The formation of standing waves and nodes, anti-nodes is illustrated in the following diagram.
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The diagrams (a) to (e) represent the waves at successive instants as they propagate in their
respective directions. The dotted curves represent the generations of further pulses, as the particles at A & I
are allowed to vibrate further over a of time period T.
As the waves start superposing over each other at sec, the particles at E, C and G, A and I vibrate with maximum aplitude and hence anti-nodes (A-N) occur at these positions; whereas particles at D and F, B and G do not vibrate at all. These positions are called Nodes.
It should be noted that the particles where A-N are formed virate with maximum amplitude therefore for waves of frequency ≥ 10 Hz i.e. sec; these particles move from the maximum to -ve maximum along Y-axis (say) in an interval of ≥ , hence the persistence of vision gives rise to appearance of stationary loops when the standing waves are formed on strings.