How a wave carries energy through a medium without carrying the medium itself, why sound needs one to travel and light does not, and how to use the wave speed equation to find a missing frequency, wavelength, or speed on the HESI A2 physics subtest.
ObjectiveP.4.1Read4 minExam weightWaves, Sound and Light ≈ 20% of Physics
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You can tell a transverse wave apart from a longitudinal wave, and explain which kind sound is.
You can identify a wave's wavelength, frequency, and amplitude from a description or a diagram.
You can calculate a wave's speed, frequency, or wavelength when you are given the other two values.
What the lesson concludes
A wave carries energy through a medium, or for light, through empty space, without carrying the medium itself along with it.
A transverse wave displaces its medium at right angles to the direction of travel; a longitudinal wave displaces it back and forth along that same direction, as compressions and rarefactions.
Sound is a longitudinal wave and needs a medium, solid, liquid, or gas, to travel; unlike light, it cannot cross a vacuum.
Wave speed equals frequency times wavelength (v = frequency × wavelength), so at a fixed speed, a higher frequency always means a shorter wavelength.
Amplitude sets a wave's energy, not its speed. A louder sound has greater amplitude; a higher pitched sound has greater frequency.