Physics · Waves · NEET
No. This is the single most important point for NEET. Electromagnetic waves (light, radio, microwaves, X-rays) can travel through vacuum. That is why sunlight and starlight reach Earth across empty space. They are made of oscillating electric and magnetic fields, so they carry their own 'medium' with them. Only mechanical waves need a material medium.
Sound is a mechanical wave (specifically a longitudinal mechanical wave). It needs a medium (solid, liquid or gas) because it travels by making the particles of the medium vibrate and push their neighbours. In vacuum there are no particles to vibrate, so sound cannot travel. Never call sound an electromagnetic wave.
Matter waves are a quantum idea, not everyday oscillations of a medium. Every moving particle (electron, proton, neutron, atom) has a wave nature with wavelength lambda = h / (m v), called the de Broglie wavelength. You cannot see them vibrate, but their wave behaviour is real and is used in devices like the electron microscope. For NEET, just remember they are associated with moving particles and come from quantum mechanics.
Sound is carried by particle-to-particle collisions, so it dies out where there are no particles (vacuum). Light is a self-sustaining oscillation of electric and magnetic fields that regenerate each other, so it does not need particles at all. This is why space is silent but not dark.
Both are mechanical waves. A string wave is a transverse mechanical wave, water surface waves are a mix of transverse and longitudinal. They need the string or water as a medium and obey Newton's laws. Do not confuse the transverse/longitudinal split with the mechanical/EM/matter split. Transverse vs longitudinal is a second, separate classification.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Mechanical waves, electromagnetic waves and matter waves. Mechanical waves need a medium and obey Newton's laws (sound, string, water). Electromagnetic waves need no medium (light, radio, X-rays). Matter waves are associated with moving particles and come from quantum mechanics.
Mechanical wave: sound in air or a wave on a string. Electromagnetic wave: light, radio waves or X-rays. Matter wave: the de Broglie wave of a moving electron.
All three transfer energy from one place to another without transferring bulk matter, and all can show wave behaviour such as reflection, interference and diffraction. What differs is whether they need a medium and what they are physically made of.
For a mechanical wave the speed depends only on the properties of the medium: its elastic property (like tension or bulk modulus) and its inertial property (like linear mass density or density). It does not depend on the speed of the source. Example: v = sqrt(T / mu) for a string.
No. Electromagnetic waves are oscillating electric and magnetic fields and always travel at c in vacuum. Matter waves are associated with particles that have mass and move slower than light; their wavelength is lambda = h / (m v). They are conceptually different.
