Guru Gobind Singh Indraprastha Vishwavidyalaya 2004 B.Tech ETES – 112 Subject : Electrical Science - Question Paper

First Term exam
Second Semester [B.Tech] February 2004

Paper Code : ETES – 112 Subject : Electrical Science

Time : 1:30 Hours
Maximum Marks : 30

Note : Attempt Q.1 and any two more ques..

Q1
( a )
describe temperature coefficient of resistance and write name of 2 materials having negative temperature coefficient of resistance.
1

( b )
Determine RAB of the infinite ladder network shown beneath if R1=2 ohm and R2=3 ohm.

R1 R1 R1
A----^v^v^----+----^v^v^----+----^v^v^----+ - - - - - - -
| | |
< < <
> > > ----infinity
< R2 < R2 < R2
> > >
| | |
B-------------+-------------+-------------+ - - - - - - - 2

( c )
In circuit shown beneath for R=20 ohm the current I is two A. obtain the current I when R=100 ohm.

+-------+ __ I +-------+
| N1 |-----(->)-----^v^v^v^-----+----->----| N2 |
+-------+ 4A R | +-------+
<
> 20 ohm
* __ <
(->) = current source |
^v^v^v^ = resistance |
|(Earth)| 1

( d )
Write the limitations of superposition theorem.
1

( e )
A current i=10+20 sin (wt) is flowing through 10 ohm resistance. compute the energy dissipated by the resistance.
1

( f )
describe power factor and write its significance in AC circuits.
1

( g )
In the circuit shown below, VAB = three V when R=infinite and current I is 3A when R=Zero. obtain current I if R=2 ohm.
2

( h )
Why a Wheatstone bridge cannot be used for precision measurement of low resistances?
1

Q2
( a )
Derive the equations for balance in case of Maxwell's inductance-capacitance bridge. Draw the phasor diagram for balance conditions.
4

( b )
Determine the current flowing through six ohm resistance in circuit shown beneath using Thevenin's Theorem.
6

Q3
( a )
compute the avg. and R.M.S. Value of a clipped full rectified sine wave, shown below:

^
|
|
Em + ... ...
| . . . .
| ._______. ._______.
Em/1.414 + / \ / \
| / \ / \
| / \ / \
| / \ / \
|/ \/ \
----+-----+--------+----+----+-------+-----+-------->
0| pi/4 3pi/4 pi 5pi/4 7pi/4 pi
| 3

( b )
A coil having a resistance of 50 ohms and an inductance of 0.2 H is connected in series with a capacitor. The current is maximum when frequency is 50 Hz. compute the capacitance of the condenser to be connected in parallel with the above combination so that the total current drawn from the mains is minimum when frequency is 100 Hz. Draw the phasor diagram, representing all the currents at 100Hz. Take supply voltage as reference.
5

( c )
Derive an expression for dynamic impedance in parallel resonance.
2

Q4
( a )
In the circuit shown in figure, the identical current flows through every element. If Vx=1V and Vr=9V, calculate :

the power absorbed by element A

power supplied by every of the 2 sources

Does the total power supplied = total power absorbed? Is your finding reasonable? Why or Why not?

+ +------+ -
+------------| A |----------+
| +------+ |
| Vr |
| |
Vx --- + / \
- - PD=8 V < | > Current Source I= 5*Vx
| \v/
| |
| |
+------------------------------+ 3

( b )
In the circuit shown beneath V1=40V when R=10 ohms. obtain V2 when R is zero.

10 ohm V1 R V2 10 ohm
+---^v^v^v^---+---^v^v^v^---+---^v^v^v^---+----+
| | | | |
60V --- + < < < |
- - > 20 ohm > 20 ohm > (^) Current source 5A
| < < 20 ohm < |
| | | | |
+-------------+-------------+-------------+----+ 3

( c )
A filament of 60 W, 220V, electrical bulb has 2000o C working temperature. compute current flowing through the filament at:

Working Temperature

Room Temperature (30o)

presume temperature coefficient of resistance 0.0045 peroC at room temperature.
4

Earning:   Approval pending.