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

Infrasonic sound waves have a frequency :

1. between 20 Hz to 10,000 Hz
2. below 20 Hz
3. above 20,000 Hz
4. between 20 Hz to 20,000 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.

In ancient India, dome shaped courts were built in forts to allow even the faintest of sounds to be heard from far away. Which statement best explains this effect?

1. Dome increases the frequency of the sound so it becomes louder.
2. Dome absorbs high frequency sound and re-emits it at a high amplitude.
3. Dome focuses the reflected sound and multiple reflected waves reinforce at listener's position.
4. Dome traps air thereby increasing air pressure resulting in amplification of sound.