Physics Chapter 4: Waves, Oscillations, and Sound

Course Content

• The course covers Physics topics.
• Chapter 1: Physical Quantity, Units and Dimensions (1 week)
• Chapter 2: Motion in one Dimension (2 weeks)
• Chapter 3: Vector Analysis (2 weeks)
• Chapter 4: Waves, Oscillations and Sound (2 weeks)
• Chapter 5: Light, Lenses and Mirrors (2 weeks)
• Chapter 6: Heat and Thermodynamics (2 weeks)
• Chapter 7: Electricity & Magnetism (2 weeks)

Chapter 4: Waves, Oscillations, and Sound

• This chapter covers Waves, Oscillations, and Sound.
• It lasts for 2 weeks.

Periodic Motion Examples

• Disturbing water creates water waves.
• Disturbing air molecules makes sound waves.
• Disturbing electromagnetic fields causes electromagnetic waves (light).

Electromagnetic Waves

• Electromagnetic waves are subtle, with changing electrical and magnetic fields causing each other.
• A changing electric field creates a magnetic field.
• A changing magnetic field creates an electric field.
• This continuous cycle propagates the wave.
• Electromagnetic waves include light.

A Picture of Light

• Light is a transverse wave involving fluctuating electric and magnetic fields.
• These oscillating fields travel through space, affecting each location.

The Electromagnetic Spectrum

• Higher frequency means higher energy.
• All electromagnetic waves travel at the speed of light (approximated as 3 x 10⁸ m/s).
• Higher frequency light has shorter wavelengths.
• Radio waves are the lowest frequency (longest wavelength) and Gamma rays are the highest frequency (shortest wavelength).
• This spectrum includes radio waves, microwaves, infrared, visible light, ultraviolet, X-rays, and gamma rays.

Why Can't We See Infrared Light?

• Our eyes contain chemicals that trigger nerve impulses when struck by light.
• Our eyes evolved to perceive a specific range of frequencies as "visible light."
• Infrared light has lower frequencies than visible light and is therefore not perceived.

Danger of Ultraviolet, X-Ray, and Gamma Rays

• These are high-energy forms of radiation.
• They possess enough energy to break chemical bonds in cells (like DNA).
• Excessive exposure can damage cells; unrepaired damage leads to issues like cancer.

How do Microwave Ovens Work?

• Microwaves readily absorb water molecules.
• Microwaves in the oven bounce around until absorbed by water molecules.
• Wet substances heat up; dry substances don't heat up as much.

Does Red Light Have Less Energy Than Blue Light?

• Yes.
• Higher frequency light carries more energy.
• Blue light has a higher frequency than red light.

Simple Harmonic Motion (SHM)

• SHM can be modeled as a uniform circular motion projected onto a straight line.
• The equations governing SHM include: x(t) = A cos(wt + φ), dx/dt = -ωA sin(wt + φ), and d²x/dt² = -ω²x.

Simple Harmonic Motion Parameters

• Period (T) = 2π/ω
• Frequency (f) = 1/T = ω / 2π (in Hertz, Hz)
• Angular Frequency (ω) = 2π/T = 2πf (in radians/second, rad/s)
• Velocity (v) = -ωA sin(wt + φ)
• Acceleration (a) = -ω²A cos(wt + φ)

Example - The Pendulum

• The period of a pendulum (T) depends only on the length of the string (L) and acceleration due to gravity (g): T=2π√(L/g).

Mechanical Waves

• Mechanical waves require a source of disturbance, a medium, and a propagation mechanism.
• Transverse waves involve medium movement perpendicular to propagation.
• Longitudinal waves involve medium movement parallel to propagation

Sinusoidal Waves

• Sinusoidal wave equation: y(x, t) = A sin[2π(x/λ - vt)]
• k = 2π/λ, ω = 2π/T, and v = fλ.

Example - Sinusoidal Wave

• A sinusoidal wave traveling in positive x-direction has given amplitude, wavelength, and frequency.
• The wave number, period, angular frequency, and velocity of the wave are calculated.
• Maximum velocity and acceleration are HW (Homework).

Superposition of Waves - Interference

• Superposition of waves results in constructive or destructive interference depending on phase difference.
  • Constructive interference occurs when the phase difference is 0° resulting in amplitude increase.
  • Destructive interference occurs when phase difference is 180° resulting in amplitude decrease.
• The resultant wave has a form of 2A cos(ø/2) sin(kx-wt+ø/2).

Standing Waves and Resonance

• Standing waves are created by the interference of two waves traveling in opposite directions.
• Nodes and antinodes are points of zero and maximum displacement, respectively.
• The distance between adjacent antinodes/nodes is λ/2.

Resonance in Air Columns

• Resonances in air columns with open or closed ends create harmonics (multiple frequencies) at certain wavelengths.
  • Open at both ends: Harmonics are multiples of fundamental (n=1,2,3...).
  • Closed at one end: Harmonics are odd multiples of fundamental (n=1,3,5...).

Example - Pipe Resonances

• A pipe open/closed at both ends and one closed end demonstrates fundamental vs. harmonic frequencies.

Calculate Harmonic Frequency

• The calculated frequency for a closed-end air column.

Sound Waves

• Sound waves are periodic motion resulting in displacement changes, and thus pressure.
• Sound intensity (I) is power per unit area (W/m²).
  • I= ΔP²/ 2pv

Example, Sound Intensity Limits

• The example provides calculation of pressure amplitude, and displacement amplitude associated with sound intensity (hearing and pain thresholds) at a given frequency.

Sound Level in Decibels (dB)

• A logarithmic scale (dB) compresses the wide range of sound intensities.
• Formula β = 10 log(I/I₀) describes the compression. (I₀ is threshold of hearing)

This quiz focuses on Chapter 4 of the Physics course, which covers Waves, Oscillations, and Sound. It explores the fundamental concepts and examples of wave motion, including electromagnetic waves and their characteristics. Test your understanding of these important physics principles.