Bangalore University 2005-2nd Sem B.E Electrical and Electronics Engineering First/ester , ruary/ch - Question Paper

First/Second Semester B.E. Degree Examination, February/March 2005
Common to all branches.
(New Scheme)
Basic Electrical Engineering

Time: three Hrs.] [Max. Marks: 100

Note: ans any 5 full ques..


1. (a) discuss Fleming’s rules as applied to Induced emf’s (5 Marks)
(b) Define:
i) Self Inductance and
ii) Mutual inductance and find the relationship ranging from these two. (8 Marks)

(c) describe RMS and avg. value of a sinusoidally varying current and obtain their values in terms of its peak value. (7 Marks)

2. (a) Show that the avg. power in a pure capacitive circuit with a sinusoidal voltage is zero. (6 Marks)


(b) A coil of power factor 0.6 is in series with a 100µf Capacitor. When connected to a 50Hz supply, the potential difference across the coil is equal to the potential difference across the capacitor. obtain the resistance and inductance of the coil. (9 Marks)

(c) 2 impedances (150 + j157) O are connected in parallel across a 220V, 50H = supply. obtain the total current and power factor. (5 Marks)

3. (a) Derive the relationship ranging from the line and phase volumes of a balanced star connected lead. (6 Marks)

(b) 3 100 O resistors are connected in i) Star & ii) Delta across a 415V. 50Hz, 3-phase supply. compute the line and phase currents and the power consumed in every case. (6 Marks)

(c) Estimate the power factor in every of the subsequent cases of 2 Wattmeter method of measuring 3 phase power:

i) Wattmeter readings are equal
ii) Wattmeter readings are equal and opposite.
iii) Wattmeter studying are in the ratio 1:2
iv) One wattmeter reads zero. (6 Marks)

4. (a) discuss the following:
i) Armature winding of a DC machine
ii) Commutator of a DC machine
iii) Brushes of a DC machine (6 Marks)

(b) discuss the significance of back emf in de motors. (4 Marks)

(c) A 4-pole 250V series motor has wave connected armature with 1254 conductors. The flux per pole is 22wb. When the motor is taking 50A. The armature and series field coil resistances are respectively 0.3 O and 0.2 O. compute the speed and torque of the motor and also the power developed in watts.
(10 Marks)

5. (a) Draw the typical speed/load characteristics of i) shunt and ii) Series motors and draw the comments on their shapes ad mention the applications of these motors. (10 Marks)

(b) discuss the need of starter for DC motors. (5 Marks)

(c) A series motor should never be started without a load on it. Justify this statement. (5 Marks)


6. (a) elaborate the losses in a transformer? On what factors do they depend? And how are they minimised? (6 Marks)

(b) A single phase transformer has 400 primary and 1000 secondary turns. The net cross sectional area of the core is 60 cm2 . The supply is 500V. 50Hz. Calculate:

i) The peak value of flux density
ii) Voltage induced in the secondary and
iii) The number of secondary turns to induce a voltage of 2500V (6 Marks)

(c) Derive an expression of or the terminal voltage on no load of a star connected 3 phase alternator. (6 Marks)

7. (a) discuss how torque is produced in a 3 phase induction motor (6 Marks)

(b) A 3 phase 10 pole induction motor is supplied by a 6-pole alternator running at 1200 rpm. compute the speed of the motor for a slip of three percent. (6 Marks)

(c) obtain the number of armature conductors in series per phase of a 3 phase. 50Hz, 10 pole alternator having 90 slots. The winding is to be star connected to provide a line voltage of 11kV. When the flux is 160 mwb. The winding factor is unity. Also obtain the voltage regulation when the full load terminal voltage is 10.60 KV. (8 Marks)

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

(b) discuss the various kinds of wiring used in practice. (6 Marks)

(c) discuss the brief:

i) fuses
ii) Specification of wires
iii) Earthing and its necessity. (6 Marks)

Earning:   Approval pending.