none of the amplitude is

in the transmission direction, so none gets through. In (c), the transmission

direction is rotated 45° to the direction of the amplitude, so some of the

light gets through.

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POLARISATION BY

REFLECTION

Light striking a surface, such as a piece of glass, the

surface of water, etc., can be both transmitted through the

surface and reflected from it. The amount that is

transmitted or reflected, and its polarization, depends on

the angle of incidence and the material it is hitting.

Parallel component: The amplitude runs along the plane

of the surface as it hits

Perpendicular component: The amplitude is in the plane

of incidence

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For the parallel component, there is always some reflection,

even when the angle of incidence θ1 is 0. At higher angles

of incidence, the reflectance increases until it reaches

100% at grazing incidence.

The perpendicular component has a more complex

behavior. It begins at the same reflectance as the parallel

beam at θ1=0, slowly decreases to 0 reflectance at some

specific angle, then increases.

The angle where the reflection goes to 0% (and the

transmission to 100%) is called Brewster’s Angle. and it

depends on the index of refraction of the material.

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POLARISATION BY

SCATTERING

The scattering of light off air molecules produces linearly

polarized light in the plane perpendicular to the incident

light. The scatterers can be visualized as tiny antennae

which radiate perpendicular to their line of oscillation. If

the charges in a molecule are oscillating along the y-axis, it

will not radiate along the y-axis. Therefore, at 90° away

from the beam direction, the scattered light is linearly

polarized. This causes the light which undergoes Rayleigh

scattering from the blue sky to be partially polarized.

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OPTICAL ACTIVITY

Some crystals and organic materials have a twisted

molecular structure that produces another interesting

effect: “optical activity”.

Here, the plane of polarization rotates as the beam passes

through the material, and it can rotate different amounts

for different wavelengths. This phenomenon is useful for

analyzing mineral crystals and organic pharmaceuticals.

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POLARISED LIGHT IN

THE ENVIRONMENT

Due to the optical properties of various natural and

artificial materials, the effects of polarized light are all

around us. In addition to Haidinger’s Brush, we often use

polarized filters in the form of sunglasses to cut glare due

to reflected sunlight. It is also used to darken the sky in

photography, remove glare from subjects behind windows,

etc.

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BIBLIOGRAPHY

ENCARTA ENCYCLOPEDIA

BRITANICCA ENCYCLOPEDIA

www.googLE.CO.IN

WWW.ANSWERS.COM

WWW.WIKIPEDIA.COM

WWW.STUDYPHYSICS.CA

WWW.PHYSICSCLASSROOM.COM

LOGIC GATES

POLARISATION OF LIGHT

ACKNOWLEDGEMENT

I take this opportunity to express my profound sense of gratitude and respect to all those who helped me throughout this venture.

I owe my regard to Mr. R.S. Rana, Principal of K.V. NOIDA , for his cooperation and valuable support and for giving me the opportunity to undertake this project work and providing the necessary infrastructure.

I would like to express my heartfelt thanks to my revered

teacher and guide Mr. Ajab Singh for his valuable guidance, encouragement and support throughout my studentship under him at the institute. This project is his visualization and owes a lot of its functionality to him.

Last but not the least; I owe my overwhelming gratitude

to my family and friends who gave me constant support and motivation to continue with this endeavour.

RITESH KUMAR XII G

INDEX

Serial No. Contents

Page no.

1 Introduction 1

2 Principle 2

3 OR Gates 3-4

4 AND Gates 5-6

5 NOT gate 7-8

6 NOR Gate 9-10

7 NAND Gate 11-12

8 Polarisation of light

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9 Transmission 14-15

10 Polarisation by reflection

16-17

11 Polarisation by scattering

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12 Optical activity 19

13 Polarised light in the environment

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14 Bibliography 21