question_answer

A metal wire of linear mass density of \[9.8\] g/m is stretched with a tension of 10 kg-wt between two rigid supports 1 m apart. The wire passes at its middle point between the poles of a permanent magnet and it vibrates in resonance when carrying an alternating current of frequency n. The frequency n of the alternating source is                [AIEEE 2003]

A)  50 Hz              

B)  100 Hz

C)  200 Hz                        

D)  25 Hz

Correct Answer: A

Solution :

[a] The wire will vibrate with the same frequency as that of source. This can be considered as an example of forced vibration.

,

Frequency of wire,

(where, m = mass/unit length)

= 50 Hz