JEE Main20199 Apr 2019Evening ShiftPhysicsWaves and SoundActual
A string 2.0 m long and fixed at its ends is driven by a 240 H z vibrator. The string vibrates in its third harmonic mode. The speed of the wave and its fundamental frequency is
Options
- A320    m s - 1 ,    120     H z
- B320 m s - 1 , 80 H z
- C180    m s - 1 ,    80     H z
- D180    m s - 1 ,    120     H z
Correct answer
B. 320 m s - 1 , 80 H z
Step-by-step solution
For a string fixed at both the ends, f = n 2 L v For third harmonic, 240 = 3 2 ( 2 ) v ⇒ v = 240 × 4 3 = 320    m   s - 1 Fundamental frequency f 0 = 1 2 L v = 1 4 × 320   =   80   H z