Two identical stringed instruments have frequency 100 Hz. If tension in one of them is increased by 4% and they are sounded together then the number of beats in one second is 

(1) 1

(2) 8

(3) 4

(4) 2

(4) Frequency of vibration in tight string

n=p2lTmnTΔnn=ΔT2T=12×(4%)=2%

⇒ Number of beats = Δn=2100×n=2100×100=2

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