Question

1.A 1KM long wire has a resistance of 10 ohm. what will be its resistance if the lenght is increased twice?

2. two 100 uF 63v capacitors connected in parallel.what is an assembly capacitance?

3.a 3 phase star has a connected electrical energy source has 115v measured across the A and N wires .then B to N voltage will be equal to?

Answer 1

1)Resistance is directly proportional to length R=pL/A

p=Resistivity,L=length,A =Area of cross section

So when length increases by twice,there fore length goes to 2Km.So Resistance becomes 20ohm

2)When two capacitors are in parallel their effective capacirance is equal to the Sum of their individual values.

Therefore here the capacitance of assembly would be 200uF

3)Since nothing is mentioned wether the supply is balanced or not,therefore unless stated otherwise the Supply is treated as balanced.In that case If VAn=115 V,then VBn magnitude will be also equal to 115V .Only its angle would be different from Van

Therefore if VAn=115 (Angle 0°),then VBn=115 (Angle -120°)

So VBn lags the VAn by 120 degress..

Hope this helps..