Which of the following is/are longitudinal wave(s)? I. Light waves from the sun II. Sound waves in the air III. Waves on a vibrating string

Step 1: Analyze the question We need to identify which of the three waves are longitudinal, meaning the particles of the medium (or the oscillating quantity) vibrate parallel to the direction the wave travels.

Step 2: The concept

• Longitudinal waves: vibration is parallel to the direction of travel. They form compressions and rarefactions. Examples: sound waves, and waves in a slinky pushed back and forth.
• Transverse waves: vibration is perpendicular to the direction of travel. Examples: light and all electromagnetic waves, waves on strings, and water surface ripples.

Step 3: Check each statement

• I. Light waves from the sun: These are electromagnetic waves. The electric and magnetic fields oscillate perpendicular to the direction of travel. They are transverse, not longitudinal.
• II. Sound waves in the air: Air particles vibrate back and forth along the direction the sound travels, producing compressions and rarefactions. They are longitudinal.
• III. Waves on a vibrating string: The string moves up and down (or side to side) while the wave travels along its length. They are transverse.

Step 4: Conclusion Only statement II is longitudinal.

Answer: B. II only

Exam tip: Remember that sound is the classic longitudinal wave. Light, radio waves, X-rays, string waves, and water waves are all transverse. When a question lists several waves, look for sound first. A quick memory aid: "Sound is Squeezing (compressions), so it is longitudinal."