Download WBUHS 2nd Year 2022 May Microbiology Paper I Question Paper

3. Answer all questions in Part A.

4. Part B consists of 5 units. Answer any one full question from each unit i.e., one from ‘either’ ‘or’ choice. Each question carries 10 marks.

PART – A

(10 x 2 = 20 Marks)

1. 1. Define active and passive elements.
   2. State Ohm’s Law and mention its limitations.

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   3. Define Average value and RMS value of an alternating quantity.
   4. Define Power factor. What is its importance?
   5. What are the advantages of three-phase system over single-phase system?
   6. Write the relationship between line and phase voltages and currents in star and delta connected systems.
   7. Why is transformer rating expressed in KVA?

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   8. What are the losses occurring in a transformer?
   9. What is the function of commutator in a DC machine?
   10. Why is a starter necessary for a DC motor?

PART – B

(5 x 10 = 50 Marks)

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UNIT-I

1. (a) Using Kirchhoff’s laws, determine the current flowing through each branch of the network shown in Figure 1.

   (b) Find the equivalent resistance between A and B in the circuit shown in Figure 2 using star-delta transformation.

   OR

2. (a) State and explain superposition theorem.

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   (b) Find the current through 5Ω resistor using Thevenin’s theorem for the circuit shown in Figure 3.

UNIT-II

3. (a) Define and derive the expression for the form factor and peak factor.

   (b) A 230 V, 50 Hz AC supply is applied to a coil of 0.06 H inductance and 2.5 Ω resistance connected in series. Calculate (i) Impedance (ii) Current (iii) Phase angle between voltage and current (iv) Power factor (v) Power consumed.

   OR

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4. (a) Explain the concept of resonance in series RLC circuit. Derive the expression for resonant frequency.

   (b) A coil of resistance 20 Ω and inductance 0.2 H is connected in series with a capacitor of 100 μF. The circuit is connected to a 230 V, 50 Hz supply. Calculate (i) Impedance (ii) Current (iii) Power factor (iv) Voltage across the coil (v) Voltage across the capacitor.

UNIT-III

5. (a) Derive the relationship between line and phase voltages and currents in a three-phase delta connected system.

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   (b) Three identical coils, each having a resistance of 20 Ω and inductance of 0.06 H are connected in delta to a 400 V, 50 Hz, 3-phase supply. Calculate the line current and the power absorbed.

   OR

6. (a) Explain the two-wattmeter method for measuring power in a three-phase balanced system.

   (b) The power input to a 3-phase induction motor is measured by two wattmeters. The readings of the wattmeters are 5 kW and -1.5 kW. If the supply voltage is 400 V and the motor is delta connected, calculate (i) The total power (ii) Power factor (iii) Line current.

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UNIT-IV

7. (a) Explain the working principle of a single-phase transformer with a neat sketch.

   (b) A 200 kVA, 3300/240 V, 50 Hz single-phase transformer has 90 turns on the secondary winding. Calculate the number of turns on the primary winding, the primary and secondary full load currents. Neglect losses.

   OR

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8. (a) Derive the EMF equation of a single-phase transformer.

   (b) A 200 kVA, 11000/400 V, 50 Hz single-phase transformer gave the following test results:

   O.C. Test (LV Side): 400 V, 8 A, 1.0 kW

   S.C. Test (HV Side): 600 V, 18.2 A, 5.3 kW

   Determine the efficiency at full load and 0.8 power factor lagging.

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UNIT-V

9. (a) Explain the working principle of a DC generator with a neat sketch.

   (b) A 4-pole, lap-wound DC generator has 400 conductors. The flux per pole is 0.02 Wb. Calculate the EMF generated when the generator is running at 1200 rpm.

   OR

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10. (a) Explain the working principle of a DC motor with a neat sketch.

    (b) A 220 V DC shunt motor takes a current of 4 A on no-load. The armature resistance is 0.8 Ω and shunt field resistance is 220 Ω. Estimate the efficiency when the motor takes a current of 60 A on load.

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