ELE101 : Electrical Science - I Question Paper

PART-A

Question 1 : [10]
(A)why transformers are related in KVA instead of KW?

(B)How can we improve the power factor in electrical circuit?

(C)What is the difference between true power,reactive power and apparent power?

(D)Why is MOFSET sometimes called IGFET?

(E)Why FET is called voltage controlled device?

Question 2 : [15]
(A)A mild steel ring of 30cm mean circumference has a cross sectional area of 6cm*cm and has a winding of 500 turns on it.The ring is cut through at a point so as to provide an air gap of 1mm in magnetic circuit.It is found that a current of 4A in the winding, produces a flux density of 1T in the air gap.Find:
(a)Relative Permeability of mild steel.
(b)inductance of the winding.

(B)A transistor has an emitter current of 10mA and a collector current of 9.5mA.Calculate the base current, current amplification factor and transport factor.

(C)In a moving coil instrument,the moving coil consist of 100 turns wound on a square former of length 3cm.The Flux density in air gap is 0.06T.Calculate the turning moment acting on the coil when carrying a current 0f 12mA.

(D)If 20ohms(each) resistances are connected in delta connection,what will be the value of resistances
if they are now connected in star connection.

(E)Calculate the reading which will be given by hot wire voltmeter if it is connected across the terminals of generator whose voltage waveform is given by:
"V=200?t+100sin3?t+50sin5?t"

PART-B

Question 3 :
(A)What are the advantages of electrical transducers over other transducer.[5]

(B)By considering a practical application discuss the working of LVDT.Give atleast six merits and demerits of LVDT.[10]

Question 4 :
(A)Explain the resonance curve for series RLC circuit.Clearly mention the significance of each region.[10]

(B)What are the requirement to produce 10V(dc)regulated from 220V(ac)supply.Draw the single line diagram and give significance of each part.[5]

PART-C

Question 5:
Two impedance Z1 ANd Z2 when Connected separately across a 230V,50Hz supply consumed 110W and 60W at a a power factor of 0.5 lagging and 0.6 lagging leading respectively.If these impedances are now connected in series across the same supply.Find: [15]

(a)Total power absorbed and overall power factor.
(b)The value of impedance to be added in series so as to raise the overall power factor to infinity.

Question 6 : A single phase 100Kva,3300/230V.50Hz transformer has 89.5% efficiency at 0.85 lag power factor both at full load and half load..Determine the efficiency of transformer at 75% load and

Question 7:
A bridge rectifier is applied with input from a step down transformer having turns ratio 1:8 and input 230V,50Hz.If the diode forward resistance is 10ohm,secondary resistance is 10ohms and the load resistance is 10ohms .

Find:
(a)DC out power.
(b)PIV across each diode.
(c)% Efficiency.