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Types of Waves
Some basic definitions:
Wave - A periodic disturbance that transfers energy
Medium - The matter through which the wave travels
Not all waves actually require a physical medium to travel through. This fact allows us to place all waves into two types:
Mechanical waves - The first type: waves that need a physical medium to travel through. Example - sound waves. Sound waves cannot travel through a vacuum.
Electromagnetic waves - The second type: do not need a physical medium to propagate through. Electromagnetic waves can travel through a vacuum. Examples: radio waves, visible light, X-rays, etc.
1. Mechanical Waves
When a mechanical wave moves through a physical medium, the particles in the medium oscillate with simple harmonic motion.
Simple harmonic motion
The blue ball above is in simple harmonic motion. Imagine this ball represents a particle in a solid material. If this particle is connected to other nearby particles, its motion will affect the motion of surrounding particles.
Transverse wave
In the diagram above, the motion of the leftmost particle causes the adjacent particle to oscillate. This oscillation is passed down through the entire chain of particles. Note that the particles vibrate up and down (vertically), while the wave itself moves from left to right (horizontally). This specific type of wave motion is called a transverse wave.
Transverse wave - A wave in which the particles of the medium move perpendicular to the direction of wave motion.
Waves can also move through a material when the particles of the medium vibrate back and forth in the direction of wave motion. This type of wave is called a longitudinal wave.
Longitudinal waves - A wave in which the particles of the medium move parallel to the direction of wave motion.
Longitudinal waves
In the longitudinal wave above, the leftmost particle vibrates horizontally with simple harmonic motion, causing the particles to its right to also vibrate with simple harmonic motion. The wave energy is transferred horizontally to the right.
Mechanical transverse waves can only move through solids, while longitudinal waves can move through solids, liquids, and gases.
Surface waves: Longitudinal waves originate in the depths of oceans, while water particles on the surface follow a circular path, sometimes parallel to the wave motion and sometimes perpendicular to the wave motion.
2. Electromagnetic Waves
Electromagnetic waves are waves that propagate through space and consist of two perpendicular fields:
- Electric field
\[(E)\]
- Magnetic field
\[(B)\]
Basic equations:
Maxwell's equations:
\[∇·E =\frac{ ρ}{ε₀}\]
\[ ∇×E =\frac { -∂B}{∂t }\]
\[∇·B = 0 \]
\[ ∇×B = μ_₀J + μ_₀ε_₀\frac {∂E}{∂t}\]
Electromagnetic wave equation:
\[∇²E = μ_₀ε_₀ \frac {∂²E}{∂t²} \]
\[∇²B = μ_₀ε_₀ \frac {∂²B}{∂t²}\]
Wave speed (speed of light):
\[ c = \frac {1}{√(μ₀ε₀)} ≈ 3×10⁸ m/s\]
Electromagnetic spectrum:
- Radio waves (longest wavelength)
- Microwaves
- Infrared
- Visible light (400-700 nm)
- Ultraviolet
- X-rays
- Gamma rays (shortest wavelength)
Important properties:
Speed (c) = Frequency (f) × Wavelength (λ)
(Photon energy)
\[E = hf \]
Wave speed in any medium
\[c = 1/√(μϵ) \]
Practical applications:
- Wireless communications
- Medical imaging (X-rays and MRI)
- Radar systems
- Optical fibers
This is a simple animation representing an electromagnetic wave. The blue vectors show the oscillation of the electric field, and the yellow vectors show the oscillation of the magnetic field.
Types of Waves |
Some basic definitions:
Medium - The matter through which the wave travels
Not all waves actually require a physical medium to travel through. This fact allows us to place all waves into two types:
Mechanical waves - The first type: waves that need a physical medium to travel through. Example - sound waves. Sound waves cannot travel through a vacuum.
Electromagnetic waves - The second type: do not need a physical medium to propagate through. Electromagnetic waves can travel through a vacuum. Examples: radio waves, visible light, X-rays, etc.
1. Mechanical Waves
When a mechanical wave moves through a physical medium, the particles in the medium oscillate with simple harmonic motion.Simple harmonic motion
The blue ball above is in simple harmonic motion. Imagine this ball represents a particle in a solid material. If this particle is connected to other nearby particles, its motion will affect the motion of surrounding particles.
Transverse wave
In the diagram above, the motion of the leftmost particle causes the adjacent particle to oscillate. This oscillation is passed down through the entire chain of particles. Note that the particles vibrate up and down (vertically), while the wave itself moves from left to right (horizontally). This specific type of wave motion is called a transverse wave.
Transverse wave - A wave in which the particles of the medium move perpendicular to the direction of wave motion.
Waves can also move through a material when the particles of the medium vibrate back and forth in the direction of wave motion. This type of wave is called a longitudinal wave.
Longitudinal waves - A wave in which the particles of the medium move parallel to the direction of wave motion.
Longitudinal waves
In the longitudinal wave above, the leftmost particle vibrates horizontally with simple harmonic motion, causing the particles to its right to also vibrate with simple harmonic motion. The wave energy is transferred horizontally to the right.
Mechanical transverse waves can only move through solids, while longitudinal waves can move through solids, liquids, and gases.
Surface waves: Longitudinal waves originate in the depths of oceans, while water particles on the surface follow a circular path, sometimes parallel to the wave motion and sometimes perpendicular to the wave motion.
2. Electromagnetic Waves
Electromagnetic waves are waves that propagate through space and consist of two perpendicular fields:
- Electric field \[(E)\]
- Magnetic field \[(B)\]
Basic equations:
Maxwell's equations:
\[∇·E =\frac{ ρ}{ε₀}\] \[ ∇×E =\frac { -∂B}{∂t }\] \[∇·B = 0 \] \[ ∇×B = μ_₀J + μ_₀ε_₀\frac {∂E}{∂t}\]Electromagnetic wave equation:
\[∇²E = μ_₀ε_₀ \frac {∂²E}{∂t²} \] \[∇²B = μ_₀ε_₀ \frac {∂²B}{∂t²}\]Wave speed (speed of light):
\[ c = \frac {1}{√(μ₀ε₀)} ≈ 3×10⁸ m/s\]Electromagnetic spectrum:
- Radio waves (longest wavelength)
- Microwaves
- Infrared
- Visible light (400-700 nm)
- Ultraviolet
- X-rays
- Gamma rays (shortest wavelength)
Important properties:
Speed (c) = Frequency (f) × Wavelength (λ)(Photon energy) \[E = hf \] Wave speed in any medium \[c = 1/√(μϵ) \]
Practical applications:
- Wireless communications
- Medical imaging (X-rays and MRI)
- Radar systems
- Optical fibers
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