Explore topic-wise InterviewSolutions in .

Right answer is (B) Voltage source in SERIES with a resistor

For explanation I WOULD say: A CURRENT source connected in parallel can be converted to a voltage source connected in series USING the relation obtained from Ohm’s law, that is V=IR. This equation shows that a current source connected in parallel has the same impact as a voltage source connected in series.

Right choice is (c) 6.67V

The explanation is: 4 ohm is removed and then V ACROSS 2 ohm is calculated by voltage divider 2*10/(2+1) = 6.67V. Voltage between A and B i.e. Vth is equal to voltage across 4 ohm RESISTANCE SINCE no current flow through 3 ohm resistance. So, Vth = 6.67V.

Correct ANSWER is (b) 4.57V

To ELABORATE: The TWO nodal equations are:

(VA-10)/3+VA/2=0

(VB-20)/4+VB/3=0

On SOLVING the two equations, we get VA=4V, VB=8.571V.

VAB = VA-VB = 4V – 8.571V = -4.57V.

Eth = 4.57V.

Right choice is (a) LINEAR SYSTEMS

Explanation: Superposition THEOREM is valid only for linear systems because the effect of a single source cannot be INDIVIDUALLY calculated in a non-linear system.

The correct ANSWER is (B) Value of load resistance

To explain I would SAY: The maximum power TRANSFERRED is equal to E^2/4*RL. So, we can say maximum power depends on load resistance.

Right choice is (a) 34 OHM, 18.67 ohm, 3.19 ohm

Explanation: Using the formula for delta to STAR CONVERSION:

Using the formula for delta to star conversion:

R1=1+2+1*2/(32/3)

R2=1+32/3+1*(32/3)/2

R3=2+32/3+2*(32/3)/1.

Right answer is (a) In series with the voltage source

To ELABORATE: The resistance is CONNECTED in series with the voltage source because we are TRANSFORMING a current source connected in PARALLEL to a RESISTOR to a voltage source connected in series with it.

The correct answer is (a) 0.72A

The best I can explain: Since the 5 ohm is the LOAD resistance, we SHORT it and find the resistance through the short.

If we apply SOURCE transformation between the 6 ohm resistor and the 1A source, we get a 6V source in series with a 6 ohm resistor. Now we have two meshes. Let us consider I1 flowing in the FIRST mesh and I2 flowing in the second mesh.

The mesh equations are:

9I1-6I2=4

-6I1+16I2=6

On solving these equations simultaneously, we get I2=0.72A, which is the short circuit current.

The correct option is (a) 0V

The best I can explain: DUE to 15 A current SOURCE, 10V and 16V sources get shorted and the 3A source acts as an open circuit. Since the 10V source is shorted, it acts as a low resistance path and current flows only WITHIN that loop and do not flow to the 20 ohm RESISTOR. HENCE the voltage is 0V.

Right ANSWER is (a) SHORTED

The explanation: In SUPERPOSITION theorem when we consider the effect of one VOLTAGE source, all the other voltage sources are shorted and current sources are opened.

The CORRECT OPTION is (a) 1.739 V

For EXPLANATION: 5-3I1+2I2=0, 9I2-2I1=0, -4I2+V=0

On SOLVING,V=1.739V.

Right CHOICE is (b) Nodal ANALYSIS

To explain: KCL employs nodal analysis to find the DIFFERENT node voltages by finding the value if a current in each branch.

Correct OPTION is (d) 2.38 ohm

For explanation: The 3 2ohm RESISTORS are connected in star, changing them to DELTA, we have R1=R2=R3= 2+2+2*2/2=6 ohm.

The 3 6ohm resistors are connected in parallel to the 10 ohm 5 ohm and 10ohm resistors respectively.

This network can be further reduced to a network consisting of a 3.75ohm and 2.73ohm resistor connected in series whose resultant is intern connected in parallel to the 3.75 ohm resistor.

Correct choice is (B) Current source in parallel with a resistor

To elaborate: A voltage source connected in SERIES can be converted to a current source connected in parallel using the RELATION OBTAINED from Ohm’s law, that is V=IR. This equation shows that a voltage source connected in series has the same impact as a current source connected in parallel.

Correct answer is (b) No

Easy explanation: The 15A current source has a lower resistance PATH associated with it and hence it KEEPS moving in that particular loop. It does not LEAVE that loop and enter the circuit, hence the circuit is not affected by it.

Correct option is (C) 12 ohm

For EXPLANATION: Shorting all voltage SOURCES and OPENING all current sources we have:

RN=(3||6)+10 = 12 ohm.

Right option is (c) Shorting all voltage sources and opening all CURRENT sources

For explanation I would say: Ideal current sources have infinite internal RESISTANCE HENCE BEHAVE like an open circuit whereas ideal voltage sources have zero internal resistances hence behave as a short circuit. So, to obtain Norton resistance, all voltage sources are shorted and all current sources are opened.

The correct answer is (a) Linear networks

To elaborate: THEVENIN’s THEOREM WORKS for only linear CIRCUIT elements and not non-linear ones such as BJT, semiconductors etc.

Correct OPTION is (c) 11.33V, 26.67V

Explanation: The NODAL EQUATIONS are:

2V1-V2=-4

-4V1+5V2=88

Solving these equations SIMULTANEOUSLY, we GET V1=11.33V and V2=26.67V.

The CORRECT option is (a) 7.67A, 10.67A, 2A

To explain: The two MESHES which contain the 3A current is a super mesh. The THREE mesh EQUATIONS THEREFORE are:

I3=2A

I2-I1=3

-2I1-I2=-26

Solving these equations simultaneously we get:

I1=7.67A, I2=10.67A and I3=2A.

Correct choice is (c) Ra+Rb+Ra*Rb/Rc

Best explanation: After converting to the DELTA, each delta connected RESISTANCE is equal to the sum of the two resistances it is connected to+product of the two resistances DIVIDED by the remaining resistance. HENCE, resistance between A and B = Ra+Rb+Ra*Rb/Rc.

The CORRECT answer is (b) Ra+Rc+Ra*Rc/Rb

To explain I would say: After converting to the delta, each delta connected RESISTANCE is equal to the SUM of the two resistances it is connected to+product of the two resistances divided by the remaining resistance. HENCE, resistance between A and C = Ra+Rc+Ra*Rc/Rb.

Right choice is (b) The EFFECT of only one SOURCE is considered

For EXPLANATION: When voltages are CONNECTED in PARALLEL, the effect of only one source is considered because the effect of the voltage remains the same when connected in parallel.

Right answer is (b) Opened

Explanation: In superposition theorem, WHETHER we CONSIDER the effect of a VOLTAGE or current source, current sources are ALWAYS opened and voltage sources are always shorted.

The correct ANSWER is (a) 1.75A, 1.25A

For explanation I WOULD say: In this circuit, we have a super mesh present.

Let I1 and I2 be the currents in loops in clockwise direction. The two mesh equations are:

I2-I1=3

-5I1-3I2=5

Solving these equations simultaneously, we get I1 = -1.75A and I2 = 1.25A.

Since no specific direction given so currents in loop 1 and loop 2 are 1.75A and 1.25A respectively.

Right choice is (a) 83.33V

The best explanation: Taking I1, I2 and I3 as the currents in the three meshes and taking I3=0 since it is the current ACROSS the 1 ohm resistor, the three mesh EQUATIONS are:

15I1-5I2=V1

-5I1+10I2=0

3I2=10

Solving these equations SIMULTANEOUSLY we get V1= 83.33V.

Right option is (a) MESH analysis

The EXPLANATION: KVL EMPLOYS mesh analysis to find the different mesh currents by finding the IR PRODUCTS in each mesh.

The correct answer is (a) 0A

The EXPLANATION is: If we move in the CLOCKWISE direction, we get the total VOLTAGE to be equal to: -10-20+30 = 0V. Since I=V/R = 0/4=0, I=0A.

The CORRECT option is (a) 4ohm, 3OHM, 2ohm

To ELABORATE: Using the FORMULA for the star to delta conversion:

R1=8/9+4/3+(8/9)*(4/3)/(2/3)

R2=8/9+2/3+(8/9)*(2/3)/(4/3)

R3=2/3+4/3+(2/3)*(4/3)/(8/9).

Right OPTION is (a) R1=Ra*Rb/(Ra+Rb+RC), R2=Rb*Rc/(Ra+Rb+Rc), R3=Rc*Ra/(Ra+Rb+Rc)

To explain I WOULD say: After CONVERTING to STAR, each star connected resistance is equal to the ratio of product of the resistances it is connected to and the total sum of the resistances. Hence R1=Ra*Rb/(Ra+Rb+Rc), R2=Rb*Rc/(Ra+Rb+Rc), R3=Rc*Ra/(Ra+Rb+Rc).

Correct choice is (c) 50V

The EXPLANATION is: USING ohm’s law, we can USE the relation: V=IR.

Thus V=10*5 = 50V.

The correct choice is (a) Thevenin’s theorem

To EXPLAIN: Thevenin’s theorem is also known as the dual of Norton’s theorem because in Norton’s theorem we FIND short CIRCUIT current which is the dual of OPEN circuit voltage-what we find in Thevenin’s theorem.

The correct ANSWER is (a) 1

Easy EXPLANATION: In the nodal analysis, one node is treated as the reference node and the voltage at that POINT is TAKEN as 0.

The correct option is (B) CURRENT

For explanation I would SAY: Mesh analysis USES Kirchhoff’s Voltage Law to find all the mesh currents. Hence it is a method used to determine current.

The correct CHOICE is (B) 0A

The explanation is: The 4 ohm resistor gets shorted since current always PREFERS the low resistance path. All the current flows to the branch which is CONNECTED in parallel to the 4 ohm branch, HENCE no current flows in the 4 ohm resistance.

The correct option is (d) 0.5A

To explain I would say: SHORTING all voltage sources and opening all current sources we have:

RN=(3||6)+10 = 12 ohm.

Since the 5 ohm is the load resistance, we SHORT it and find the resistance through the short.

If we apply source transformation between the 6 ohm resistor and the 1A source, we get a 6V source in series with a 6 ohm resistor. Now we have two meshes. LET us consider I1 flowing in the first mesh and I2 flowing in the SECOND mesh.

The mesh equations are:

9I1-6I2=4

-6I1+16I2=6

On solving these equations simultaneously, we get I2=0.72A, which is the short circuit current.

Connecting the current source in PARALLEL to RN which is in turn connected in parallel to the load resistance=5ohm, we get Norton’s equivalent circuit.

Using current divider: I = 0.72*12/(12+5) = 0.5 A.

Right OPTION is (a) PLANAR circuits

Explanation: If the circuit is not planar, the meshes are not clearly defined. In planar circuits, it is EASY to DRAW the meshes HENCE the meshes are clearly defined.

Correct option is (a) Short circuit current

For EXPLANATION: Norton current is obtained by shorting the SPECIFIED terminals. So, it is the short circuit current. It is not the open circuit current because if specified terminals GET open CIRCUITED then current is equal to zero.