Solutions of chapter 14. Semiconductor Electronics

1

The conductivity of a semiconductor increases with increase in temperature because

2

2 In Fig. 14.1, V_o is the potential barrier across a p-n junction, when no battery is connected across the junction

3

In Fig. 14.2, assuming the diodes to be ideal,

4

A 220 V A.C. supply is connected between points A and B (Fig. 14.3). What will be the potential difference V across the capacitor?

5

Hole is

6

The output of the given circuit in Fig. 14.4.

7

In the circuit shown in Fig. 14.5, if the diode forward voltage drop is 0.3 V, the voltage difference between A and B is

8

Truth table for the given circuit (Fig. 14.6) is

9

When an electric field is applied across a semiconductor

10

Consider an npn transitor with its base-emitter junction forward biased and collector base junction reverse biased. Which of the following statements are true?.

11

Figure 14.7 shows the transfer characteristics of a base biased CE transistor. Which of the following statements are true?

12

In a npn transistor circuit, the collector current is 10mA. If 95 per cent of the electrons emitted reach the collector, which of the following statements are true?

13

In the depletion region of a diode

14

What happens during regulation action of a Zener diode?

15

To reduce the ripples in a rectifier circuit with capacitor filter

16

The breakdown in a reverse biased p–n junction diode is more likely to occur due to

17

Why are elemental dopants for Silicon or Germanium usually chosen from group XIII or group XV?

18

Sn, C, and Si, Ge are all group XIV elements. Yet, Sn is a conductor, C is an insulator while Si and Ge are semiconductors. Why?

19

Can the potential barrier across a p-n junction be measured by simply connecting a voltmeter across the junction?

20

Draw the output waveform across the resistor (Fig.14.8).

21

The amplifiers X, Y and Z are connected in series. If the voltage gains of X, Y and Z are 10, 20 and 30, respectively and the input signal is 1 mV peak value, then what is the output signal voltage (peak value)

(i) if dc supply voltage is 10V?

(ii) if dc supply voltage is 5V?

22

In a CE transistor amplifier there is a current and voltage gain associated with the circuit. In other words there is a power gain. Considering power a measure of energy, does the circuit violate conservation of energy?

23

(a)

(b)

(i) Name the type of a diode whose characteristics are shown in Fig. 14.9 (A) and Fig. 14.9(B).

24

Three photo diodes D1, D2 and D3 are made of semiconductors having band gaps of 2.5eV, 2eV and 3eV, respectively. Which ones will be able to detect light of wavelength

25

If the resistance R₁ is increased (Fig.14.10), how will the readings of the ammeter and voltmeter change?

26

Two car garages have a common gate which needs to open automatically when a car enters either of the garages or cars enter both. Devise a circuit that resembles this situation using diodes for this situation.

27

How would you set up a circuit to obtain NOT gate using a transistor?

28

Explain why elemental semiconductor cannot be used to make visible LEDs.

29

Write the truth table for the circuit shown in Fig.14.11. Name the gate that the circuit resembles.

30

A Zener of power rating 1 W is to be used as a voltage regulator. If zener has a breakdown of 5V and it has to regulate voltage which fluctuated between 3V and 7V, what should be the value of Rs for safe operation (Fig.14.12)?

31

If each diode in Fig. 14.13 has a forward bias resistance of 25 �Ω and infinite resistance in reverse bias, what will be the values of the current I₁, I₂, I₃ and I₄?

32

In the circuit shown in Fig.14.14, when the input voltage of the base resistance is 10V, V_be is zero and V_ce is also zero. Find the values of I_b, I_c and β.

33

Draw the output signals C₁ and C₂ in the given combination of gates (Fig. 14.15).

34

Consider the circuit arrangement shown in Fig 14.16 (a) for studying input and output characteristics of n-p-n transistor in CE configuration.

Select the values of R_B and R_C for a transistor whose V_BE = 0.7 V, so that the transistor is operating at point Q as shown in the characteristics shown in Fig. 14.16 (b).

Given that the input impedance of the transistor is very small and V_CC = V_BB = 16 V, also find the voltage gain and power gain of circuit making appropriate assumptions.

35

Assuming the ideal diode, draw the output waveform for the circuit given in Fig. 14.17. Explain the waveform.

36

Suppose a ‘n’-type wafer is created by doping Si crystal having 5 × 10²⁸ atoms/m³ with 1ppm concentration of As. On the surface 200 ppm Boron is added to create ‘P’ region in this wafer. Considering n_i = 1.5 × 10¹⁶ m^–3, (i) Calculate the densities of the charge carriers in the n & p regions. (ii) Comment which charge carriers would contribute largely for the reverse saturation current when diode is reverse biased.

37

An X-OR gate has following truth table:

It is represented by following logic relation

Build this gate using AND, OR and NOT gates.

38

Consider a box with three terminals on top of it as shown in Fig.14.18 (a):

Three components namely, two germanium diodes and one resistor are connected across these three terminals in some arrangement.

A student performs an experiment in which any two of these three terminals are connected in the circuit shown in Fig. 14.18 (b).

The student obtains graphs of current-voltage characteristics for unknown combination of components between the two terminals connected in the circuit.

The graphs are

(i) when A is positive and B is negative