Physics · Waves · NEET
Because only the disturbance travels, not the material. NCERT gives the exact proof: drop a pebble in a pond and place cork pieces on the surface. The circular ripples move outward, but the cork only bobs up and down about its own spot and never drifts to the edge. The water particles pass energy to their neighbours and then return, so the pattern advances while the matter stays put.
The disturbance (the shape or pattern) and the energy it carries move. Each particle pushes the next particle, hands over energy, and comes back to rest. The 'wave' you see moving is this hand-over of energy passing from particle to particle, like a Mexican wave in a stadium where people stand and sit but stay in their seats.
Air molecules near the source vibrate back and forth and push the next layer of air, which pushes the next, and so on. Energy is passed along, but no single air molecule travels from the speaker into your ear. If air actually flowed, you would feel a wind, not hear a sound. This is why waves are said to transport energy, not matter.
No. A wave is not a thing, it is a process, a disturbance that propagates. You cannot store a wave in a box. What exists is the medium (water, air, string) plus the moving pattern of energy passing through it. For NEET, remember the definition: a wave is a disturbance that travels through a medium carrying energy without net transfer of matter.
Mechanical waves (sound, water, waves on a string) need a material medium because particles must push neighbours. Electromagnetic waves (light, radio) do NOT need a medium and can travel through vacuum. In every case, the wave still carries energy, not matter. The medium requirement is the difference explored in the next concept.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
A wave is a disturbance that travels through a medium (or vacuum for EM waves) and transports energy and information without any net transfer of matter.
Waves transfer energy (and information), not matter. The particles of the medium only vibrate about their mean positions and return, they do not move along with the wave.
NCERT's cork experiment: cork pieces on disturbed pond water only move up and down about a fixed point while the ripples spread outward. The pattern (and its energy) travels, the water does not flow outward.
No. Mechanical waves like sound and water waves need a medium, but electromagnetic waves like light travel through vacuum. Both types still carry energy, not matter.
The wave (the disturbance) moves steadily forward through the medium, but each particle just oscillates back and forth or up and down about its own fixed mean position. The two motions are different, which is covered in the particle velocity vs wave velocity concept.
