Question

(a) A Student wants to use two p-n junction diodes to convert alternating current into direct current. Draw the labelled circuit diagram she would use and Explain how it works.
(b) Give the truth table and circuit symbol for NAND gate.

Answer 1

Hint: If we want to convert the alternating current into direct current, we can use a full wave rectifier. If the both half cycles of the input entering current is rectified, then it is known as full wave rectifier.

Complete answer:
(a) Refer to the below figure1 of a full wave rectifier.
Rectified outputs are given by both diodes for the positive and negative cycles.

The above figure showing the circuit of a fup ll wave rectifier, converts AC to DC.
When voltage is positive with respect to centre tap A, then the voltage for B is negative. Then D1 conducts and D2 does not conduct, because D1 is forward biased and D2 is reverse biased. When there is a negative voltage of A and positive voltage of B, then D1 does not conduct and D2 conducts. Refer to the below figure2 for it.

The above figure (figure 2) shows the output waveforms of the circuit which was shown previously in fig.1, converting AC to DC.

(b) Refer to the truth table and circuit symbol for NAND gate given below.
Logic gate in which the output of the AND gate is given to the input of NOT gate, is called the NAND gate. It is basically the combination of NOT and AND gate. The Boolean expression for the NAND gate is
Here Z is the output and X and Y are the inputs.

In the above diagram, 1 and 2 represent the inputs and 3 represents the output of the NAND gate.
Truth table of a two input NAND gate:

Input 1	Input 2	Output
X	Y	Z
0	0	1
0	1	1
1	0	1
1	1	0

Additional information:
A junction diode can be used as a rectifier. At times when there is a requirement of direct current and we have an alternating current power point, then we need a rectifier. So a rectifier converts alternating current to direct current.

Note:
When a diode is forward biased, then only the current is passed through it which is explained by the voltage-ampere characteristics of the junction diode. The alternating current will pass across the junction diode only in the part where it is forward biased.