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ECE - 2006

1. A negative resistance R is connected to a passive network N having driving point impedance (s) as shown below. For

(s) to be positive real,

(A) |R | Re (j ) (B) |R | | (j )|

(C) |R | m (j ) (D) |R | (j ) ECE - 2007

2. For the circuit shown in the figure, the Thevenin voltage and resistance looking into X –Y are

(A) 4/3 V 2Ω (B) 4V 2/3 Ω

(C) 4/3 V 2/3Ω (D) 4V 2Ω ECE - 2009

3. In the circuit shown, what value of RL

maximizes the power delivered to RL?

(A) 2.4 Ω (B) 8 3⁄ Ω

(C) 4 Ω (D) 6 Ω

4. In the interconnection of ideal source shown in the figure, it is known that the 60V source is absorbing power.

Which of the following can be the value of the current source I?

(A) 10 A (B) 13A

(C) 15A (D) 18A

ECE - 2010

5. In the circuit shown, the power supplied by the voltage source is

(A) 0 W (B) 5 W

(C) 10 W (D) 100 W ECE - 2011

6. In the circuit shown below, the value of R such that the power transferred to R is maximum is

(A) 5Ω (B) 10Ω

(C) 15Ω (D) 20Ω

10 Ω 10 Ω

10 Ω R

5V 2V 1

2 1

10V

12 A + 20 V

60 V

I

4Ω 4Ω 4Ω

100V R

V

V

V

2Ω 2

1Ω i 2i 1Ω Z2(s)

Rneg

N

Z1(s)

7. In the circuit shown below, the current I is equal to

(A) 1.4 0 A (B) 2.0 0 A

(C) 2.8 0 A (D) 3.2 0 A

8. In the circuit shown below, the Norton equivalent current in amperes with respect to the terminals P and Q is

(A) 6.4 – j4.8 (B) 6.56 – j7.87

(C) 10 + j0 (D) 16 + j0

ECE/IN - 2012

9. The average power delivered to an impedance (4 j3) by a current

5cos (100t+100) A is (A) 44.2 W

(B) 50 W

(C) 62.5 W (D) 125 W ECE/EE/IN - 2012

10. The impedance looking into nodes 1 and 2 in the given circuit is

(A) 50  (B) 100 

(C) 5 k

(D) 10.1 k

11. If VA VB =6 V, then VC VD is

(A) 5 V (B) 2 V

(C) 3 V (D) 6 V ECE/EE/IN - 2013

12. Consider a delta connection of resistors and its equivalent star connection as shown. If all elements of the delta connection are scaled by a factor k, k>0, the elements of the corresponding star equivalent will be scaled by a factor of

(A) k (B) k

(C) 1/k (D) √k

13. Three capacitors C1, C2 and C3 whose values are 10μF 5μF and 2μF +respectively, have breakdown voltages of 10V, 5V and 2V respectively. For the interconnection shown below , the maximum safe voltage in Volts that can be applied across the combination, and the corresponding total charge in μC stored in the effective capacitance across the terminals are respectively,

(A) 2.8 and 36 (B) 7 and 119

(C) 2.8 and 32 (D) 7 and 80 C2 C3

C1

Ra

Rb Rc

RA

RB

RC

R 10V R

R

R R

V

R

R V

V

V 2

5V R

2 1

99i

1kΩ

100Ω 9kΩ

i

16 0 25Ω

15Ω

j50Ω P

Q j30Ω

~

j4Ω

14 0 V

j4Ω

ECE - 2014

14. For maximum power transfer between two cascaded sections of an electrical network, the relationship between the output impedance of the first section to the input impedance of the second section is

(A) (B)

(C) (D) 15. Consider the configuration shown in the

figure which is a portion of a larger electrical network

For R 1Ω and currents i =2 i 1 i 4 which one of the following is TRUE?

(A) i 5 (B) i 4

(C) Data is sufficient to conclude that the supposed currents are impossible (D) Data is insufficient to identify the

currents i i and i

16. A Y-network has resistances of 10Ω each in two of its arms, while the third arm has a resistance of 11 Ω. In the equivalent -network, the lowest value (in Ω.) among the three resistances is ________

17. Norton’s theorem states that a complex network connected to a load can be replaced with an equivalent impedance (A) in series with a current source (B) in parallel with a voltage source (C) in series with a voltage source (D) in parallel with a current source

18. In the figure shown, the value of the current I (in Amperes) is______.

19. In the circuit shown in the figure, the value of node voltage V is

(A) 22 + j 2 V (B) 2 + j 22 V

(C) 22 – j 2 V (D) 2 – j 22 V 20. The circuit shown in the figure, the

angular frequency (in rad/s) at which the Norton equivalent impedance as seen from terminals b-b′ is purely resistive is_____________.

21. For the Y-network shown in the figure, the value of R (in Ω) in the equivalent

∆-network is ____.

R

7.5Ω

~

b

b′

1F

0.5

10 cos t (volts)

j6Ω V V

4 0

10 0

j3Ω

10Ω 5Ω

5V 1

R R R

i i

i

i i

i

22. The magnitude of current (in mA) through the resistor R in the figure shown is__________

23. The equivalent resistance in the infinite ladder network shown in the figure, is R .

The value of R /R is________

24. The circuit shown in the figure represents a

(A) voltage controlled voltage source (B) voltage controlled current source (C) current controlled current source (D) current controlled voltage source EE - 2006

1. The three limbed non ideal core shown in the figure has three winding with nominal inductances L each when measured individually with a signal phase AC source. The inductance of the winding as connected will be

(A) Very low (B) L/3

(C) 3L

(D) Very high EE - 2007

2. A 3V dc supply with an internal resistance of 2Ω supplies a passive non-linear resistance characterized by the relation VNL = . The power dissipated in the non-linear resistance is

(A) 1.0 W (B) 1.5 W

(C) 2.5 W (D) 3.0 W EE - 2008

3. In the circuit shown in the figure, the value of the current i will be given by

(A) 0.31 A (B) 1.25 A

(C) 1.75 A (D) 2.5 A

4. Assuming ideal elements in the circuit shown below, the voltage Vab will be

(A) – 3 V (B) 0 V

(C) 3 V (D) 5 V EE - 2009

Statements for Linked Answer Questions 5

& 6:

2kΩ

5V

3VAB

2kΩ +

B A

+ 1kΩ

5V

b 1A

Vab

i a

+

+

i

5V

4V

a b

V +

R

R

2R R R R

R R

R R R

R 2m 4kΩ 1kΩ

2kΩ R

10 m R

R 3kΩ

5. For the circuit given above, the Thevenin’s resistance across the terminals A and B is

(A) 0.5kΩ (B) 0.2kΩ

(C) 1kΩ (D) 0.11kΩ

6. For the circuit given above, the Thevenin’s voltage across the terminals and B is

(A) 1.25V (B) 0.25V

(C) 1V (D) 0.5V

7. How many 200W/220V incandescent lamps connected in series would consume the same total power as a single 100W/220V incandescent lamp?

(A) not possible (B) 4

(C) 3 (D) 2

8. For the circuit shown, find out the current flowing through the 2Ω resistance. Also identify the changes to be made to double the current through the 2Ω resistance.

(A) (5A; Put Vs=20V) (B) (2A; Put Vs =8V) (C) (5A; Put Is = 10A) (D) (7A; Put Is= 12A)

9. The current through the 2 kΩ resistance in the circuit shown is

(A) 0mA (B) 1mA

(C) 2mA (D) 6mA

EE - 2010

10. If the 12 Ω resistor draws a current of 1A as shown in the figure, the value of resistance R is

(A) 4Ω (B) 6Ω

(C) 8Ω (D) 18Ω

11. As shown in the figure, a 1Ω resistance is connected across a source that has a load line v + i = 100. The current through the resistance is

(A) 25A (B) 50A

(C) 100A (D) 200A EE - 2011

12. In the circuit given below, the value of R required for the transfer of maximum power to the load having a resistance of 3Ω is

(A) Zero (B) 6Ω

(C) 3Ω (D) Inifnity EC/EE/IN - 2012

13. Assuming both the voltage sources are in phase the value of R for which maximum power is transferred from circuit A to circuit B is

10 V 6Ω

3Ω oad R

Source

1Ω i

V

6V R

1Ω 2 1 12Ω

6V 1kΩ 1kΩ

1kΩ 1kΩ

2kΩ C

V 4V Is = 5A 2Ω

(A) 0.8 Ω (B) 1.4 Ω

(C) 2 Ω (D) 2.8 Ω EC/IN/EE - 2013

14. The following arrangement consists of an ideal transformer and an attenuator which attenuates by a factor of 0.8. An ac voltage V 100V is applied across WX to get an open circuit voltage V across YZ. Next , an ac voltage

V = 100V is applied across YZ to get an open circuit voltage V across WX.

Then,V /V V /V are respectively.

(A) 125/100 and 80/100 (B) 100/100 and 80/100 (C) 100/100 and 100/100 (D) 80/100 and 80/100 EE - 2014

15. The three circuit elements shown in the figure are part of an electric circuit. The total power absorbed by the three circuit elements in watts is ___________

16. In the figure, the value of resistor R is (25 + I/2) ohms, where I is the current in amperes. The current I is______

17. Two identical coupled inductors are connected in series. The measured inductances for the two possible series connections are 380 μH and 240 μH. Their mutual inductance in μH is_______

18. The total power dissipated in the circuit, shown in the figure, is 1 kW.

The voltmeter, across the load, reads 200 V. The value of is__________

19. The line A to neutral voltage is 10 15° V for a balanced three phase star-connected load with phase sequence ABC. The voltage of line B with respect to line C is given by

(A) 10√3 105 V (B) 10 105 V

(C) 10√3 75 V (D) 10√3 90 V 20. The Norton’s equivalent source in

amperes as seen into the terminals X and Y is _______

5V

2.5V

2.5Ω

~

V 200V oad

R

2 10

ac source

R 300V

8 10

2

100V 80V

15V

Y

Z W

X

1:1.25

~

j1Ω

~

3V

R

Circuit Circuit

10V

21. The power delivered by the current source, in the figure, is_____________

22. An incandescent lamp is marked 40 W, 240V. If resistance at room temperature (26°C) is 120 Ω, and temperature

coefficient of resistance is 4.5 10 /°C, then its ‘ON’ state filament temperature in

°C is approximately___________

IN - 2006

1. The root – mean – square value of a voltage waveform consisting of a superimposition of 2V dc and a 4V peak – to – peak square wave is

(A) 2 V (B) √6 V

(C) √8 V (D) √12 V IN - 2008

2. The power supplied by the dc voltage source in the circuit shown below is

(A) 0W (B) 1.0W

(C) 2.5W (D) 3.0W

3. Which one of the following equations is valid for the circuit shown below?

(A) 0 (B) 0 (C) 0 (D) 0

4. The current I supplied by the dc voltage source in the circuit shown below is

(A) 0A (B) 0.5A

(C) 1A (D) 2A

5. In the circuit shown below the maximum power that can be transferred to the load

is

(A) 250 W (B) 500 W

(C) 1000 W (D) 2000 W 10Ω

10 m

i(t)10√2sin

(10

00t)

1V 1A

1Ω I

1Ω

I7

5V

I4

1Ω 1Ω

1Ω 1Ω

1Ω

1Ω I5

I2

I1 I3

I6

+

1Ω 3Ω

6Ω 3Ω

3V

2 1V

1V

IN - 2009

6. The source network S is connected to the load network L as shown by dashed lines.

The power transferred from S to L would be maximum when RL is

(A) 0Ω (B) 0.6 Ω

(C) 0.8 Ω (D) 2Ω IN - 2010

7. A 100 Ω , 1W resistor and a 800 Ω , 2W resistor are connected in series. The maximum dc voltage that can be applied continuously to the series circuit without exceeding the power limit of any of the resistors is

(A) 90V (B) 50 V

(C) 45 V (D) 40V IN - 2011

8. The current I shown in the circuit given below is equal to

(A) 3 A (B) 3.67 A

(C) 6 A (D) 9 A

IN - 2014

9. The circuit shown in the figure contains a dependent current source between A and terminals. The Thevenin’s equivalent resistance in kΩ between the terminals C and D is ___________.

10 V

V

5kΩ 5kΩ

10 V

C

10Ω

10Ω

10 V 10 10Ω

+

2Ω RL

3V

Load Network L Source Network S

10 V

+

Answer Keys and Explanations

ECE

1. [Ans. A]

(s) = (S) R

(s) (R R ( (s))

m( (s)) R 0 For (s)to be +ve & real,

Re ( (s)) R |Re( (s))| |R | 2. [Ans. D]

For V

Apply nodal analysis, V

2 2 V V 2i

1 0 V i V

2 2 2V 2i 0 V 2 2 V V 4V

Similarly, 2 V 4V R

V

3. [Ans. C]

For maximum power transfer, R R

V 100V

100 8

(100 V) 4 Also V 50V

12.5 12.5 25 R V

4Ω R 4Ω

4. [Ans. A]

In the given circuit, the current through the branch of 60 V source is (12 –I) as shown in Fig. The source of 60 V absorbs power, only if

P =(12 – I)60 is +ve. i.e., I<12.

The value of the current source, I can only be 10A given in option (a), as the currents given in other options are more than 12 A.

5. [Ans. A]

The current through all the branches are marked as shown in Fig. 1.

Apply KVL to outer loop 2( 3) 2( 2) 10 4 10 10

0

Power supplied by 10 V 10 0 0 6. [Ans. C]

For Maximum power transfer to RL R 15

10

10 10

Fig. 2

2 1

10V

( 3)

( 2)

( 2)

3 3

Fig .1 I

60V 12 A 20 V

12 A

I 12 A

(12 – I)A +

4Ω 4Ω 4Ω

100V

V

V

x

y 2

i

2i

V

R R

R Thevenin’s resistance seen across the terminals of R into the rest of the network. The relevant circuit is shown in Fig.2, where the independent current source is open circuited and the voltage sources are short circuited.

R 10 (10 10) R R 15Ω

7. [Ans. B]

To find the current I in the given circuit in Fig. (1), the delta network with 6Ω each is converted to a star as shown in Fig. (2)

Then the given circuit reduces to Fig. (3), (4) and (5)

Where (2 j4)||(2 j4) 5Ω and 14 0

7 2 0

8. [Ans. A]

The Norton equivalent current is 16 0 25

(40 30) 8 tan (3

4) 8 36.86 (6.4 j4.8)

9. [Ans. B]

The load consists of a resistance and a capacitance of this, only R is passive and consumes power

So P = R

= () 4 50

*Note rms value of cos t

+.

10. [Ans. A]

After connecting a voltage source of V V V

(10k)( i ) 100( 99i i ) 10000i 100( 100 i )

100 10000i 20000i 100

i ( 100

20000) [ 200] V 100 99i i

100 [ 100 ( 200)]

50 R V 50

50Ω

99i V ( 99i )

V 100Ω

V 10kΩ

i

99i

1kΩ

100Ω 9kΩ

i

2 Ω 14 0

14 0

Fig. 4

2 Ω 2 Ω 2 Ω

j4Ω j4Ω

14 0

Fig. 3

~

14 0 V

j4 Ω

6 Ω 6 Ω

j4 Ω

Fig. 1 6 Ω

2 Ω 2 Ω

2 Ω

6 Ω 6 Ω

Fig. 2

11. [Ans. A]

For safe warping voltage across should not increased from 2V

V C V

For maximum power transfer

Load impedance = complex conjugate of

17. [Ans. D]

Norton’s theorem: Here for a complex network, after isolating the element, we short circuit the two ends and find the current . is the current of the independent current source with the equivalent resistance in parallel

18. [Ans. *] Range 0.49 to 0.51 Apply superposition theorem For voltage

5

20 0.25 mp For current

1 5

20 0.25 mp

(0.25 0.25) 0.50 mp 19. [Ans. D]

Using super node concept, we can treat nodes 1 and 2 to gather as a super node as shown in the figure by the dotted lines

Applying KCL to the super node we have 4 0 V

3j V

6 V

6j 0 . From super node we get

V V 10 0 . Solving and for V we get V 2 22j V

20. [Ans. *] Range 1.9 to 2.1

The Norton’s equivalent circuit is

In doiman

(1||0.5j ) 1 j 0.5j

1 0.5j j 0.5j (1 0.5j )

1 0.25

j

0.5j (1 0.5j ) j(1 0.25 ) (1 0.25 )

Equating the imaginary part to zero, we get

0.5 1 0.25 0 0.25 1

2rad/sec

Voltage source shorted

0.5

1F

6jΩ

3jΩ 10 0 V

V2 V1

4 0

10Ω

1

10Ω

5V

R

21. [Ans. *] Range 9 to 11

R 5 3 5 7.5 3 7.5 7.5

7.5 2 5 3

7.5 10

22. [Ans. *] Range 2.79 to 2.81

By source transformation theorem

by KV 20 10k 8 0 28

10k 2.8 m 23. [Ans. *] Range 2.60 to 2.64

We know that in a infinite ladder network if all resistance are comprises of same value R then the equivalent resistance is

( √ )

. Then the above given network can be redrawn as R series with R equivalent as follows

R R 1.618R 2.618R

R

R 2.618 24. [Ans. C ]

In the above circuit in the output side there is a dependent current source which is controlled by the input current and hence it is a current control current source.

EE

1. [Ans. A]

The inductance of all three coils are ‘ ’ and they are connected to same line carrying the same current and set up the flux in the same direction

All these fluxes linked with each other and they will balance each other. So net flux will reduce drastically. Thus net L will be very low

2. [Ans. A]

3 2 1

Power delivered by source = 3×1=3W.

3V I V

+

2 2

i i R

R (1 √5)R 2 R

R

2k 1k 4k

3k

8V 20V

R

7.5Ω

Power dissipated by 2Ω resistor 2 2 .

Power dissipated in non-linear element

= 3-2=1W 3. [Ans. B]

V 5 1

2 2.5V

Also, 4 V 4i 4(V V ) 4i . (1) Also, V 4V V V

V V

2 1.25 V

4(2.5 1.25) 4i (From (1)) i 1.25

4. [Ans. A]

V 2i 5 2 5 3V 5. [Ans. B]

Thevenin’s resistance is calculated using the circuit shown in fig. (1) and (2), where independent voltage source is short circuited

Write the loop equation :

V 3 V ( V 10 )10 10 V

5V 10 R V 10

5 Ω 0.2kΩ

6. [Ans. D]

To calculate thevenin’s voltage terminals A-B are kept open.

Applying source transformation into correct source

Applying source transformation current source is transformed into voltage source.

Applying KVL, {I is assumed to be in mA}

5

2 1k 3V 1k 0 5

2 2k 3V 0 (1) V

1k (2)

Put the value of in quation (1) 5

2 2V 3V 0 V 0.5V

7. [Ans. D]

For a lamp, P KV

For 200 220V⁄ lamp, K 200⁄220 Consider n lamps connected in series, Total power consumed n K 110 100 n 110 100 n 2

V

3V

1kΩ

1kΩ

5 2V

C 2kΩ 2kΩ

C

C

1kΩ V 3V

2kΩ

1kΩ 2kΩ

5V

C

2kΩ

2kΩ 1kΩ V

3 V

I

A

B Fig. 1

Fig. 1

1kΩ 1kΩ

3 V

V

A

B V 10

I

Fig. 2

( V 10)

8. [Ans. B]

The relevant circuit is shown in fig.

As the voltage across 2Ω 4V 4

2 2

In order to double the current through 2Ω resistance, V is to be doubled (Put V 8V) ]

Note that the 5 A source has no effect on the answer. However it gives 3A current through the voltage source as shown in fig.

9. [Ans. A]

As the ABCD bridge is balanced, 0 10. [Ans. B]

Current through R =1A By KVL, 1.R +6=12

 R = 6  11. [Ans. B]

V i 100 and V i .1(by ohm’s law) 2i 100  i 50

12. [Ans. B]

To calculated voltage source is short circuited

R 6||R 6R 6 R

According to maximum power transfer theorem

R R 3 6R 6 R R 6Ω

13. [Ans. A]

For maximum power transfer

Source impedance = Load impedance z R

10

4 2.5 So in our circuit

pply KV in loop 5 2.5R 3 0 [R 2

2.5 0.8Ω]

14. [Ans. B]

V 100 V turns ratio V 125

V 0.8 V 100V when V 100V

100 V 125 V

X W

Y

Z V

1:1.25

~

5V

~

10V

2.5 R

3V

~

5V

5V

10V

~

j1Ω

~

3V

R

Circuit Circuit 10V

R

6

R

V 4V 5 2Ω

3

Fig.

Thevenin’s circuit seen by 2 2′ will be as follow

V 100V

nd R 0.2||0.8 negligible V 100V

V V turns ratio 100V 1

1.25 80V 15. [Ans. 330]

Power absorbed by battery 100V = 100 10 1000

Power supplied by battery 80V 80 8 640

Current through 15V battery 10 8

2

Power supplied by battery 15V 15 2 30 Total power absorbed

1000 640 30 330 att

16. [Ans. 10]

300 (25 2) 600 (50 ) 10 17. [Ans. 35]

Total flux linkage = i

total

380μm

240μm 4 140μm

35μ

18. [Ans. *] Range 17.3 to 17.4 200 (10)√ R

Power dissipated (2) (1) R 10 4 10R 1000

R 996 10 400 R

400 99.6 17.33Ω 19. [Ans. C]

V lags voltage A by 90 V √3 10 90 Angle 90 with respect to A Hence

V √3 10 ( 90 15) 10√3 75

20. [Ans. 2]

Terminal x – y shorted Applying superposition i due to 5V

(5) (5 )

5 7.5 5 3

20 5 7.5

5 10 0.5 i due to 2.5V

5V

2.5V

2.5Ω

i 120 120

C

120

2

0.8 100V

V

2′

2.5 (2.5 2.5)

1 2 0.5

Total i 0.5 0.5 1 (NOTE: Option not matching with IIT website)

21. [Ans. 3]

R is resistance of room temperature (240)

For square wave voltage with peak – to – peak value of 4 V or amplitude = 2V, M.S.V = 4 + 4 = 8

R. . S. V √8 V

2. [Ans. D]

The given circuit in Fig. 1 is simplified as shown in Fig. 2 and Fig.3

Apply KCL at nodes,

At node, P

The circuit is shown in Fig.

Voltage across 1 =1V 1 = 1A

I+1= I1, or I+1=1 , 0 5. [Ans. B]

The circuit is shown in Fig. 1

i(t) 10√2 Sin (1000 t) 10 /

Phasor of i(t) 10√2

R j 10 j10 10 10 10 j 10

The Thevenin equivalent circuit is shown in Fig. 2

10 j 10 V⃗⃗⃗⃗ 10√2

10√2(10 j 10) 200 e

For maximum power transfer to load, 10 j 10 R 10Ω

⃗⃗⃗ V⃗⃗⃗⃗

20 10 e i (t) 10 sin( 45 )

10 (rms) 10

√2 Power transferred to load, P (rms) R 100

2 10 500 6. [Ans. C]

The circuit is shown in Fig.

7

2 R

Power supplied by the 10V source, P

Power dissipated in 2 resistance, P 2 98

(2 R )

Power transferred to the network, P(R ) P P

( )

P would be maximum, if 0 70

(2 R ) 98 2

(2 R ) 0 196

2 R 70 2 R 196 70

98 35

R 98

35 2 28

35 0.8  7. [Ans. C]

Resistor 1 : 100 Ω 1 Resistor 2 : 800 Ω, 2 W

Maximum current that resistor can withstand

√ 1 100

1 10 Similarly,

√ 2 800

1 20

If these two resistors are connected in series.

Then maximum value of

100Ω 800Ω

V I

+

2Ω RL

3V

Load Network L Source Network S

10 V I

+

+

V⃗⃗

Fig. 2 10Ω

10 m

10Ω i(t)

V (100 800) 1

20(900) 45Volts 8. [Ans. A]

The given circuit is Fig. 1

Convert the (10 V, 10 Ω) voltage source across A, B to the left into a current source, (1 A, 10 Ω). The resultant circuit is shown in Fig. 2

The circuit is further simplified as shown in Fig. 3 and 4

9 5

15 3

9. [Ans. 20]

For R calculation Independent voltage source should be short circuited So

So *R + Apply KCL at Node A 10 V 1 V

5k 10 V 5K 1 V .5 V

2V 1.5 V 0.75V So 1 V

5k

1 0.75 5k 0.25

5k 5 10 0.05m

[R 1

0.05m 20kΩ]

10 V

R 5k

5K

so V 1 C

1V( ssume) 10 V

5kΩ 5kΩ

10 V

C

V

5Ω 10Ω

Fig. 4 9

5Ω 10 10Ω

Fig. 3 1

10Ω 10 10Ω

Fig. 2 10Ω

1 10Ω

10Ω

10 V 10 10Ω

Fig. 1

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