Answer:
(a) increase by
times
Step-by-step explanation:
Natural frequency of a wave in a string is given by:
![f = (1)/(2L)\sqrt{(T)/(\mu)}](https://img.qammunity.org/2020/formulas/physics/high-school/5uhgxjsstr3lirkmoybnzg9d8vtcuwk09e.png)
where, L is the length of the string, T is the tension in the string and
is the linear density of the string.
Considering the length and linear density of the string are constant, if the tension in a string is doubled, the natural frequency of the string would:
![f\propto √(T)](https://img.qammunity.org/2020/formulas/physics/college/c8ejniedor2jqhdyk1v9mezg9aod4r073y.png)
![(f_n)/(f)=\sqrt{(T_n)/(T)}\\ \Rightarrow f_n =\sqrt{(2T)/(T)}f = √(2) f](https://img.qammunity.org/2020/formulas/physics/college/s67m1tqeu9momjz5j4liiz1fqr4jw4g5cp.png)
Thus, the natural frequency of the string would increase by
times.