1.

A uniform wire is cut 10 segments increasing in length in equal steps. The resistance of shortest segment is R and the resistance of the other segments increases in steps of `4 Omega`. If the resistance of the longest segment is 2R, find the value of R and the resistance of original wire.

Answer» Resistance of first segment `= R Omega`
Resistance of second segment = `R + 4 xx 1 Omega`
Resistance of third segment `=R + 4 xx 2 Omega`
Resistance of tenth segment `= R + 4 xx 9`
`= R + 36 Omega`
As per question, `R + 36 = 2R or R = 36 Omega`
Resistance of the origin wire
`R + (R +4) + (R + 8) +(R + 12) +...`
`+ (R + 36)`
`10R +4(1+2+3+...+9)`
`=10 xx 36+4 xx 45 = 540 Omega`


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