1.

Two wires of same radius having lengths l_1, and l_2 and resistivities rho_1 and rho_2 are connected in series. The equivalent resistivity will be

Answer»

`(rho_1l_2+ rho_2 l_1)/( RHO _1+ rho_2)`
`(rho_1l_1+ rho_2 l_2)/( l _1+l _2)`
`(rho_1l_1+ rho_2 l_2)/( l _1- l_2)`
`(rho_1l_2+ rho_2 l_1)/( l _1+ l_2)`

Solution :In seriesequivalentresistances
` R = R_1+R_2`
HENCE ` R_1 =( rho _1 l_1)/(A) .R_2 = ( rho _2 l_2) /(A), R = (rho (l_1+l_2))/( A)`
` THEREFORE(rho(l_1 +l_2))/(A)=( rho_1 l_1)/( A)+ (rho _1l_1)/(A)+( rho _1 l_2)/( A) =rho= (rho _1 l_1+rho_2l_2)/( l_1l_2)`


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