Various types of mechanical waves are :

1. electromagnetic, longitudinal, transverse
2. electromagnetic, transverse
3. longitudinal, transverse
4. electromagnetic, transverse.

Due to vibrations of medium particles, the energy transformation is from :

1. heat energy to kinetic energy and vice versa
2. kinetic energy to potential energy and vice versa
3. heat energy to potential energy and vice versa
4. potential energy to nuclear energy and vice versa

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