CBSE Class 11-science Answered

When two sets of progressive waves of the same type having the same amplitude and same time period/frequency/waveelength travelling with same speed along the same straight line in opposite directions superimpose, a new set of waves are formed. which are called stationary waves. The resultant waves do not propagate in any direction, nor there is any transfer of energy in the medium. In the stationary wave, there are certain points of the medium, which are permanently at rest i.e. their displacement is zero all throughout. These points are called nodes. And there are some other points which vibrate about their mean position with largest amplitude. These are called antinodes.

 

For more on standing waves, you may referto the following link:

http://www.topperlearning.com/student/topic/NTcw/CBSE-Class%20XI-Physics-Waves-Standing%20waves