Physics Class 12 NCERT Solutions: Chapter 14 Semiconductor Electronics Materials Devices and Simple Circuits Part 5

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DeMorgan's Theorems

DeMorgan's Theorems

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Q: 18. Write the table for circuit given in Figure below consisting of NOR gates and identify the logic operation which this circuit is performing

Q 18 Circuit of the NOR Gates

Q 18 Circuit of the nor Gates

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(Hint: then A and B inputs of second NOR gate will be and hence. Similarly work out the values of Y for other combinations of A and B. Compare with the truth table of gates and find the correct one.)

Answer:

A and B are the inputs of the given circuit. The output of the first NOR gate is. It can be observed from the following figure that the inputs of the second gate become the output of the first one.

Q 18 1 Circuit of output of the First NOR Gates and Input of …

Q 18 1 Output of First nor Gates and Input of the 2 nor Gate

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Hence, the output of the combination is given as:

The truth table for this operation is given as:

Q_18_2_Truth Table of OR Gate

A

B

0

0

0

0

1

1

1

0

1

1

1

1

This is the truth table of an OR gate. Hence, this circuit functions as an OR gate.

Q: 19. Write the truth table for the circuits given in Figure consisting of NOR gates only. Identify the logic operations (OR, AND, NOT) performed by the two circuits.

Q 19 Circuits of NOR Gates and Identify the logic operations …

Q 19 Circuits of nor Gates and Logic Operations (Or, and, NO …

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Answer:

(A) A acts as the two inputs of the NOR gate and Y is the output, as shown in the following figure. Hence, the output of the circuit is

Q 19 A Circuit of NOR Gate

Q 19 a Circuit of nor Gate

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Output,

The truth table for the same is given as:

Q_19_2_Truth Table of NOT Gate

A

This is the truth table of a NOT gate. Hence, this circuit functions as a NOT gate.

(B) A and B are the inputs and Y is the output of the given circuit. By using the result obtained in solution (A), we can infer that the outputs of the first two NOR gates are, as shown in the following figure.

Q 19 3 The Inputs for the Last NORE gate

Q 19 3 the Inputs for the Last nor Gate

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are the inputs for the last NOR gate. Hence, the output for the circuit can be written as:

The truth table for the same can be written as:

Q_19_4_Truth Table of AND Gate

A

B

0

0

0

0

1

0

1

0

0

1

1

1