Uses of EM (Edexcel GCSE Physics Combined Science): Revision Notes

Uses of EM

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. Visible light is the type of light we can see, so we can use it to illuminate things and capture images.

• Photographic Film:

  • Traditional cameras use photographic film that reacts to light to form an image.

• Digital Cameras:

  • Digital cameras have image sensors that detect visible light and convert it into an electrical signal.
  • This signal is then used to store the image digitally or print it.

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
• Ultraviolet (UV) Light in Fluorescent Lamps
• Fluorescence occurs when certain chemicals absorb ultraviolet radiation and re-emit it as visible light. This is why fluorescent lamps appear so bright.
• Uses of Fluorescent Lamps:
  • They use UV light to emit visible light.
  • Fluorescent lamps are energy-efficient, making them ideal for long-term lighting.

X-Rays and Gamma Rays

Gamma Rays for Sterilisation

• Medical Sterilisation: Gamma rays are used to sterilise medical instruments by killing bacteria and microbes.
• Food Sterilisation: Gamma radiation sterilises food, allowing it to stay fresh longer without freezing.
• Cancer Treatments: Gamma rays are targeted at cancer cells to destroy them. Care must be taken not to damage healthy cells.

X-Rays for Imaging

X-rays allow us to see inside objects, including the human body. They pass through soft tissue but are absorbed by denser materials like bones and metals.

Uses of X-Rays:

• Medical Imaging: X-rays are used by radiographers in hospitals to help doctors diagnose broken bones.
• Airport Security: X-ray scanners detect hidden objects that can't be found with metal detectors. How X-ray Images Are Produced:

1. X-ray radiation is directed through the body or object onto a detector plate.
2. Denser materials, like bones, absorb X-rays and appear as brighter areas on the image, creating a contrast that forms the picture.

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!