Electromagnetic (EM) Waves (AQA GCSE Physics): Revision Notes

6.2.1 Electromagnetic (EM) Waves

Electromagnetic Waves

Visible Light

• If we pass white light through a prism, it splits into a spectrum.
• Each colour of light has a different wavelength and frequency.
• Visible light is the only part of the electromagnetic spectrum that can be detected by the human eye.

Spectrum Order (from lower frequency, longer wavelength to higher frequency, shorter wavelength)

• Red
• Orange
• Yellow
• Green
• Blue
• Indigo
• Violet

Characteristics

• Lower frequency, longer wavelength (Red) to higher frequency, shorter wavelength (Violet).
• The electromagnetic spectrum is a continuous spectrum.
• They do not need a medium to travel in. All EM waves travel through a vacuum at 3 × 10⁸ m/s.

Mnemonic for Spectrum Order

Uses of Electromagnetic (EM) Waves

Radio Waves

• Transmission of Radio and Terrestrial TV Signals
  • Can travel long distances before being absorbed by buildings and trees.
  • Longer radio waves can spread out between hills due to diffraction.
  • Reflect off charged particles in the ionosphere, allowing them to travel long distances around the Earth.

Microwaves

• Heating Food
  • Water molecules in food absorb the energy of microwaves, causing the temperature of the food to increase.
• Communication with Satellites in Space
  • Microwaves can pass through the Earth's atmosphere without being refracted or reflected.

Infrared

• Emitted by Electrical Heaters and Cooking Food
  • The energy of infrared is easily absorbed by the surface of objects.
• Infrared Cameras
  • Used to check buildings for heat losses.

Visible Light

• Communication Using Fibre Optics
  • Optical fibres are thin strands of glass that transmit pulses of light to carry information.
• Carrying Telephone and Cable TV Signals
  • Short wavelengths allow it to carry a large amount of information.

Ultraviolet

• Energy Efficient Light Bulbs
  • Ultraviolet light is created inside the bulb and converted to visible light by the bulb's internal surface.
  • More energy-efficient due to the shorter wavelength of ultraviolet light.
• Sun Tanning

X-Rays and Gamma Rays

• Medical Imaging
  • X-rays: Visualise broken bones.
  • Gamma Rays: Detect cancer.
  • Both are very penetrating and can pass through body tissues.
  • X-rays are absorbed by bones, making them visible on X-ray images.
• Cancer Treatment
  • Both X-rays and Gamma Rays can be used to treat cancer.

Electromagnetic Waves

Need to learn the main groups, and in which order (for increasing wavelength or frequency).

• These are transverse waves.
• Do not need particles to move.
• In space, all waves have the same velocity (speed of light).
• They can transfer energy from a source to an absorber.
  • Microwave source to food.
  • Sun emits energy to Earth.

Relationships

• As speed is constant for all EM waves.
• As the wavelength decreases, the frequency must increase.
• As frequency increases, the energy of the wave increases.

Eyes

• Our retina can only detect visible light, a small part of the entire EM spectrum.
• This visible light is still an EM wave like X-rays and microwaves, do not forget!