JUNE 2015 ELECTRONIC SCIENCE PAPER WITH ANSWER KEY

Check out answer keys of electronic science paper held on 28th June here(Paper 2 and Paper 3)

https://www.facebook.com/groups/1401072580199769/

One good thing to remember while preparing for UGC NET is Comparison Of Various Logic Families and Microwave Frequency band.

Ans C

now int, char and double are basically datatypes in C language.lets understand what each of them mean

A] Int is used to define integers.

int i;

i = 5;

here i is defined as integer (basically it is a memory location allocated to store integer value) and assigned a value 5.

  

B] char is used to define character.

char let ; 

let = 'x';

C] double use to define floating point numbers (e.g = 5.46  , 6.81)

double j  ;

j = 4.5;

Now consider above question we have,

  int i = 3;

  int j = 7;

  double  f = 5.5 ;

double g = 4.5;

char ch = 'T' ;

• ||  means OR  
• && means AND   
• == means Equal to

Consider option A

 (i < = 5 ) && ( ch == 'T')

for above eq. to give true value both expression should be true lets check them.

as i =3  it is less than 5 so first expression is indeed true.

now ch = 'T' is also given in question so it is also true as both expressions are true above equation will give vale  TRUE.

Consider option B

(i < 8 )  || ( ch = ' L')

for above eq. to give true value one expression should be atleast true lets check them.

as i =3  it is less than 8 so first expression is indeed true.

so above equation gives TRUE value.

Consider option C

(f > 6)  || (i*j < 15)

as f = 5.5 first expression is false

i* j = 16.5  which is greater than 15 so this expression is also false.

so the value of equation is FALSE

So option C is correct option.

Ans . B

A]  Current density (J ) is given by

J = p* Vd          ----------------------- (1)

where,
p = charge density
Vd = drift velocity


B] Charge density is basically no. of charges present inside the material so it is given by.
p = n* q ---------------------------------(2)

where,
n = no. of charge carrier (say electron in our case)
           q = charge carried by charge carrier.

C] Drift Velocity is given by
Vd = u*E  -------------------------------(3)
where,
u = Mobility
E =  Electric field.

So J becomes,
J = n*q*u*E  -------------------(4)

D] Ohm's law according to classical electromagnetic theory is given by,
J = k*E -------------------------------(5)
where,
k = conductivity
E = Electric field.

 Equating 4 and 5 we have

k = n* q* u

for above question
  n = Nd as it is n-type semiconductor.
q = charge on electron = 1.6E-16
u = 1350
 substituting in equation (6) we get,

k = 9.2592 E+14
so answer is B

Ans. A

JFET is three terminal  amplifier(used to increase amplitude of signal). three terminals are Drain( to take out current), Source(Source from where current is given out ). Operation is quite simple of the JFET. When no voltage is applied to gate terminal and suppose we apply + voltage Between Drain and source, electron  flows  from drain to source in the channel (region which connects drain and source shown by white color area) which creates current. now if apply negative voltage at gate terminal it will produce depletion region between gate and channel(shown by red color) as we go on increasing the negative drain voltage it continuously increases width of depletion region at some point say pinch off point depletion regions are so closed that further increase in negative voltage has no effect on depletion region.at this point JFET possesses maximum current Idss which remain almost constant.

Region1 -->   Ohmic region  -->   Drain current increase with increase in Drain voltage at constant                                                              gate  voltage(1 st curve)
Region 2 -->  Saturation  -->        Drain current remain constant (Pinch off region)

BASIC ON CONTROL SYSTEM

Control systems in general are classified as open loop and closed loop.

Open loop control system is those system which gives output dependent on present input, it does not interpret past inputs. good example is Electric Fan.

Electric Fan:

Suppose we are sitting in room in summer season and unfortunately speed of fan is slow enough to get lot of sweat, now you pray to god that please increase speed of fan but speed will remain slow until you go and increase it. now to increase speed of fan you required to change input voltage such system is good example for Open loop system.

Closed loop systems are probably an intelligent systems which can be controlled from present conditions also from past conditions.Good example is Refrigerator,Air conditioner.

Suppose you are sitting in room in summer season unlike fans AC sense temperature and respectively adjust its temperature (If environment conditions are hot then AC will try to keep room at lower temperature finally ! God had listen us and reduce temperature as needed in Summer season.)


Basic aspect of Control system:

• To control response of system.(Transient analysis)
• To obtain stable system.(Stability analysis)
• To obtain Response of system.(Root locus, Bode plot, Nyquist plot)
• To compensate various factor that affect response of system.(Compensation)

All this are central aspect of control system design. so  i will address each on in clear and lucid way.

Ans. A
Question ask about stability which is obtained from poles of closed loop transfer function( poles are denominator of the transfer function)