Two Marks Questions And Answers

TWO MARKS QUESTIONS AND ANSWERS

1. Define alternating current.

An alternating current is the current which changes its magnitude and direction at regular interval of time.

2. Define frequency.

The total number of cycles made by alternating quantity per second is known as frequency. The unit of frequency is Hertz and is denoted by f.

3. Define time period.

The time taken by an alternating quantity to complete its one cycle is known as its Yo time period. It is denoted by T seconds. loved to) noizzare

4. Define amplitude.

The maximum value attained by an alternating quantity during positive or negative half cycle is collect its amplitude.

5. Define average value.

It is defined as the valve of AC current flowing through a given resistance for a given time produces same charge as produced by the direct current when flowing through the same resistance for the same time.

6. Define RMS valve.

It is the valve of an alternating quantity and is defined as AC value of current flowing through a given resistance for a time produces the same amount of heat as produced Isbio by the direct current when flowing through the same resistance for the same time,

7. What is meant by form factor?

Form factor is the ratio of RMS valve to the average value,

8. What is meant by Peak Factor?

It is defined as the ratio of maximum value to the rms value.

9. Define capacitance.

It is defined as the charge developed to that of voltage applied to it:

C= q/V

10. Give the expression for the voltage and current in an inductor (or) capacitor.

11. Define power factor.

Power factor is defined as the cosine of the angle between voltage and current.

Power factor = cos Φ = True power / Apparent power

12. Define phasor diagram.

The diagram in which different alternating quantities of the same frequency, sinusoidal in nature are represented by individual phasors indicating exact phase inter- relationships is known as phasor diagram.

13. What is meant by unity power factor?

If the current and voltage are in same phase then it is said to be unity power factor

14. What is meant by impedance?

Impedance is defined as the ratio of voltage to that of current

Z = V/I.

15. Draw voltage and power triangle.

16. Define active, reactive and apparent power.

Active power is defined as the power consumed by the active element like resistance. It is measured in watts.

P = VI cos Φ (W)

Reactive power is defined as the power consumed by the reactive element like capacitor and inductor. It is measured in VAR.

Q = VI sin Φ (VAR)

Apparent power is defined as the product of voltage and current. It is measured in slim Volt Ampere.

S = VI (VA)

17. What is meant by resonance?

It is the condition of an RLC circuit at which inductive reactance is equal to capacitive reactance

X_L = X_C

18. Define bandwidth.

It is defined as the difference between the frequencies f₁, and f₂.

Bandwidth = f₂-f₁ = R/2πL

19. Define quality factor.

It is defined as the ratio of resonant frequency to that of bandwidth.

20. What is amplitude factor?

It is the ratio of maximum value to the RMS value. It is also called as crest factor or peak factor.

K_a Maximum value /RMS value

21. Define Kirchoff's Voltage law.

Kirchoff's law can be stated in words as the sum of all voltage drops and rises in a closed loop equals zero. Sum of voltages around a closed path is equal to zero.

22. Explain the concept of current division in a circuit.

The current in various branches can be found out if the total current and branch resistances are known.

23. A bulb is rated as 230 V, 230 W. Find the rated current and resistance of the filament.

P = VI  I=P/VI= 230/230

I=1A P=I²RR = P/I²

R = 230/I   R = 230 ohms.

24. Define Mesh analyses of a circuit.

The Mesh Current Method, also known as the Loop Current Method, is quite similar to the Branch Current method in that it uses simultaneous equations, Kirchhoff's Voltage Law, and Ohm's Law to determine unknown currents in a network. It differs from the Branch current method in that it does not use Kirchoff's Current Law, and it is usually able to solve a circuit with less unknown variables and less simultaneous equations, which is especially nice if you're forced to solve without a calculator.

25. What is meant by linear and non-linear elements?

Linear element shows the linear characteristics of voltage Vs current.

Non-linear element the current passing through it does not change linearity with the linear change in applied voltage at a particular frequency.

26. What is meant by unilateral and bilateral elements?

If the magnitude of the current passing through an element is affected due to change in the polarity of the applied voltage is called unilateral elements.

If the current magnitude remains the same even if the applied EMFS polarity is changed is called bilateral elements.

27. Define Ohms Law.

The potential difference across any two ends of a conductor is directly proportional to the current flowing between the two ends provided the temperature of the conductor remains constant.

28. Mention the disadvantages of Ohm's Law.

It does not apply to all non-metallic conductors.

 (a) It also does not apply to non-linear devices such as zener diode, vacuum tubes etc.

(b) It is true for metal conductors at constant temperature. If the temperature changes the law is not applicable.

29. What is a node, a junction and a branch?

A node of a network is an equipotential surface at which two or more circuit elements are joined.

A junction is that point in a network where three or more circuit elements are joined.

A branch is that part of a network which lies between two junction points.

30.Write the equation for Instantaneous active power, average power, and apparent power.

Instantaneous active power,

31. Compare series and parallel circuit.

32. What is a planar circuit?

A circuit is said to be non-planar if it cannot be drawn on a plane surface without crossovers.

33. State the limitations of ohms law.

(1) It cannot be applied for non-metallic conductors.

(2) Ohm's law is not applicable to all non-metallic conductor.

(3) If is also not applicable to non-linear devices. Such as diodes, transistors and other semiconductor devices.

34. Two resistance of 4 Ω and 6 Ω are converted in parallel across 10 V battery. Determine the current through 6 Ω resistance.

35. A50 Ω resistor is in parallel with a 100 Ω resistor. The current in 50 Ω resistor is 7.2 A. What is the value of third resistor to be added in parallel to make the total line current as 12.1 A?

36. Define line current and phase current.

The current flowing through the line is called line current.

The current flowing through the phase is called phase current.

37. Define line and phase voltage.

The voltage between two lines is called the line voltage.

The voltage between any line and the neutral point is called phase voltage.

38. Give the line and phase values in star connection.

The relation between line and phase voltage in star connection is:

E_L = √3E_ph

The relation between line current and phase current in a star connection is:

I_L = Iph

39. Give the line and phase values in delta connection.

The relation between line voltage and phase voltage in a delta connection is:

E_L = E_ph

The relation between line current and phase current in delta connection is:

I_L = √31_ph

40. Write few methods available for measuring in 3-phase load.

* One wattmeter method

* Two wattmeter method

* Three wattmeter method

41. List the methods used for power measurement with single wattmeter.

* Potential lead shift method

* T-method

* Artificial Neutral Method

* Current Transformer Method

 

 

PART-B QUESTIONS

1. Show that the resonance frequency of a series RLC circuit is Also derive the expression for Q factor.

2. Distinguish between (i) Apparent power, (ii) Active power, (iii) Reactive power in AC circuits.

3. Find loop currents by mesh analysis for the circuit shown below.

4. In the circuits shown find the current I by the mesh method.

5. Write the nodal equations for the network. Hence find the potential difference between nodes 2 and 4.

6. Determine the current delivered by the source in the circuit shown in figure below.

7. For the network shown below, obtain the current ratio (I₁/I₂) using mesh analysis.

8. Find the current through each branch by network reduction technique.

9. For the circuit shown in figure, find the (i) currents in different branches, (ii) current supplied by the battery, (iii) potential difference between terminals A and B.

10. In the circuits of figure, find the current I by the mesh method.

11. (i) State and explain Kirchoff's laws.

(ii) Using mesh analysis determine the current through 1Ωresistor in the circuit shown.

12. By applying nodal analysis for the circuit shown in figure. Determine the power output of the source and the power in each resisto n resistor of the circuit.

13. Using nodal analysis, find the node voltages and the currents through all the resistors for the circuit shown in figure.

14. Find the node voltages V₁ and V₂ and also the current supplied by the source for the Jioni circuit shown below.

15. (i) State and explain kirchoff's laws.

 (ii) Four resistances of values 2, 3, 4 and 5 ohms are in parallel with a common supply. If the total power absorbed in all of them is 4620 watts, find the applied voltage and the power absorbed in each resistor.

16. Explain different types of voltage and current sources.

17. Find the current I and voltage across 30 ohm of the circuit shown in figure.

18. Determine the current in all the resistors of the circuit shown in figure.

19. (a) Use the branch currents in the network shown below to find the current supplied by the 60V source. Solve the circuit by mesh current method:

(b) Solve the network given below by the node voltage method:

20. Using node analysis, find the voltage V for the circuit shown in figure below:

21 With a neat circuit and phasor diagram explain the three phase power measurement by two wattmeter methods.

22. (i) A symmetrical three phase 400 V system supplies a balanced delta connected load. The current in each branch circuit is 20 A and phase angle 40° (lag). Calculate the line current and total power.

(ii) A three phase delta connected load has Z  (100+ j0) ohms, Zbe = (-j100) (70.7-j70.7) ohms is connected to a balanced 3 phase 400 V bailqque supply. Determine the line currents I, I, and I. Assume the phase sequence :bodiem inst deem yd tius abc

23. (i) A balanced three phase star connected load with impedance 8+j6 ohm per phase is connected across a symmetrical 400 V three phase 50 Hz supply. Determine the line current, power factor of the load and total power.

(ii) An alternating current is expressed as i = 14.14 sin 314t. Determine rms current, frequency and instantaneous current then t = 0.02 ms. (8)

24. (i) A balanced star connected load of 4 + j3 ohm per phase is connected to a 400 V, volt ampere (8)

 (ii) A voltage source 100 V with resistance of 10 ohms and inductance 50 mH, a capacitor 50 microfarad are connected in series. Calculate the impedance when the frequency is (i) 50 Hz, (ii) 500 Hz, (iii) the power factor at 100 Hz. (8)

25. (i) Three impedances Z, = 3 45° ohm, Z = 10 √2 45° ohm, Z, 5-90° ohm are connected in series. Calculate applied voltage if voltage across Z1 = 27 <-10°V.

(ii) A delta connected load as shown in figure is connected across 3 phase 100 volt wolsd guilov sril supply. Determine all line currents.