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NCERT Class XII Chapter
NCERT Class XII Chapter
Semiconductor Electronics
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Question : 18 of 19
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Write the truth table for circuit given in figure below consisting of NOR gates and identify the logic operation (OR, AND, NOT) which this circuit is performing. 
(Hint: A = 0, B = 1 then A and B inputs of second NOR gate will be 0 and hence Y = 1. Similarly work out the values of Y for other combinations of A and B. Compare with the truth table of OR, AND, NOT gates and find the correct one.)
Solution:
Let us find the Boolean expression for the logic circuit. 
So, output Y = = = A + B Hence, the output of given logic circuit shows that logic circuit act as OR gate. Truth Table
| First NOR gate | Second NOR gate | |||||
|---|---|---|---|---|---|---|
| A | B | A + B | X = | A = X | B = X | Y = |
| 0 | 0 | 0 | 1 | 1 | 1 | 0 |
| 0 | 1 | 1 | 0 | 0 | 0 | 1 |
| 1 | 0 | 1 | 0 | 0 | 0 | 1 |
| 1 | 1 | 1 | 0 | 0 | 0 | 1 |
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