Which of the following waves is not mechanical?

Step 1: Analyze the question We need to find the wave that is not mechanical.

Step 2: The concept

• Mechanical waves need a material medium (solid, liquid, or gas) to travel. The particles of the medium vibrate to pass on the energy. Examples are sound waves, water waves, waves on strings, and seismic waves.
• Electromagnetic waves do not need a medium. They are made of oscillating electric and magnetic fields and can travel through a vacuum. Examples are radio waves, light, X-rays, and gamma rays.

Step 3: Check each option

• A. Waves in pipes: These are sound waves, where air in the pipe vibrates. They need a medium, so they are mechanical.
• B. Water waves: The water particles move up and down. They need a medium, so they are mechanical.
• C. Radio waves: These are part of the electromagnetic spectrum. They travel through a vacuum, which is how signals reach us from satellites. They are not mechanical.
• D. Sound waves: These are longitudinal waves that cannot travel in a vacuum. They are mechanical.

Step 4: Answer The wave that is not mechanical is radio waves, which is option C.

Exam tip: Remember "EM = No Medium needed." If a wave is in the electromagnetic spectrum (radio, microwave, infrared, visible light, ultraviolet, X-ray, gamma), it is not mechanical. If you can hear it or see it move through matter (sound, water, rope, earthquake), it is mechanical.