Q: The logic operations performed by the given digital circuit is equivalent to:

aligned & Y = Z =( A + B ) ( A B )= A A B + AB B \\ & Y = AB + AB = A B \\ & It is an AND Gate. aligned

Question 1

Identify the correct output signal Y in the given combination of gates for the given inputs A and B shown in the figure.

Accepted Answer

Given circuit can be shown as below Output, Y= ( A )( B ) = A + B =A+B The truth table will be The corresponding input and output waveforms are shown below.

Question 2

Identify the logic gate given in the circuit :

Accepted Answer

Output Y = A B = A + B (ByDe-Morgan Law) Y= A + B This Boolean expression represents OR gate.

Question 3

A reverse biased zener diode when operated in the breakdown region works as

Accepted Answer

In the breakdown region, a reverse biased zener diode works as a voltage regulator.

Question 4

Identify the logic operation performed by the following circuit.

Accepted Answer

Y = A + B = A B = A . B So, Y = A B Therefore gate is AND gate.

Question 5

The logic operations performed by the given digital circuit is equivalent to:

Accepted Answer

aligned & Y = Z =( A + B ) ( A B )= A A B + AB B \ & Y = AB + AB = A B \ & It is an AND Gate. aligned

Question 6

The effect of increase in temperature on the number of electrons in conduction band ( n _ e ) and resistance of a semiconductor will be as:

Accepted Answer

When temperature increases, more electrons excite to conduction band and hence conductivity increases, therefore resistance decreases.

Question 7

For an insulator, the forbidden energy gap is

Accepted Answer

For an insulator, E_ g >3 eV , that is why electron transition from valence band to conduction band is not possible. For semiconductor E_ g is 0.2 eV to 0.3 eV , while for metals E_g>5 eV .

Question 8

In the circuit shown assume the diode to be ideal. When V_i increases from -2 ~V to 6 ~V , the change in current is (in mA )

Accepted Answer

l_ initial =0 for V_i +1 ~V This diode conduct only beyond V_i=+1 ~V I_ final = 5 250 =0.02 ~A So, change in I=0.02 ~A =20 ~mA

Question 9

In the following circuit the equivalent resistance between X and Y is ......

Accepted Answer

According to the given figure X is at lower potential w.r.t Y. Hence, both diodes are in reverse biasing, so, equivalent circuit can be redrawn as follows Equivalent resistance between X and Y R_ eq =8+2+6=16

Question 10

A transistor is connected in common-emitter (CE) configuration. The collector supply is 8 ~V and the voltage drop across a resistor is 500 in the collector circuit is 0.6 ~V . If the current gain fact

Accepted Answer

Given, V_ C C =8 ~V Voltage drop, V_0= I_C R_L=0.6 ~V Load Resistor, R_L=500 Gain factor, =0.96 = 1- = 0.96 1-0.96 =24 Now, V_0= I_C R_L 0.6= I_C 500 I_C= 0.6 500 =1.2 10^ -3 ~A Now, = I_C I_B Base current I_B= I_C = 1.2 10^ -3 24 =5 10^ -5 =50 10^ -6 I_B=50 A

Question 11

A zener diode of voltage V _ Z (=6 ~V ) is used to maintain a constant voltage across a load resistance R _ L (=1000 ) by using a series resistance R_ s (=100 ). If the e.m.f. of source is E (=9 ~V ),

Accepted Answer

Here, E=9 ~V ; V _ z =6 ; R _ L =1000 and R _ s =100 , Potential drop across series resistor V = E - V _ Z =9-6=3 ~V Current through series resistance R_ S is I = V R = 3 100 =0.03 ~A Current through load resistance R_ L is I _ L = V _ Z R _ L = 6 1000 =0.006 ~A Current through Zener diode is I _ Z = I - I _ L =0.03-0.006=0.024 amp . Power dissipated in Zener diode is P _ Z = V _ Z I _ Z =6 0.024=0.144 Watt

Question 12

The I - V characteristics shown in figure represents

Accepted Answer

The figure is showing I - V characteristics of non ohmic or non linear conductors.

Semiconductors — Previous Year Questions & Solutions