Lecture Notes: Waves and Electromagnetic Spectrum

Understanding Waves

General Properties

• Waves transfer energy without transferring matter.
• Two main types: transverse waves and longitudinal waves.

Transverse Waves

• Direction of vibration is perpendicular to the direction of wave propagation.
• Examples: water waves, seismic secondary waves, Slinky waves, electromagnetic waves.
• Key terms:
  • Crest: Highest point of the wave.
  • Trough: Lowest point of the wave.

Longitudinal Waves

• Direction of vibration is parallel to the direction of wave propagation.
• Examples: sound waves, Slinky waves, seismic primary waves.
• Key terms:
  • Compression: Particles are close together.
  • Rarefaction: Particles are far apart.

Wave Parameters

• Amplitude (A): Distance from equilibrium to peak, related to energy.
• Wavelength (λ): Distance between consecutive peaks or identical points.
• Frequency (f): Number of vibrations per second, measured in Hertz (Hz).
• Period (T): Time for one wave cycle, T = 1/f.
• Speed (v): Distance traveled per unit time, v = λ * f.*

Wavefronts and Ripple Tanks

• Wavefronts: Lines along peaks or compressions.
• Ripple Tank: Demonstrates wave behaviors like reflection and refraction.

Reflection, Refraction, and Diffraction

Reflection

• Waves change direction upon hitting an obstacle, speed, and wavelength remain constant.
• Angle of incidence equals angle of reflection.

Refraction

• Waves bend when entering a different medium due to speed change, frequency remains constant.
• Snell’s Law: n₁ sin(θ₁) = n₂ sin(θ₂).

Diffraction

• Waves spread out when passing through a gap or around an obstacle.
• More diffraction when the gap size is similar to the wavelength.

Light Waves and Optics

Properties of Light

• Light is a transverse and electromagnetic wave.
• Speed: 3 × 10⁸ m/s in a vacuum.
• Exhibits reflection, refraction, and diffraction.

Reflection of Light

• Follows rules of reflection: angle of incidence equals angle of reflection.

Refraction of Light

• Light bends when moving through different mediums, speed changes but frequency remains constant.
• Refractive index (n): ratio of speed in vacuum to speed in medium.
• Critical angle and total internal reflection occur when light travels from a dense to less dense medium.

Lenses

• Converging Lens: Brings parallel rays to a focus; used in magnifying glasses.
• Diverging Lens: Spreads out parallel rays.
• Real Image: Formed when light rays meet.
• Virtual Image: Formed when light rays appear to meet.

Electromagnetic Spectrum

Overview

• Includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, gamma rays.
• All are transverse waves traveling at light speed in vacuum.

Uses and Risks

• Radio Waves: Communication, GPS.
• Microwaves: Cooking, communication.
• Infrared: Remote controls, thermal imaging.
• Visible Light: Vision, photography.
• Ultraviolet: Tanning, sterilization.
• X-rays: Medical imaging.
• Gamma Rays: Sterilization, cancer treatment.
• Risks: Higher frequency waves (UV, X-rays, gamma rays) are more ionizing and harmful.

Sound Waves

Properties

• Longitudinal waves requiring a medium.
• Travel faster in solids than liquids, and faster in liquids than gases.

Speed of Sound

• Approx. 330 m/s in air, varies with temperature.
• Speed measurement using echoes and timing methods.

Ultrasound

• High-frequency sound waves (>20,000 Hz).
• Uses: Sonar, medical imaging, cleaning, and detecting cracks.

Note: Candidates need to have a thorough understanding of the syllabus and the figure outlines provided in the course material.