Which is the correct diagram of a half-wave rectifier?

1. 

2. 

3. 

4. 

Zener breakdown takes place if 

(1) Doped impurity is low             

(2) Doped impurity is high
(3) Less impurity in N-part           

(4) Less impurity in P-type

Which one of the following statements is not correct

(1) A diode does not obey Ohm's law

(2) A PN junction diode symbol shows an arrow identifying the direction of current (forward) flow

(3) An ideal diode is an open switch

(4) An ideal diode is an ideal one way conductor

A semiconductor X is made by doping a germanium crystal with arsenic (Z = 33). A second semiconductor Y is made by doping germanium with indium (Z = 49). The two are joined end to end and connected to a battery as shown. Which of the following statements is correct

(1) X is P-type, Y is N-type and the junction is forward biased

(2) X is N-type, Y is P-type and the junction is forward biased

(3) X is P-type, Y is N-type and the junction is reverse biased

(4) X is N-type, Y is P-type and the junction is reverse biased

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

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 the NPN transistor is used as an amplifier:
1. the electrons move from base to collector.
2. the holes move from emitter to base.
3. the electrons move from collector to base.
4. the holes move from collector to emitter.

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