# Electromagnetic Waves & Electromagnetic Spectrum

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## Electromagnetic Waves

In terms of classical wave theory, a very hot object such as any star or sun produces a range of electromagnetic waves. (E.g. The Sun produces ultraviolet light in addition to visible light) Electromagnetic waves are often collectively referred to as electromagnetic radiation.

Electromagnetic radiation is produced by acceleration or sudden movement of electrons. The electron in motion constitutes the electric current that generates the magnetic field in the wave.

• Electromagnetic waves are transverse waves, consisting of electric and magnetic waves at right angles to each other and perpendicular to the direction of wave propagation.
• Electromagnetic waves can travel through vacuum and do not need a medium to traverse. They can travel through solids, liquids and gases.
• All electromagnetic waves have the same speed in vacuum of 3 x 108 m s-1 (commonly referred to as the ‘speed of light’). But the speed slows down in other material media.

## Electromagnetic Spectrum

The electromagnetic spectrum encompasses a vast range of radiation types, each with unique properties and applications, distinguished by their frequency and wavelength. This spectrum is continuous due to the myriad of oscillators present in any material, which can emit radiation across all frequencies.

### Gamma Rays

Gamma rays are the most energetic forms of electromagnetic radiation, with frequencies above $10^{19}$ Hz and wavelengths less than $10^{-11}$ meters. They possess the ability to penetrate most materials easily, making them useful in medical imaging and treatments, as well as in industrial applications for material inspection. Gamma rays are typically produced by nuclear reactions, such as those occurring in radioactive decay or in nuclear explosions.

Hint: To convert between frequencies and wavelengths, employ the wave velocity formula $v = f \lambda$, where $v$ represents the wave’s speed. In the context of gamma rays traveling through a vacuum, this speed aligns with the speed of light, approximately $3 \times 10^8$ meters per second, offering a precise benchmark for conversions.

Applications: Applications Of Gamma Rays

### X-Rays

Directly following gamma rays in energy, X-rays have frequencies ranging from $10^{17}$ to $10^{19}$ Hz and wavelengths between $10^{-11}$ to $10^{-8}$ meters. They are known for their ability to pass through soft tissue but are absorbed by denser materials like bone, which is why they are extensively used in medical imaging. X-rays are produced by X-ray tubes, which involve accelerating electrons to high energies before colliding them with a metal target.

Applications: Applications Of X-Rays

### Example 2: Wave Behavior in Different Mediums

Explain why electromagnetic waves can travel through the vacuum of space, but sound waves cannot.

Electromagnetic waves, such as light and radio waves, can travel through the vacuum of space because they do not require a medium to propagate. They consist of oscillating electric and magnetic fields that support each other as they travel through space. On the other hand, sound waves are mechanical waves that require a medium (solid, liquid, or gas) to travel through, as they propagate through the vibrations of particles in the medium. In the vacuum of space, where there are no particles to vibrate, sound waves cannot travel.

### Example 3: Safety and Electromagnetic Radiation

Considering the electromagnetic spectrum, why is it safe to be exposed to radio waves and infrared radiation but not to UV radiation or X-rays for extended periods?