The sound of frequency less than 20 Hz is called :

1. supersonic
2. infrasonic
3. ultrasonic
4. ultrasound

The properties of ultrasound that make it useful, are:

1. High power and high speed
2. High power and good directivity
3. High frequency and high speed
4. High frequency and bending around the objects

Assertion (A) : Sound waves cannot travel through vacuum.

Reason (R) : Sound travels in the form of longitudinal waves.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false

Assertion (A) : The speed of sound is maximum in gases when compared with speed in solids.

Reason (R) : The speed of sound in a medium depends on the density of medium.

1. both A and R are true and R is the correct explanation of A
2. both A and R are true and R is not the correct explanation of A
3. assertion is false but reason is true
4. assertion is true but reason is false