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A wire P has resistance of 20 ohm. Another wire Q of same material but length twice that of P has resistance of 8 ohm. If r is the radius of cross-section of P, the radius of cross-section of Q is |
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Answer» `r`  The wire Q has resistance of `8Omega`. Let its length be 2l. Let the unknown radius be `r_(Q)`. `R_(Q)=(rho2l)/(pir_(Q)^(2))""...(ii)`<  DIVIDE (i) by (ii) we get `(R_(P))/(R_(Q))=(r_(Q)^(2))/(2r^(2))or(20)/(8)=(r_(Q)^(2))/(2r^(2))orr_(Q)^(2)=5r^(2)orr_(Q)=sqrt(5)r` |
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