14. Semiconductor Electronics : Materials , Devices and Simple Circuits

CBSE Class 12 Chapter 14. Semiconductor Electronics : Materials , Devices and Simple Circuits

Chapter 14. Semiconductor Electronics : Materials , Devices and Simple Circuits

Class 12 Physics Chapter 14. Semiconductor Electronics : Materials , Devices and Simple Circuits Exercise Questions and Answers :

14.1 In an -type silicon, which of the following statement is true:

(a) Electrons are majority carriers and trivalent atoms are the dopants.

(b) Electrons are minority carriers and pentavalent atoms are the dopants.

(d) Holes are majority carriers and trivalent atoms are the dopants.

14.2 Which of the statements given in Exercise 14.1 is true for -type semiconductos.

14.3 Carbon, silicon and germanium have four valence electrons each. These are characterised by valence and conduction bands separated by energy band gap respectively equal to , and . Which of the following statements is true?

(a)

(b)

(c)

(d)

14.4 In an unbiased - junction, holes diffuse from the -region to -region because

(a) free electrons in the -region attract them.

(b) they move across the junction by the potential difference.

(d) All the above.

14.5 When a forward bias is applied to a - junction, it

(a) raises the potential barrier.

(b) reduces the majority carrier current to zero.

(d) None of the above.

14.6 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.

14.7 A - photodiode is fabricated from a semiconductor with band gap of 2.8 eV. Can it detect a wavelength of 6000 nm?

Class 12 Physics Chapter 14. Semiconductor Electronics : Materials , Devices and Simple Circuits Additional Exercise Questions and Answers :

14.8 The number of silicon atoms per is . This is doped simultaneously with atoms per of Arsenic and per atoms of Indium. Calculate the number of electrons and holes. Given that . Is the material -type or -type ?

14.9 In an intrinsic semiconductor the energy gap is 1.2eV. Its hole mobility is much smaller than electron mobility and independent of temperature. What is the ratio between conductivity at 600K and

that at 300K? Assume that the temperature dependence of intrinsic carrier concentration is given by , where is a constant.

14.10 In a - junction diode, the current can be expressed as where is called the reverse saturation current, is the voltage across the diode and is positive for forward bias and negative for reverse bias, and is the current through the diode, is the Boltzmann constant ( eV/K) and T is the absolute temperature. If for a given diode A and T = 300 K, then

(a) What will be the forward current at a forward voltage of 0.6 V?

(b) What will be the increase in the current if the voltage across the diode is increased to 0.7 V?

(d) What will be the current if reverse bias voltage changes from 1 V to 2 V?

14.11 You are given the two circuits as shown in Fig. 14.36. Show that circuit (a) acts as OR gate while the circuit (b) acts as AND gate.

FIGURE 14.36

14.12 Write the truth table for a NAND gate connected as given in Fig. 14.37.

FIGURE 14.37

Hence identify the exact logic operation carried out by this circuit.

14.13 You are given two circuits as shown in Fig. 14.38, which consist of NAND gates. Identify the logic operation carried out by the two circuits.

FIGURE 14.38

14.14 Write the truth table for circuit given in Fig. 14.39 below consisting of NOR gates and identify the logic operation (OR, AND, NOT) which this circuit is performing.

FIGURE 14.39

(Hint: A = 0, B = 1 then A and B inputs of second NOR gate will be 0 and hence Y=1. Similarly work out the values of Y for other combinations of A and B. Compare with the truth table of OR, AND, NOT gates and find the correct one.)

14.15 Write the truth table for the circuits given in Fig. 14.40 consisting of NOR gates only. Identify the logic operations (OR, AND, NOT) performed by the two circuits.

FIGURE 14.40