A key of mechanical piano is first struck gently and then struck again but much harder this time. In the second case:

When we change a feeble sound to a loud sound, we increase its:

Before playing the orchestra in a musical concert, a sitarist tries to adjust the tension and pluck the strings suitably. By doing so he is adjusting:

One of the following can hear infrasound. This one is:

The speed of highly penetrating ultrasonic waves is: