Basic Electrical Engineering (BEE) - Dec 2015

First Year Engg (Semester 1)

TOTAL MARKS:
TOTAL TIME: HOURS

Solve any one question from Q1 and Q2

1 (a) Obtain the equation for coefficient of coupling between two coils placed on common magnetic field.(6 marks) 1 (b) A water pump lifts 50 m³ of water per hour to a height of 20 m. The overall efficiency of water pump set is 0.60. Find monthly bill, when the pump is used 4 hours a day for a month of 30 days, at the rate of Rs. 5/kWh.(6 marks) 2 (a) Explain the effect of temperature on resistance of:
(i) metal conductors
(ii) insulators
(iii) alloys.(6 marks) 2 (b) A steel ring of mean diameter of 50 cm is wound with 500 turns on it. A flux density of 1 Tesla is produced in the ring by mmf of 4000 AT/m. Calculate magnetising current. Also find the current when an air gap of 1 mm is cut in it, keeping B = 1 Tesla in the ring.(6 marks)

Solve any one question from Q3 and Q4

3 (a) Obtain the expression for composite capacitor having 3-dielectric materials.(7 marks) 3 (b) A 50 Hz sinusoidal voltage has rms value of 200 V. At t = 0, the instantaneous value is positive and half of its maximum value. Write down the expression for voltage and sketch the wave form.(6 marks) 4 (a) Derive an equation for average value of sinusoidal current in terms of its peak value.(6 marks) 4 (b) A 40 kVA, 2200/220 V, 50 Hz, 1-ph transformer has an iron loss of 250 W. The resistances of low and high voltage windings are 0.005 Ω and 0.5 Ω respectively. Calculate efficiency at full load and load p.f. = 0.8 lagging.(7 marks)

Solve any one question from Q5 and Q6

5 (a) Obtain the expression for power, if x = v_m sin out is applied to R-L series circuit.(6 marks) 5 (b) Three identical impedances each of 6 + j8 Ω are connected in star across 3-ph, 400 V, 50 Hz a.c. supply. Calculate:
(i) line current
(ii) active power
(iii) reactive power.(7 marks) 6 (a) What is series resonance? Obtain the equation for resonant frequency.(6 marks) 6 (b) Two circuits having impedances Z₁ = 8 + j6 Ω and Z₂ = 5 +j10 Ω are connected in parallel across 200 V, 50 Hz, 1-ph a.c. supply. Calculate:
(i) current drawn by each circuit
(ii) total current
(iii) p.f. of whole circuit.(7 marks)

Solve any one question from Q7 and Q8

7 (a) Using simple series-parallel combination, find R_BC for Fig 1. (6 marks) 7 (b) Obtain the equations to convert A-connected resistances into equivalent star circuit.(6 marks) 8 (a) State the Thevenin's theorem and explain the steps to find R_th, V_th and I_th.(6 marks) 8 (b) Using Mesh/Loop analysis, calculate current flowing through R_BC for Fig 2. (6 marks)