Question

For a standing wave mode on a string fixed at both ends, adjacent antinodes are separated by a distance of 20 cm. Waves travel on this string at a speed of 1200 cm/s. At what frequency is the string vibrated to produce this standing wave?

(A) 120 Hz 

(B) 60 Hz 

(C) 40 Hz 

(D) 30 Hz 

(E) 20 Hz

Answer 1

The correct option is: (D) 30 Hz 

Explanation:

Two antinodes by definition will be ½ λ apart. So 20 cm = ½ λ, and the λ = 40 cm. Then using v = f λ we have 1200 = f (40)