PHYSICS INVESTIGATORY PROJECT ON LOGIC GATES

NAMECLASS-12 SECROLL NO-

THIS IS TO CERTIFY THAT OF CLASS XII, SECTION-C, ROLL NOHAS PREPARED A PROJECT ON THE TOPIC”LOGIC GATES”AND HAS SATISFACTORILY COMPLETED THE REQUIRED PHYSICS PROJECT UNDER THE GUIDANCE OF MRS PREETILATA MAM DURING THE SESSION 2015-2016, TOWARDS PARTIAL FULFILLMENT OF CREDIT FOR THE PHYSICS PRACTICAL EVALUATION OF CBSE 2016 AND SUBMITTED SATISFACTORY REPORT AS COMPILED IN THE FOLLOWING PAGES UNDER MY SUPERVISION.

PRINCIPAL/DIRECTOR SIGNATURE SEAL

TEACHER SIGNATURE SIGNATURE

SCHOOL

EXAMINER

I SELECTED THIS PROJECT AS A PART OF MY STUDIES , TITLED”LOGIC GATES”.

AS A GRATITUDE, I CONVEY MY SINCERE THANKS TO MRS ............. MAM WHO WAS A CONSTANT GUIDE DURING THE PERIOD OF STUDIES AND THE PRINCIPAL OF OUR SCHOOL MRS. …………….. WITHOUT WHOSE HELP IT WOULD NOT HAVE BEEN POSSIBLE FOR ME TO COMPLETE THIS PROJECT. I WOULD ALSO LIKE TO THANK THE DIRECTOR OF OUR SCHOOL ……….. FOR HELPING ME.

WE USE THE INTEGRATED CIRCUITS TO CONSTRUCT A LOGIC CIRCUIT AND VERIFY THE TRUTH TABLES OF AND,OR,NOT GATES AND THEIR COMBINATIONS.

1.INTRODUCTION 2.TYPES OF GATE 3.NOT GATE 4.OR GATE 5.AND GATE 6.NAND GATE 7.NOR GATE 8.PROCEDURE

9.OBSERVATION 10.INFERENCE 11.CONCLUSION 12.BIBLIOGRAPHY

INTRODUCTION LOGIC GATES A gate is a digital circuit that follows certain relationship between the input and output voltages. Therefore, they are generally know as logic gates-gates because they control the flow of information.

I.NOT GATE This is the most basic gate, with one input and one output. It produce a ‘1’ output if the input is ‘0’ and vice versa. That is, it produces inverted version of the input as its output. II.OR GATE An ‘OR gate’ has two or more inputs with one output. The output is ‘1’ when either of the inputs are ‘1’ that is if any of the input is high the output is high.

III.AND GATE An‘AND gate’ gas two or more inputs and one output. The output of AND gate is 1 only when the inputs are 1.

THE ‘’NOT GATE’’ The NOT gate is a one input and output logic gate. It combines the input A with the output Y following the Boolean expression. Y=A i.e.Y equals A. The way, the NOT gate gives the output, it is also called invertor. It is represented by the symbol:

It produces 1 output if input is 0 and vice-versa. That is it produces an inverted version of the input at its output.

ELECTRONIC REALIZATION OF NOT GATE In practice a NOT gate can be realized by using transistor as shown in the figure below:

An electronic circuit of a NOT gate using n-p-n transistor is shown in the above figure. The base of the transistor is connected to the input through a resistance Rb and the emitter “E” is earthed. The collector is connected to a 5V battery and the output Y is the voltage at C w.r.t earth. The resistor Rb and Rc are so choosen that if the input is at “0”voltage connected to the collector. The operation can be understood as shown.

When input is earthed, the base of the transistor also gets earthed. The base emitter junction is not forward biased but the base collector junction is reversed biased. As the emitter is “1” the base current is “0”. Hence collector current is also “0”. Under such conditions the transistor is in cut off mode and voltage at C will be +5V w.r.t earth due to battery in the collector circuit. Hence the output Y=1. When the input is connected to the positive terminal of the battery, the base emitter junction gets forward biased. There will be emitter current, base current and collector current . The values of resistors Rb and Rc are so adjusted that in this arrangement a large collector current flows. In this situation, the transistor is said to have gone to saturation state. The voltage drop across Rc due to forward biasing of emitter is just equal to 5V, which is equal and opposite to the potential drop across Rc due to battery in collector circuit. Hence voltage at C=“0” volt. Therefore the output is at “0”level. Thus the operation of the output is based on the following rule.

The output of the NOT gate assumes “1” if both inputs are at “0”level or vice-versa.

THE ‘’OR GATE’’ The OR gate is a two inputs and one output logic gate. It combines the inputs A and B with output Y following the Boolean expression. Y=A+B i.e. Y equals A or B. The OR gate is represented by the symbol:

The output gate has two or more inputs with one output. The output Y is 1 when either input A or input B or both are 1, that is, if any of the input is high, the output is high.

ELECTRONIC REALIZATION OF OR GATE In practice an OR gate can be realized by electronic circuit making use of 2(two) ideal p-n junction diodes D1 and D2. Here negative terminal of the battery is

grounded and corresponds to “0”level and the positive terminal of the battery(i.e.voltage 5V here) corresponds to “1”level. The output Y is at voltage C w.r.t earth. The operation of the OR gate can be understood as follows.

When both A and B are connected to earth(i.e. A-0 and B=0)both the diodes do not conduct and therefore no voltage develops across the resistance R. The voltage at C is “0/” w.r.t earth. Hence the output Y=0. When one of the terminals is connected to earth and the other positive terminal of the battery, the junction diode with “0” input(connected to earth) does not conduct while 5V takes place across resistance R with C at 5V w.r.t earth. Therefore the output Y=1.

When both are connected to the positive terminal of the battery, the two diode become forward biased and they will both conduct. Since connected in parallel voltage drop across R cannot exceed 5V with C at +5Vw.r.t earth. Hence the output is Y=1.

ELECTRONIC REALIZATION OF OR GATE TRUTH TABLE:

DIAGRAM:

THE ‘’AND GATE’’ The AND gate is also a two inputs and one output logic gate. IT combines the inputs A and B with the output Y following the Boolean expression. Y=A.B i.e.Y equals A and B. The AND gate is represented by the symbol

An AND gate has two or more inputs and one output. The output Y of AMD gate is 1 only when input A and B are both 1,that is ,both the inputs should be high than the output will be high. The truth table is given as: Truth table

ELECTRONIC REALIZATION OF AND GATE In practice an AND gate can be realized by electronic circuit making u se of 2 ideal p-n junction diodes D1 and D2 as shown in the figure below

Here negative terminal of the battery is grounded and corresponds to “0”level and the positive terminal of the battery(i.e.voltage 5V here)corresponds to”1”level. The output Y is at voltage C w.r.t earth. The operation of the AND gate can be understood as follows.

When both A and B are connected to earth(i.e. A=0 and B=0)both the diodes gets forward biased and hence conduct. No voltage drop takes place across the diodes. Therefore a voltage drop of 5V takes place across the resistance R with C at “0” potential w.r.t earth. Thus the output Y=0

When one of the two terminals is connected to earth and the other positive terminal of the battery the junction diodes with”0” input(connected to earth) will conduct while the other connected to battery does not conduct. No voltage drop takes place across diode which is earthed. Therefore, a voltage drop of 5V takes place across resistance R having D at +5V and C at 0v w.r.t earth. Now the output Y=0.

When both are connected to the positive terminal of the battery, none of the diodes will conduct. There will be no current through R. Now potential at C=0 potential at D which is +5V w.r.t earth. Hence output Y=1.

Thus the operation of the output is based on the following rule. The output of the AND gate assumes “1” only if all the inputs assume “1”.

ELECTRONIC REALIZATION OF AND GATE DIAGRAM

PROCEDURE The logic gate circuit board is connected to the mains The power of the board is switched on.

For AND gate: The plug wire is put inside the socket named AND gate.

Observations are noted for input having first high and then low value.

Similarly the observations are taken for OR gate and NOT gate. All the observations are recorded.

OBSERVATION

Following are the observations made from the experiment

INFERENCE >For AND gate, when either of the inputs were low, the output was also low. When both inputs were low, output

was low but when both the inputs were high, output was also high. >For OR gate, when either of the inputs were low or high alternatively, the output was high. When both inputs were low, outputs was low but when both the inputs were high, output was also high.

>For NOT gate, when input is high, output is low and vice versa. It inverses the input current.

CONCLUSION

Developing such a project was an enormous task but an enlightening one too. The project work that has perceived in our minds and the final outcome is slightly different. While working on this project we encountered many problems, theoretical as well as practical which were reasonably difficult to manage. This was partly due to my inexperience with the process of experimenting to get the desired result and the approach in which the initial project study was conducted.

Overall I have learnt a lot during the process of development of this project and I have tried my level best to make it as good as possible keeping in minds the time constrain and the project allocated to me.

BIBLIOGRAPHY 1)Comprehensive practical for physics class 12. 2)Internet: www.google.com www.cbseprojects.com