A Zener diode, having breakdown voltage equal to $15$ V, is used in a voltage regulator circuit, as shown in the figure. The current through the diode is:

                      
1. $10$ mA
2. $15$ mA
3. $20$ mA
4. $5$ mA

Which one of the following statement is false?

(1) Pure Si doped with trivalent impurities gives a p-type semiconductor 

(2) Majority carries in a n-type semiconductor are holes

(3) Minority carries in a p-type semiconductor are electrons

(4) The resistance of intrinsic semiconductor decreases with increase of temperature 

The device that can act as a complete electronic circuit is

1. Junction diode

2. Integrated circuit

3. Junction transistor

4. Zener diode

The following figure shows a logic gate circuit with two inputs A and B and the output Y. The voltage waveforms of A, B and Y are as given

The logic gate is 

1. $\mathrm{NOR}$ gate                                                 

2. $\mathrm{OR}$ gate

3. $\mathrm{AND}$ gate                                                 

4. $\mathrm{NAND}$gate

For transistor action:

Which of the following pairs of statements is correct?
1. (d) and (a)
2. (a) and (b)
3. (b) and (c)                                       
4. (c) and (d)

A p-n photodiode is fabricated from a semiconductor with a band gap of $2.5 \mathrm{eV}.$ It can detect a signal of wavelength 

1. $6000 \stackrel{\circ }{\mathrm{A}}$                                   
2. $4000 \mathrm{nm}$
3. $6000 \mathrm{nm}$                                 
4. $4000 \stackrel{\circ }{\mathrm{A}}$

The symbolic representation of four logic gates 

                           (i)                                                                              (ii)

                           (iii)                                                                              (iv)

The logic symbols for $\mathrm{OR},$ $\mathrm{NOT}$ and $\mathrm{NAND}$ gates are respectively

1. (iii), (iv), (ii)                                           
2. (iv), (i), (iii)
3. (iv), (ii), (i)                                             
4. (i), (iii), (iv) 

A transistor is operated in common-emitter configuration at $V_c=2volt$ such that a change in the base current from 100 $\mu A$ to 200 $\mu A$ produces a change in the collector current from 5 mA to 10 mA. The current gain is 

1. 75                               
2. 100
3. 150                             
4. 50