4.3 Waves

• Terms used in waves: wavelength, period, amplitude, frequency and velocity
• The wave equation
• Real life effects of the properties of waves: reflection, refraction, diffraction
• Applications of the properties of waves in real life

• explain the terms used in waves
• interpret the wave equation as used in science
• calculate wave characteristics using the wave equation
• demonstrate the effects of the properties of waves in real life
• appreciate the applications of the properties of waves in real life

“How are waves applicable in our day-to-day life?”

“Why can you hear someone round a corner but not see them?”

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1. Describing a wave
   40 min · 1 practice tasks · quiz
   The five quantities that describe any wave, and the one equation linking them.
2. Reflection, refraction, diffraction and their uses
   40 min · 2 practice tasks · quiz
   Three things every wave does, and the technologies built on each.
3. Amplitude and the energy of a wave
   40 min · 1 practice tasks · quiz
   Amplitude is height from the rest line, and it is the quantity that carries the energy.
4. Wavelength in metres
   40 min · 1 practice tasks · quiz
   Wavelength is the distance between two successive identical points, and it varies hugely from radio to light.
5. Frequency, period and pitch
   40 min · 1 practice tasks · quiz
   Frequency is waves per second; period is seconds per wave; they are reciprocals.
6. Wave speed is set by the medium
   40 min · 1 practice tasks · quiz
   A wave's speed depends on what it travels through, not on how hard you shake the source.
7. Rearranging the wave equation
   40 min · 1 practice tasks · quiz
   v = fλ can be solved for any one of the three quantities, once units are consistent.
8. Worked examples with v = fλ
   40 min · 1 practice tasks · quiz
   Sound, water, ultrasound and radio all use the same equation, with different typical numbers.
9. Period first, then the wave equation
   40 min · 1 practice tasks · quiz
   When you are given the period, convert it to frequency before using v = fλ.
10. The ripple tank
    40 min · 1 practice tasks · quiz
    A shallow tray, a vibrator and a lamp let the class see wave properties as moving shadows.
11. Reflection of waves
    40 min · 1 practice tasks · quiz
    A wave bounces off a barrier with angle in equal to angle out; speed, frequency and wavelength stay the same.
12. Refraction of waves
    40 min · 1 practice tasks · quiz
    A wave changes speed when the medium changes; frequency stays the same, so wavelength and often direction change.
13. Diffraction at a gap
    40 min · 1 practice tasks · quiz
    Waves spread through a gap or around an obstacle, most when the gap is about one wavelength wide.
14. Why you hear round a corner but cannot see
    40 min · 1 practice tasks · quiz
    Sound diffracts at a doorway because its wavelength matches the gap; light does not, because its wavelength is tiny.
15. Ultrasound, scans and sonar
    40 min · 1 practice tasks · quiz
    High-frequency sound reflects from tissue and from the sea bed; the echo time gives distance.
16. Radio, KBC and phones
    40 min · 1 practice tasks · quiz
    Radio and phone signals are electromagnetic waves; wavelength decides aerial size and how well they go around hills.
17. Noise as pollution
    40 min · 1 practice tasks · quiz
    Unwanted sound of large amplitude damages hearing and rest; it can be reduced by distance, barriers and absorption.
18. Earthquake waves and waves at the coast
    40 min · 1 practice tasks · quiz
    Seismic waves carry earthquake energy; water waves slow and turn as they reach a Kenyan beach.