To detect the obstacles in their path, bats produce:

1. Infrasonic waves
2. Ultrasonic waves
3. Electromagnetic waves
4. Radio waves.

With respect to ultrasonic waves, which of the following statements is incorrect ?

1. they travel undeviated through a long distance
2. they have a speed greater than the speed of sound in a medium
3. they are not easily absorbed in a medium
4. they can be confined to a narrow beam

The diagram shown below depicts a displacement time graph of particle a wave travelling with speed 20 m/s.

The frequency of the wave is :

1. 50 Hz
2. 33.3 Hz
3. 100 Hz
4. 1000 Hz

A girl claps in a classroom but is unable to hear an echo. Which option best explains the reason for the same ?

1. There is no reflection of sound from the walls.
2. Sound waves are completely absorbed by the walls.
3. Echo returns in less than 0.1 s.
4. Echoes require sounds of ultrasonic frequency.