Q.

There is a dual of 8 ohm resistance on the aerial. Determine the aerial’s new resistance.

1 2 Ω  
2 4 Ω  
3 7 Ω  
4 10 Ω  

Ans.

(1)

Let ( l ) be the length and ( A ) be the area of cross-section.

R=ρlA=8Ωl'=l2A'=2AR'=ρl'A'=ρl22A=14ρlA=14×8=2Ω