Question

A wire when connected to 220v mains supply has power dissipation p1. Now the wire is cut into two equal parts which r connected in parallel to the same supply.Power dissipation in this case is p2 then p2:p1 is

Answer 1

V = 220v

P = p1

P = V²/R

p1 = (220)²/R

R = (220)²/p1

wire cut into two equal part

each part resistance RP = R/2 = (220)²/(2p1)

both are connected in parallel so net resistance

1/RN = 1/RP +1/RP

1/RN = 2/RP

RN = RP/2

RN =  {(220)²/(2p1)}/2

= (220)²/4p1

p2 = V²/RN

p2 = (220)²/{(220)²/4p1}

p2 = 4p1

p2/p1  = 4

p2:p1 :: 4:1

4:1 is the Answer

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