In a sample of semiconductor mobilities of electrons and holes are 24 × 10 3 cm 2 V - 1 s - 1 and 0 . 2 × 10 3 cm 2 V - 1 s - 1 respectively. If the density of electrons is 0 . 8 × 10 14 cm - 3 and that of holes is 0 . 4 × 10 14 cm - 3 . Find the nature of the semi-conductor and its conductivity.

Given the mobility of the electron V e = 24 × 10 3 c m 2 V - 1 s - 1 = 24 × 10 3 × 10 - 4 c m 2 V - 1 s - 1 = 24 × 10 - 1 m 2 V - 1 s - 1 . Mobility of holes V h = 0 . 2 × 10 3 cm 2 V - 1 s - 1 = 0 . 2 × 10 3 × 10 - 4 cm 2 V - 1 s - 1 = 0 . 2 × 10 - 1 m 2 V - 1 s - 1 The density of electrons n e = 0 . 8 × 10 14 cm - 3 . The density of holes n h = 0 . 4 × 10 14 cm - 3 As n e > n h the semiconductor is n -type ...........................................(1) As the conductivity is given by, σ = e ( n e v e + n h V h ) , substituting the values, we get, σ = 1 . 6 × 10 - 19 ( 0 . 8 × 10 20 × 24 × 10 - 1 + 04 × 10 20 × 0 . 2 × 10 - 1 ) Or σ = 30 . 84 ohm meter .

What is a rectifier? Explain the working of p-n junction diode as a full-wave rectifier with the help of a suitable circuit diagram.

A device that converts an a.c. signal to a d.c signal is called a rectifier The p-n junction is used as a full-wave rectifier are as shown in the figure. V The p-n junction is used as a full-wave rectifier are as shown in the figure. An AC input is applied to the primary of the transformer in the first half cycle of a.c, end A of secondary centre taping transformer is +ve & end B is -ve diode D 1 is in forward bias & hence current flows but diode D 2 is reverse bias & hence current does not flow. in the next half-cycle of AC end A of the secondary centre taping transformer is -ve & end B is +ve diode D 1 is reverse bias & hence current does not flow but diode D 2 is in forward bias & hence current flows this process will continue & hence output d.c.signal is obtained across the load resistance.

Write truth table of AND gate.

The truth table of AND gate is as follows: The table used to represent the boolean expression of a logic gate function is commonly called a Truth Table. A logic gate tru th table shows each possible input combination to the gate or circuit with the resultant output depending upon the combination of these input(s). A B Y 0 0 0 1 0 0 0 1 1 1 1 1

Why does the thickness of the depletion layer of p - n junction increase in reverse biassing? Draw the circuit diagram of reverse biassing.

When the p - n junction is reversed biassed, the positive terminal of the external battery is connected to the n-side of the p - n junction and its negative terminal to p -side of p - n junction. The positive terminal of the external battery attracts the majority carrier electrons from the n region and its negative terminal attract the majority carrier holes from the p-region. Due to it, the majority charge carriers move away from the junction. This increases the width of the depletion layer. The circuit arrangement of reversed biassing: