#### Topics

1.The V-I characteristic of a silicon diode is shown in the figure. Calculate the resistance of the diode at

## Considering the diode characteristics as a straight line between I = 10mA to I = 20 mA passing through the origin, we can calculate the resistance using Ohm's law.
(a) From the curve, at I = 20 mA, V = 0.8 V, I = 10 mA, V - 0.7V (b) From the curve at 2.In a Zener regulated power supply a Zener diode with Vz =6.0 V is used for regulation.  The load current is to be 4.0mA and the unregulated input is 10.0V.  What should be the value of series resistor Rs?

The value of Rs should be such that the current through the Zener diode (Iz )is much larger than the load current (IL ).  This is to have good load regulation.
Let us choose Iz =5IL , i.e., Iz = 20 mA.  The total current through Rs is, therefore, 24 mA.  The voltage drop across Rs. is 10.0-6.0 = 4.0 V.  This gives Rs = 4.0 V / The nearest value of carbon resistor is 150 Ω is appropriate.  Slight variation in the value of the resistor does not matter, what is important is that the current Iz should be sufficiently larger than IL.
3. (a)The number of electron-hole pairs in an intrinsic semiconductor is Calculate the number of electron-hole pairs at 227o C.  Given that Boltzmann constant is (b)  If this semiconductor is doped by a donor impurity such that the number of conduction electron becomes calculate the number of holes at 27o C.  Also approximately calculate the dopant concentration.

(a) 4. In half wave rectification, what is the output frequency if the input frequency is 50 Hz?  What is the output frequency of a full wave rectifier for the same input frequency?

Output frequency in Half Wave Rectifier : 50 Hz.
Output frequency in Full Wave Rectifier : 100 Hz.

5.For a CE transistor amplifier, the audio signal voltage across the collector resistance of 2 k is 2 V.  Current amplification factor of the transistor is 100.  Find the input signal voltage and base current if the resistance is 1 k . 6.You are given two circuits as shown, which consist of NAND gates. Identify the logic operation carried out by the two circuits. The truth table for first circuit : If we remove the intermediate output Y', the overall result stands for the AND gate. Hence, the circuit is an equivalent of AND gate.  The truth table for second circuit : If we remove the intermediate output the overall result stands for the OR gate.
This can be represented as Y = A + B
Hence, the circuit is an equivalent of OR gate. 7. A transistor has a current amplification factor (current gain) of 50.  In a CE - amplifier circuit, the collector resistance is chosen as 50 k and the input resistance is 1 k .  Calculate the output voltage if input voltage is 0.01 V. 8.The number of silicon atoms per . This is dipped simultaneously with atoms per m3 of Arsenic and atoms of Indium. Calculate the number of electrons and holes. . Is the material n-type or p-type? 9.In an intrinsic semiconductor the energy gap Eg is 1.2 eV. Its hole mobility is much smaller than electron mobility and independent of temperature.  What is the ratio between conductivity at 600 K and that at 300 K?  Assume that the temperature dependence of intrinsic carrier concentration ni is given by  Paid Users Only!
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