Bangalore University 2006-2nd Sem B.E Electrical and Electronics Engineering First /BE ,/ - Question Paper

NEW SCHEME
First / 2nd Semester B. E. Degree Examination, January / February 2006
Common to All Branches
Basic Electrical Engineering
Time: three Hrs.] [Max. Marks: 100

Note: 1. ans any 5 full ques..

1. (a) Derive the expression for the energy stored in a magnetic field.
(b) A flux of 0.5mwb is produced in a coil of 900 turns would on a wooden ring by a current of 3A. compute.
i) Inductance of the coil.
ii) Average e.m.f. induced in it when a current of 5A is switched off, assuming the current to fall to zero in 1ms.
iii) The mutual inductance ranging from the coils, if a 2nd coil of 600 turns was uniformly wound over the first. (6 Marks)

(c) In a circuit supplied from 50Hz the voltage and current have maximum values of 500V and 10A respectively. AT t=0, their respective values are 400Va dn 4A both increasing positively.
i) Write expressions for their instantaneous values.
ii) Find the angle ranging from V and I and
iii) I at t=0.015 sec. (8 Marks)

2. (a) Show that the avg. power is a pure inductance with a sinusoidal voltage is zero. (5 Marks)

(b) The formula of an alternating current is provided by i=42.42 sin628t. compute its
i) Maximum value ii) Frequency iii) RMS value
iv) avg. value v) Form factor. (5 Marks)

(c) 2 circuits with impedances of Z1 = (10 + j15) O and Z2 = (6-j8 j8) O are connected in parallel. If the supply current is 20A, what is the power dissipated in every branch? (10 Marks)

3. (a) Show that in a three phase balanced circuit 2 wattmeters are sufficient to measure the total 3 phase power and power factor of the circuit.(10 Marks)

(b) A balanced star connected load of (8+j6) O per pahse is connected to a 3 phase, 230V supply. obtain the line current, power factor, power reactive voltampere and total voltampere. (10 Marks)

4. (a) With a neat sketch discuss the construction and working of a single phase, induction kind energy meter. (8 Marks)

(b) With a neat diagram and switching table discuss 2 point control of lamp (6 Marks)

(c) With a neat sketch discuss any 1 method of earthing. (6 Marks)

5. (a) Draw the schematic representation of series, shunt and long-shunt compound generators. In every case, write the voltage balance and current balance equations. (6 Marks)

(b) provide reasons:
i) The armature winding is placed on the rotor in a dc machine.
ii) Shunt motors are used for constant speed applications.
iii) Series motors should not be started without proper load. (6 Marks)

Earning:   Approval pending.