Waves
9th Grade Science · 8 lessons
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Lessons in this unit
- 1Transverse and Longitudinal WavesIn a transverse wave the oscillation is perpendicular to the direction of travel — light and water ripples. In a longitudinal wave it is parallel, producing compressions and rarefactions — sound is the everyday example.Experiment
- 2Wave Speed, Frequency and WavelengthThe wave equation links them all: v = fλ. Frequency is oscillations per second in hertz, wavelength is the distance between matching points, and speed is set mainly by the medium. Change frequency in a fixed medium and wavelength changes to compensate.Experiment
- 3Reflection, Refraction and DiffractionWaves reflect off barriers with the angle of incidence equal to the angle of reflection. They refract — change direction — when their speed changes at a boundary. They diffract, spreading out, when they pass through a gap comparable to their wavelength.Experiment
- 4Amplitude, Intensity and EnergyAmplitude is the maximum displacement from rest. The energy a wave carries goes with amplitude squared, so doubling the amplitude of a sound quadruples its energy — but our ears perceive loudness roughly logarithmically, which is why decibels are used.Experiment
- 5The Electromagnetic SpectrumAll electromagnetic waves are transverse and travel at 3 × 10⁸ m/s in a vacuum. From radio through microwave, infrared, visible, ultraviolet and X-ray to gamma, frequency and photon energy rise while wavelength falls — and so does the hazard.Lesson
- 6Total Internal Reflection and Optical FibresWhen light travels from a denser to a less dense medium beyond the critical angle, it reflects entirely back inside. Optical fibres exploit this to carry light for kilometres with almost no loss, which is what carries most internet traffic.Experiment
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