Q: What does IP Combined Science Notes (Lower Sec, Year 1-2): 09) Waves, Light & Sound cover? A: Use wave speed equations, draw ray diagrams, and interpret sound investigations covering frequency and amplitude.
Wave behaviour explains ripples on water, colour from prisms, and the pitch of your voice. Work with both qualitative diagrams and quantitative calculations.
Learning targets
Define transverse and longitudinal waves with particle motion diagrams.
Apply v=fλ to calculate wave speed, frequency, or wavelength.
Draw ray diagrams for reflection, refraction, and dispersion.
Interpret sound intensity and frequency data, including oscilloscope traces.
1. Wave terminology
Term
Meaning
Amplitude
Maximum displacement from equilibrium.
Wavelength (λ)
Distance between successive crests/compressions.
Frequency (f)
Number of complete waves per second (Hz).
Period (T)
Time for one wave, T=f1.
Wave speed (v)
Distance travelled per second, v=fλ.
Transverse waves: particles oscillate perpendicular to wave direction (light, water surface). Longitudinal waves: particles oscillate parallel to wave direction (sound).
2. Wave calculations
Worked example - Ripple tank
Ripples have wavelength 1.5cm and frequency 12Hz.
v=fλ=12×1.5×10−2=0.18,m⋅s−1.
If wave speed remains constant and frequency doubles, wavelength halves.
Sound travel time
Speed of sound in air ≈340m⋅s−1. Lightning thunder delay of 4.5s implies distance:
d=vt=340×4.5=1.53×103,m.
3. Light behaviour
Reflection
Law of reflection: angle of incidence = angle of reflection. Use normal line for diagrams.
Refraction
When light enters denser medium (higher refractive index), it bends towards the normal; speed decreases.
Snell's law for extension: n1sinθ1=n2sinθ2.
Dispersion
Prism splits white light into spectrum because different wavelengths refract at slightly different angles.
Worked example - Glass block experiment
Light enters glass at θ1=35∘, refractive index n=1.52.
sinθ2=1.52sin35∘=0.376⇒θ2=22.1∘.
Draw emergent ray parallel to incident ray when exiting a rectangular block (due to symmetrical refraction).
4. Sound wave interpretation
Oscilloscope trace amplitude corresponds to loudness; frequency determines pitch.
Doubling amplitude doubles energy carried, approximate 6 dB increase.
Higher frequency waves have shorter periods: T=f1.
Worked example - Frequency from oscilloscope
If 4 divisions represent one full cycle and time-base setting is 2.0ms⋅div−1:
T=4×2.0×10−3=8.0×10−3,s.
f=T1=125,Hz.
Try it yourself
Sketch particle displacement diagrams comparing transverse and longitudinal waves.
A light ray passes from air into water at 50∘ to the normal. Refractive index of water =1.33. Calculate refracted angle and sketch the ray.
Two tuning forks produce beats at 4Hz. One fork has frequency 256Hz. Determine possible frequencies of the second fork and describe how to identify the higher one experimentally.
