The condition for reflection of sound wave is :

1. surface must be smooth
2. surface must be polished
3. reflecting surface must be bigger than the wavelength of the sound wave
4. reflecting surface must be smaller than the wavelength of the sound wave

For an echo, the reflected sound must reach the person at least …………… after the original sound is heard.

1. 1 s
2. 10 s
3. 0.1 s
4. 0.01 s

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