WHAT IS STANDING WAVE?

STANDING WAVES ARE  THE SUPERPOSITION OF TWO WAVES WHICH ARE OF THE SAME AMPLITUDE AND SAME FREQUENCY BUT PROPAGATING IN THE OPPOSITE DIRECTIONS.

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In Figure 4, a pulse generated by a flip of the string on the left travels to the right end, which is fixated to a wall. The pulse then reflects upside down from the fixed end. 

Figure 4 A wave pulse reflects from a fixed barrier.

Now, suppose that pulses are sent along the string at regular time intervals. The reflected pulse traveling to the left adds to the original pulse traveling to the right toward the wall. Standing waves are produced by the superposition of these similar but inverted pulses that are traveling in opposite directions.