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Waves: Energy on the Move
A wave carries energy, not matter: a leaf on a pond only bobs while ripples spread. This is why exam questions classify waves first.
In a transverse wave the particles vibrate at right angles to the direction the wave travels. The wave is made of crests and troughs. Waves on a stretched string and all electromagnetic waves, including light, are transverse.
In a longitudinal wave the particles vibrate along the direction of travel, creating compressions (squeezed regions) and rarefactions (stretched regions). Sound in air is the standard example; so are waves in a spring pushed back and forth.
A second split matters just as much. Mechanical waves, such as sound and string waves, need a material medium. Electromagnetic waves need none, which is why sunlight reaches us through empty space but a bell rung in a vacuum jar is silent.
Worked example: a cork on water moves up and down while the ripple moves sideways. Particle motion is perpendicular to wave motion, so the ripple is treated as transverse in school physics.
1. Which of the following is a longitudinal wave?
2. A source of frequency 50 Hz produces sound of wavelength 6.8 m. What is the speed of the sound?
3. Two tuning forks of frequencies 256 Hz and 260 Hz are sounded together. How many beats are heard per second?
4. The loudness of a sound mainly depends on its:
5. In which of the following does sound travel fastest?
6. A train sounding its whistle approaches a stationary listener. The listener hears:
7. A wave's frequency stays the same while its speed doubles on entering a new medium. Its wavelength will:
8. Which statement about waves is correct?