Answer:
2 times.
Explanation:
We know that f = V / λ ................. (1)
λ(a)=15 cm
λ(b)=30 cm
Va=Vb
Now by using the above formula;
f_{a} = Va/15 = Va= 15*f_{a}
f_{b} = Vb/30 = Vb = 30*f_{b}
As, Va = Vb
15*f_{a} = 30*f_{b}
f_{a} / f_{b} = 30/15
= 2 times
