Fundamental frequency of sonometer wire is n. If the length, tension and diameter of wire are tripled, the new fundamental frequency is
n3
n33
n=12lTπr2ρ⇒n∝Tlr⇒n1n2=T1T2×l2l1×r2r1
=T3T×3ll×2rr=33⇒n2=n33