Which one of the following types of waves cannot propagate through vacuum and always requires a material medium for transmission?

Introduction / Context:
Waves can be broadly classified into mechanical waves and electromagnetic waves. Mechanical waves require a material medium such as air, water, or solid matter for their propagation, while electromagnetic waves can travel through vacuum. Understanding this distinction is fundamental in physics and explains why we can receive sunlight from the Sun through empty space but cannot hear sounds from outer space. This question asks which listed wave cannot travel through vacuum.

Given Data / Assumptions:

• We are comparing electromagnetic waves, light waves, sound waves, and heat radiation.
• Vacuum is a region with no matter, so no particles to vibrate.
• Mechanical waves need particle vibrations, but electromagnetic waves do not.
• Light and thermal infrared radiation are forms of electromagnetic waves.

Concept / Approach:
Sound waves are longitudinal mechanical waves resulting from pressure variations in a medium such as air or water. They rely on molecules colliding and transferring energy. Without molecules, as in vacuum, sound cannot propagate. Electromagnetic waves, including visible light and infrared radiation responsible for heat transfer by radiation, are oscillations of electric and magnetic fields and can propagate through vacuum at the speed of light. Therefore, among the options, sound waves are the only type that cannot travel through vacuum.

Step-by-Step Solution:
Step 1: Identify sound waves as mechanical pressure waves in a medium, requiring molecules or atoms to transmit disturbances. Step 2: Recognise that in vacuum there are no particles, so pressure variations cannot be transmitted and sound dies out. Step 3: Recall that electromagnetic waves such as radio waves, microwaves, infrared, visible light, ultraviolet, X rays, and gamma rays can all travel through vacuum. Step 4: Note that light waves and heat radiation are specific forms of electromagnetic waves, so they also propagate through vacuum. Step 5: Conclude that sound waves are the only listed waves that cannot propagate through vacuum.

Verification / Alternative check:
Astronauts in space rely on radios to communicate because sound cannot travel through the vacuum between spacecrafts. However, sunlight and thermal radiation reach Earth through the vacuum of space, demonstrating that electromagnetic waves do propagate without a medium. These observations match the theoretical classification and support the conclusion that sound waves need a material medium, while electromagnetic waves do not.

Why Other Options Are Wrong:
Electromagnetic waves: By definition, they can travel through vacuum at the speed of light. Light waves: Visible light is an electromagnetic wave that travels from the Sun through space to Earth. Heat radiation: Thermal infrared radiation from the Sun and other bodies reaches us through vacuum, so it does not require a material medium.

Common Pitfalls:
A common mistake is to assume that all waves need a medium because we experience sound in air. Another confusion arises between conduction, convection, and radiation as modes of heat transfer. Conduction and convection require matter, but radiation can occur through vacuum. Remember the simple rule: mechanical waves like sound need a medium, electromagnetic waves like light do not.

Final Answer:
The waves that cannot be transmitted through vacuum and always need a material medium are sound waves.