When sound travels in form of a wave:

1. the particles of medium move from the source to the listener
2. the particles of medium remain stationary
3. the particles of medium start vibrating up and down
4. the particles of medium transfer energy without leaving their mean positions.

The safe limit of loudness of audible sound is:

1. 0 to 80 dB
2. above 80 dB
3. 120 dB
4. above 120 dB

The unit of loudness is:

1. cm
2. second
3. hertz
4. decibel

In a piano, pitch is decreased by:

1. using thicker string
2. increasing tension
3. reducing length of string
4. striking it hard