Which is the wrong statement in following sentences?

A device in which P and N-type semiconductors are used is more useful then a vacuum type because 

(1) Power is not necessary to heat the filament

(2) It is more stable

(3) Very less heat is produced in it

(4) Its efficiency is high due to a high voltage across the junction

In the diagram, the input is across terminals A and C and the output is across terminals B and D, then the output is:

(1) Zero                                                              

(2) Same as input

(3) Full wave rectifier  

(4) Half wave rectifier

The current through an ideal PN-junction shown in the following circuit diagram will be

(1) Zero

(2) 1 mA

(3) 10 mA

(4) 30 mA

If a full wave rectifier circuit is operating from 50 Hz mains, the fundamental frequency in the ripple will be

(1) 50 Hz                           

(2) 70.7 Hz

(3) 100 Hz                         

(4) 25 Hz

A diode having potential difference 0.5 V across its junction which does not depend on current, is connected in series with resistance of 20 $\mathrm{\Omega }$ across source. If 0.1 A passes through resistance then what is the voltage of the source

1. 1.5 V                     

2. 2.0 V

3. 2.5 V                     

4. 5 V

When NPN transistor is used as an amplifier

(1) Electrons move from base to collector

(2) Holes move from emitter to base

(3) Electrons move from collector to base

(4) Holes move from collector to emitter

The phase difference between input and output voltages of a CE circuit is 

(1) 0$°$                         

(2) 90$°$ 

(3) 180$°$                      

(4) 270$°$ 

The emitter-base junction of a transistor is …… biased while the collector-base junction is ……. biased.
1. reverse, forward                       

2. reverse, reverse

3. forward, forward                       

4. forward, reverse

In an NPN transistor the collector current is 24 mA. If 80% of electrons reach collector its base current in mA is

1. 36                       2. 26
3. 16                       4. 6

If $\mathrm{\alpha }$ = 0.98 and current through emitter ${\mathrm{i}}_{\mathrm{e}}$ = 20 mA, the value of $\mathrm{\beta }$ is 
(a) 4.9                  (b) 49
(c) 96                   (d) 9.6