Basic Electrical/Resistance/Level-1/Paper-02

Resistance is defined as the property of a substance due to which it opposes  the flow of electricity  through it.Unit ohm  Ω.

Laws of Resistance

(i) Resistance decreases with decrease in   its length, l.

(ii) Resistance decreases with increase in the cross-section A of the conductor.
     i.e. Thicker wire has   lower resistance.

(iii) Resistance depends on the nature of the material the conductor made of.

(iv) Resistance also depends on the temperature of the conductor.

 

          

where ρ is a constant depending on the nature of the material of the conductor and is known as                   its specific resistance or resistivity.Unit ohm-metre(Ω-m).

Conductance :

Conductance (G) is reciprocal of resistance.Unit  siemens (S).
 Earlier, this unit was called mho.

          

 Conductivity :

σ is called the conductivity or specific conductance of a conductor.

It is seen from the above equation that the conductivity of a material is given by

Hence, the unit of conductivity is siemens/metre (S/m).


Effect of Temperature on Resistance

• Insulators (such as paper, rubber, glass, mica etc.) are said to possess a negative temperature-coefficient of resistance 
• Semiconductors have a positive temperature co-efficient of resistance.
• Metals have a positive temperature co-efficient of resistance.
•  The effect of rise in temperature is to decrease the resistance of electrolytes,and partial conductors such as carbon.

Q1. A given wire is stretched to double its length. How much its resistance change ?

(1) resistance is same

(2) resistance becomes four times

(3) resistance becomes two times

(4) resistance becomes half times

Ans: 2
Hint:

After stretching the resistance changes but resistivity remains the same.
As volume of wire is constant so area and length are inversely proportional.

So if the length is doubled by stretching , area of cross section becomes halved.

After stretching wire length is doubled.New length is 2l .

.
Q2. Two cylindrical resistors, R1 and R2, are made of identical material. R2 has twice the length of R1 but half the radius of R1.

Solution:
The area of a circle is equal to the square of its radius times Pi.Relationship between the cross section  area of half the radius of R1 with R2.

Resistance is inversely proportional to the area of cross section.

EL Engg/Semiconductor Engineering/Level-1//Paper-01

1. In intrinsic semiconductors, number of electrons __________ number of holes. 

(a) Equal (b) Greater than (c) Less than (d) Can not define

Ans: (c) Less than

2. Fermi energy level for intrinsic semiconductors lies

(a) At middle of the band gap (b) Close to conduction band
(c) Close to valence band (d) None

Ans:(c) Close to valence band

3. Flow of electrons is affected by the following


(a) Thermal vibrations (b) Impurity atoms (c) Crystal defects (d) all

Ans: (d) all

4. Fermi level for extrinsic semiconductor depends on 

(a) Donor element (b) Impurity concentration (c) Temperature (d) All

Ans:(d) All

5. Fermi energy level for n-type extrinsic semiconductors lies 

(a) At middle of the band gap (b) Close to conduction band 

(c) Close to valence band (d) None

Ans: (b) Close to conduction band 

_______________________________SOLUTION___________________________________

5. Ans: (b) Close to conduction band.
The Fermi level lies in the middle of the forbidden gap.
Fermi level lies near valence band in P type and near conduction band in N type

General Science/Level-1/Set-1/Paper-01

1. Radiations infra-red region may be detected with the help of
a)barometer
b)bolometer
c)spectrometer
d)sonometer
Ans:B bolometer

2. Simple astronomical telescope consist of two
A)convex lenses
B)concave lenses
C)one convex lens and other concave lens
D)Plano convex lenses
Ans: a convex lensses

3.A yellow object when seen through a red glass appears as
A)yellow
B)red
C)white
D)black
Ans.d black

4.X rays are emitted when
A)high energy electrons hit a substance of low molecular weight
B)high energy electrons hit a substance of high molecular weight
C)low energy electons hit any substance
D)low energy electons hit a substance of high molecular weight
Ans:b

5. Which of the following can be deflected by a magnet?
A)radio waves
B)X rays
C)beta rays
D)ultra violet rays
Ans.B beta rays

EL/Power Amplifiers/Level-1/Set -1/Paper-01

1.Which of the push-pull amplifiers is presently the most popular form of the class B power amplifier?

A) Quasi-complementary

B)Transformer-coupled

C)Complementary-symmetry

D)None of the above

 Ans:A) Quasi-complementary

2. In a class C amplifier 

A) Efficiency and distortion both are maximum 

B) Efficiency and distortion both are minimum. 

C) Efficiency maximum but distortion minimum. 

D) Efficiency minimum but distortion maximum

3. High power efficiency of the push-pull amplifier is due to the fact 

A) Each transistor conducts on different cycles of the input. 

B) Transistors are placed in CE configuration. 

C) There is almost no quiescent collector current 

D) Low forward biasing voltage is required.

4. Which amplifier is commonly used as a frequency multiplier?

A) class A

B) class B

C) class C

D) all of the above

Ans:D) all of the above

Basic Electrical/Electric Current/Level-0/Paper-01

Q1. A perfect conductor has

(a) Zero conductivity

(b) unity conductivity

(c) infinite conductivity

(d) none of  the above

Ans:c

Q2. The conductivity of a conductor can be increasingly

(a) decreasing its temperature

(b) increasing its temperature

(c) decreasing its vibration

(d) increasing its vibration

Ans: a

Q3. Which of the following  are no-conductors of electricity ?

(a) Non-metal solids except carbon

(b) Air and most other gases

(c) Pure water and liquids

(d) All of the above

Ans:d

Q4. Unit of electrical conductivity

(a) mho/metre (b) mho/sq.m  (c)ohm/metre (d)ohm/sq.m

Ans:a

Q5.Resistance of a material always decreases I

(a) temperature of material is decreased

(b)temperature of material is increased

(c)number of free electrons available become more

(d)none of the above is correct

Ans:c

CS/Computer Generation/Level -0/Paper-01

Q1. Microprogramming is a designing of

(a)ALU (b)CPU (c)ROM  (d)Control Unit

Ans: d

Q2.Which of the following code used in present day computing was developed by IBM Corporation?

A) ASCII

B) Hollerith Code

C) Baudot Code

D) EBCDIC Code

Ans:d

Q.3 What difference does the 5th generation computer have from other generation computers?

(a) Technological advancement

(b) Scientific code

(c) Object Oriented Programming     

(d) All of the above

(e) None of the above

Ans:d

Q4. Which of the following memory is responsible for co-ordinating various operations using timing signals?

(a) ALU    (b) Control Unit (c) Memory Unit (d) I/O Unit

Ans:b

Q5. Keyboard Converts typed in character to___________code

(a)EBCIDIC  (b) ASCII (c) None of these

Ans:b

Classes of amplifier operations: Class A B C

Q 1. Which class of amplifier has the lowest efficiency ?

   (a)Class A   (b)Class B   (c)Class C  (d)Class AB


Q2.A push pull amplifier is biased

(a) Class A    (b)Class C   (c) Class AB     (d)Class B


Q3 Maximum efficiency of a Class A amplifier is

 (a) 50%              (b)78.5 %       (c)80%   (d)100%


Q4 Which of the follwing typs of  amplifiers corresponds to a half wave rectifier ?

 (a)Class A   (b)Class B   (c)Class C    (d)class AB


Q5 Which type of power amplifier is biased for operation at less than 180º of the cycle?

(a)Class A   (b)Class B   (c)Class C    (d)class AB



_____________________________SOLUTIONS____________________________________
Q1.Ans: a

Q2. Ans: d,In Class B operatio, the linear operation of Class A can be obtained by using two matched transistors in push pull , each of them operating for half of the input signal period.
Q3. Ans b
Memorise the Hint:
ɳ CLASS Cab BA amplifier ==>i.e 100% ,50-78.5%,78.5%,50%  
Distortion proportional to Efficiency.
Conduction angle ===> Class C 90, class B 180,Class A 360

	class C	Class AB	Class B	Class A
Efficiency ɳ	100%	50% -78.5 %	78.5%	50%
Conduction angle	small (~90 Degree)	360 to 180 Degree	180 Degree	360 Degree
Bias	Revote	Forward	zero	Forward
Distortion	Extream	Moderate	High	Low

Q4. Ans b

Q5. Ans c