This guide covers the fundamental concepts of mechanical, electromagnetic, and sound waves. Understanding the properties and key formulas in this chapter is essential for your O/L Physics questions.

1. Introduction to Waves

Short Notes & Key Concepts

• What is a Wave? A disturbance that travels through a medium or space, transferring energy from one point to another without transferring matter.

• Two Main Categories:

  1. Mechanical Waves: Require a material medium (solid, liquid, or gas) to travel. Examples: Sound waves, water waves, waves on a rope.

  2. Electromagnetic (EM) Waves: Do not require a medium to travel; they can travel through a vacuum. Examples: Light, radio waves, X-rays.

2. Types of Mechanical Waves

3. Key Wave Quantities & The Wave Equation

• Amplitude (A): The maximum displacement of a particle from its rest or equilibrium position. It relates to the energy of the wave.

• Wavelength (λ): The distance between two consecutive identical points on a wave (e.g., from one crest to the next crest). Measured in meters (m).

• Frequency (f): The number of complete waves (or oscillations) that pass a point per second. Measured in Hertz (Hz).

• Period (T): The time taken for one complete wave to pass a point. It's the inverse of frequency. Measured in seconds (s).

  • Formula: f = 1 / T

• Speed (v): How fast the wave travels. Measured in meters per second (m s⁻¹).

• The Wave Equation (VERY IMPORTANT!): This connects speed, frequency, and wavelength. Speed = Frequency × Wavelength v = fλ

4. Electromagnetic (EM) Spectrum

• EM waves are transverse waves that travel at the speed of light (3 × 10⁸ m s⁻¹) in a vacuum.

• They are arranged by frequency/wavelength in the EM Spectrum.Low Frequency / Long Wavelength → High Frequency / Short Wavelength Radio waves → Microwaves → Infrared → Visible Light → Ultraviolet → X-rays → Gamma rays

  • Mnemonic to remember the order: "Rich Men In Vegas Use Xpensive Gadgets"

5. Sound Waves

• Sound is a longitudinal mechanical wave. It needs a medium to travel and cannot travel through a vacuum.

• Sound travels fastest in solids, slower in liquids, and slowest in gases.

• Characteristics of Sound:

  • Pitch: How high or low a sound is. It depends on the frequency.

    • High Frequency = High Pitch (e.g., a whistle)

    • Low Frequency = Low Pitch (e.g., a drum)

  • Loudness: The intensity of the sound. It depends on the amplitude.

    • High Amplitude = Loud Sound

    • Low Amplitude = Soft Sound

  • Quality (or Timbre): The property that allows you to distinguish between two sounds of the same pitch and loudness (e.g., a piano vs. a violin playing the same note). It depends on the waveform.

• Hearing Range:

  • Human Audible Range: 20 Hz to 20,000 Hz.

  • Infrasound: Frequencies below 20 Hz.

  • Ultrasound: Frequencies above 20,000 Hz.

• Uses of Ultrasound: Because it's high frequency, it can be used for imaging.

  • SONAR: Used in ships to measure sea depth and locate fish.

  • Medical Scanning: To safely view internal organs, like a fetus in the womb.

Exam Tips & Tricks

1. Transverse vs. Longitudinal: This is a classic comparison question. Know the definitions, diagrams (crest/trough vs. compression/rarefaction), and one example for each.

2. Master the Wave Equation v = fλ: You will almost certainly get a calculation question using this formula. Practice rearranging it to find f (f = v/λ) or λ (λ = v/f).

3. Sound Characteristics: This is a guaranteed topic. You MUST know the link: Pitch ↔ Frequency, Loudness ↔ Amplitude, Quality ↔ Waveform.

4. Sound Needs a Medium: Be able to describe the "bell in a vacuum jar" experiment to prove that sound cannot travel in a vacuum.

5. EM Spectrum Order: Use the mnemonic to memorize the order of the EM waves. Questions often ask you to arrange them or identify which has a higher/lower frequency.