Two Mark Question and Answers set - 1

TWO MARK QUESTION AND ANSWERS

 

1. Name different network elements.

Ans : (a) Active elements like voltage source and current source.

(b) Passive elements like resistor, inductor and capacitor.

 

2. State Ohm's law.

Ans: The ratio of the voltage across to the current through the conductor remains constant, for a constant temperature. This constant is known as resistance of the conductor.

Mathematically, V/I = constant = R

 

3. Write Kirchhoff's laws mathematically.

Ans: KCL: At electrical node, ΣI = 0

KVL: In any closed loop, Σemf + ΣIR = 0

 

4. State two salient points for a series combination of resistors.

Ans: i. Current is same and voltage is distributed

ii. The total resistance is greater than the individual resistance.

 

5. State two salient points for parallel combination of resistors.

Ans: i. Voltage is same across all individual resistance

ii. Current is divided, inversely proportional to the resistors

iii. The total resistance is less than the least.

 

6. Give two applications of both series combination and parallel combination.

Ans: For series combination :

a. A fan regulator connected in series with the fan.

b. Decoration lights.

For parallel combination

a. Electrical wiring in cinema halls

b. House wiring

 

7. A bulb is rated as 230V, 230W. Find the rated current, resistance of the filament and the energy consumed when it is operated for 10 hours.

Ans: Rated current = Power / voltage = 230/230 = 1 A

Resistance of the filament R= V/I = 230/1 = 230Ω

Energy consumed = Power x time = 230 × 10

= 2300 Wh = 2.3 KWh

= 2.3 Units

 

8. At a node there are 3 live conductors joining. The currents flowing in two conductors towards the node are 1A and 2A. What is the direction and magnitude of the current in the third conductor.

Ans: At a junction, KCL can be stated as below also Sum of incoming currents = Sum of outgoing currentsore e bomen que eobon od Tank

Here, 1+2 = Outgoing current.

In other words the current through the third conductor is 3 A flowing away from the node.

 

9. In a closed loop the algebraic sum of the elective motive forces is 10V. What is the voltage drop across resistors in that loop?

Ans: According to KVL, in any closed loop, Σemf + ΣIR = 0

⇒ 10 + ΣIR = 0

⇒ EIR = -10

The voltage drop across the resistors = 10V.

 

10. Given that the resistors Ra, R & R are connected electrically in star. Write the equations for resistors in equivalent delta.

Ans :

R_ab = R_a + R_b + R_aR_b/R_c

R_bc = R_b +R_c + R_ьR_c/R_a

R_ca R_c + R_a + R_cR_a/R_b

 

11. Three equal resistors each of R ohms are connected in star. Find the values of resistors in the equivalent delta.

Ans: R_ab = R_bc = R_ca = 3R

 

12. Three resistors R_ab, R_bc & R_ca are connected in delta. Write the expression for resistors in equivalent star.

Ans :

 

13. Three resistors, each of value R ohms are connected in delta. Find the value of resistors in its equivalent star.

Ans: R_a = R_b R_c = R/3

 

14. Write the Kirchhoff's voltage law.

Ans: The algebraic sum of electromotive forces plus the algebraic sum of voltages across impedances, in any closed circuit is equal to zero.

i.e., Σ emf+E IZ = 0, in any closed circuit.

 

15. For the circuit shown, write the nodal equations in the matrix form.

Ans: The nodes are named as shown in the given figure. Node 3 is taken as reference. In the matrix form, the nodal equations are:

 

16. Define an ideal voltage source.

Ans: For an ideal voltage source, source impedance is zero. Such voltage source gives a constant voltage V irrespective of current drawn from it.

 

17. Define an ideal current source.

Ans: For an ideal current source, source impedance is infinite. Such an ideal current source gives a constant current irrespective of voltage across it.

 

18. Draw the symbolic representation of the voltage source and current source.

Ans:

 

19. Explain how voltage source with a source resistance can be converted into an equivalent current source.

Ans: Let the voltage source have a voltage of V volts and resistance of R. R is in series with source. Its equivalent current source will have a current I in parallel with resistance R. Here,

I = V / R

 

20. Find the equivalent current source for a voltage source of 100 volts with series resistance of 22

Ans:

 

21. Write the expression for converting delta connected impedances into an equivalent star connected impedances.

Ans :

 

22. If all the three star connected impedances are identical and equal to Z, what are the delta equivalent impedances?

Ans:

Let Z_A = Z_B = Z_C = Z

Then Z_AB = Z_BC = Z_CA = 3Z

 

23. Three resistors 102, 52 and 202 are connected in star. What are the equivalent delta resistors.

Ans :

 

24. Each of the three arms of a delta connected network has resistance of 32 Find the equivalent star connected network.

Ans:

 

25. A Y-connected resistive network consists of 252 in each arm. Draw the equivalent delta- connected network and insert the values.

Ans: