An inductor L , 5 Ω and 10 Ω resistors are all connected in series across a voltage source v(t) = 50 cos ωt volt. If the power consumed by the 5 Ω resistor is 10 W, then the power factor of the circuit is 

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ESE Electronics 2014 Paper 1: Official Paper
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  1. 0.3
  2. 0.4
  3. 0.6
  4. 0.8

Answer (Detailed Solution Below)

Option 3 : 0.6
Free
ST 1: UPSC ESE (IES) Civil - Building Materials
20 Qs. 40 Marks 24 Mins

Detailed Solution

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Concept:

R-L Series circuit:

Since voltage across inductor leads the current through the inductor by 90° 

Vin = VR + j VL

IZ = IR + j IωL   [For series circuit current is common] 

Z = R + j X    ( ωL = XL )

By impedance triangle:

 = Power factor

Analysis:

P = I2RMS.R

10 = I2RMS. 5

I2RMS = 2

IRMS = √2 A

Im = √2× IRMS = 2A

Vm = 50∠0° 

= 25

 

= 0.6

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