Suppose a 'n'-type wafer is created by doping Si crystal having  \(5\times10^{ 28 }\)atoms/\({ m }^{ 3 }\)with 1 ppm concentration of As.On the surface 200 ppm Boron is added to create \('p'\)region in this wafer. Considering \({ n }_{ i }=1.5\times10^{ 16 }m^{ -3 }\) 
(i) Calculate the densities of the charge carriers in the   \(n\& p\) regions.
(ii) Comment which carriers would contribute largely for the reverse saturation current when diode is reverse biased.

Zener diode is a specially designed \(p-n\) junction diode,in which both \(p-side\) and \(n-side\) of \(p-n\)junction are heavily doped. The zener diode is designed to operate in the reverse break down voltage region continuously without being damaged? Zener diode is used to remove the fluctuations from the given voltage and thereby provides a voltage of constant magnitude (i.e., zener diode is used as voltage regulator).
Read the above paragraph and answer the following questions :
(i) What is the most important use of Zener diode?
(ii) What are the essential conditions for proper working of Zener diode?
(iii) What do you learn from the above study?

Manoj wanted to do social work during vacations.He visited a remote village where there was no electricity. He made up his mind to help the villagers for getting the solar panels. For this he educated the villagers about techonology and uses of solar panels.he requested the villagers to Villagers agreed and applied for the solar panels. They got the same from government at reduced price. When the solar panels started working,the villagers were happy.
Read the passage and answer the following questions:
(i) What is solar panel?
(ii) What is the basic principle of working of a solar cell?
(iii) What are the basic values you assess in Manoj?

Meeta father was driving her to the school.At the traffic signal she noticed that each traffic light was made of many lights instead of a single bulb. When Meeta asked this question to her father's he explained the reason for this.
Answer the following questions based on above information:
(i) What were the values displayed by Meeta and her father?
(ii) What are the tiny lights in traffic signals called and how do these operate? 

(i) Differentiate between three segments of a transistor on the basis of their size and level of doping
(ii) How is a transistor biased to be in active state?
(iii) With the help of necessary circuit diagram, describe briefly how n-p-n transistor in CE configuration amplifies a small sinusoidal input voltage. Write the expression for the AC current gain.

A student of class 12 was trying to understand the concepts of semiconductors and insulators in terms of energy gaps.
(a) How would you explain these concepts to the students ?
(b) What values should we imbibe from this in our daily life ?

Shalini's mother wants to purchase a TV set. Shalini and her mother visited electronic shops to look for some branded TV. The dealer showed them so many TVs such as LCD and LED TVs. Now they were confused which set to buy. Finally after discussing with friends, reading revelent magazines and searching the internet shalini convinced her mother for purchasing LED TV.
(a) What are the values displayed by Shalini ?
(b) What is a LED ?
(c) Which semiconducting material can be used for constructing LED ?

How is a transistors biased to be in active state ?

(i) Using the necessary circuit diagram, draw the transfer characteristics of a base-biased transistor in CE configuration. With the help of these characteristics, explain briefly how the transistor can be used as an amplifier?
(ii) Why are NAND gate called universal gates? Identify the logical operations carried out by the circuit given as below.