Revise Electromagnetic spectrum for Cambridge 9702 (7.4)

Every electromagnetic wave shares a few core characteristics. Firstly, they are all transverse waves, meaning their oscillations are perpendicular to the direction they travel. Unlike sound waves, EM waves don't need a medium; they can travel through the vacuum of space. Most importantly, all EM waves travel at the same incredible speed in a vacuum.

$c = f\lambda$

Where $c$ is the speed of light in a vacuum ($3.00 x 10⁸ m s^{-1}$), $f$ is the frequency of the wave, and λ (lambda) is its wavelength. This fundamental relationship means that as the wavelength gets shorter, the frequency must increase to maintain a constant speed.

The electromagnetic spectrum is an ordered arrangement of these waves by their wavelength and frequency. Moving from the longest wavelengths (and lowest frequencies) to the shortest (and highest frequencies), the order is: Radiowaves, Microwaves, Infrared, Visible Light, Ultraviolet, X-Rays, and Gamma Rays. Each region has unique uses and properties due to its energy level, which is directly proportional to its frequency.

Each part of the electromagnetic spectrum is defined by a specific range of wavelengths and frequencies, which in turn dictates its properties and applications. Understanding these distinctions is crucial for applying physics concepts to real-world technology and interpreting astronomical observations.

Here is a breakdown of the principal components, their approximate wavelengths, and common uses:

• Radiowaves: Wavelengths > 10 cm. They have the lowest energy and are used for broadcasting radio and television signals, as well as in radio astronomy.
• Microwaves: Wavelengths from 1 mm to 30 cm. These are used in microwave ovens to heat food, for satellite communication, mobile phone networks, and radar systems.
• Infrared (IR): Wavelengths from 700 nm to 1 mm. Emitted by all objects with thermal energy, it is used in thermal imaging cameras, remote controls, and for data transmission in optical fibres.
• Visible Light: A narrow band with wavelengths from approximately 400 nm (violet) to 700 nm (red). This is the only portion of the spectrum that the human eye can detect.
• Ultraviolet (UV): Wavelengths from 10 nm to 400 nm. It has enough energy to cause chemical reactions, such as tanning and sunburn, and is used for sterilising equipment and in security marking.
• X-rays: Wavelengths from 0.01 nm to 10 nm. Their high energy and penetrating ability make them ideal for medical imaging (radiographs) and airport security scanners.
• Gamma Rays: Wavelengths < 0.01 nm. These are the most energetic and penetrating waves, produced by nuclear reactions. They are used in radiotherapy to destroy cancer cells and to sterilise medical instruments.

One key feature that distinguishes EM waves as transverse waves is their ability to be polarised. Polarisation involves restricting the oscillations of the wave to a single plane. Imagine shaking a rope through a picket fence; only the shakes parallel to the fence gaps can pass through. This phenomenon is direct evidence that EM waves are not longitudinal, but rather vibrate perpendicular to their direction of travel.