Answer :
The frequency of driver is 700 Hz
Explanation:
The frequency of wave in a string is given by the relation
n = [tex]\frac{p}{2l} \sqrt{\frac{T}{m} }[/tex]
here n is the frequency
p is the number of antinodes and l is the length of string .
T is the tension in string and m is the mass per unit length
Thus 420 =[tex]\frac{3}{120} \sqrt{\frac{T}{2} }[/tex] I
Now if there is 5 antinodes , the value of p = 5
Thus n = [tex]\frac{5}{120} \sqrt{\frac{T}{2} }[/tex] II
Dividing II by I , we have
n/420 = 5/3
or n = 5/3 x 420 = 700 Hz