light and electromagnetic waves

• electromagnetic spectrum

  • the frequency increase and the wave length decreases as the electromagnetic spectrum goes from radio to gamma rays

  
• radio waves are used for communication, radar and TV signals.
• microwaves are used for cooking food and satellite communications.
• infrared radiation is used by animals to detect heat and also used in remote controls.
• visible light is what we see with our eyes and can be split into different colours using a prism.
• ultraviolet radiation is used in tanning beds and sunbeds but it can cause skin cancer so people use fake tan instead.
• gamma rays are used in cancer treatment and nuclear power plants.
• x-rays are used in medical imaging such as x-ray machines and CT scans.
• Electromagnetic waves are a form of radiation that travel though the universe.
• Electromagnetic waves differ from mechanical waves in that they do not require a medium to propagate. This means that electromagnetic waves can travel not only through air and solid materials, but also through the vacuum of space.
• Exposure to low frequency fields that are strong enough can lead to dizziness, seeing light flashes and feeling tingling or pain through stimulation of nerves. Exposure to radiofrequency fields that are strong enough can lead to heating of body tissue, and result in damage to tissues and organs.
• they travel the same, at speed of 3 x 10^8m/s
• oscillation = vibration
• electromagnetic waves = A transverse wave caused by oscillations in an electromagnetic field.
• Electromagnetic (EM) waves are transverse waves. Their vibrations or oscillations are changes in electrical and magnetic fields at right angles to the direction of wave travel.
• Radio waves:

  • used for ommunication such as broadcasting tv and radio, communications and satellite transmissions.
  • They do not cause damage if absorbed by the human body, and they can be reflected to change their direction.
• list the electromagnetic spectrum in order

  radio, microwave, infrared, visible light, ultra violet, x ray, gamma rays
• microwave:

  • used for cooking food, communications and for satellite communications.
  • High frequency microwaves have frequencies which are easily absorbed by molecules in food.
  • The internal energy of the molecules increases when they absorb microwaves, which causes heating.
  • Microwaves pass easily through the atmosphere, so they can pass between stations on Earth and satellites in orbit.
• infrared :

  • used by electrical heaters, cookers for cooking food, short-range communications like remote controls, optical fibres, security systems and thermal imaging cameras which detect people in the dark. 
  • Infrared light has frequencies which are absorbed by some chemical bonds. The internal energy of the bonds increases when they absorb infrared light, which causes heating. 
• visible light :

  • used in photography and illumination. 
  • It is also used in fibre optic communications, where coded pulses of light travel through glass fibres from a source to a receiver.
• reflection of light :

  • angles of incidence and reflection are measured between the light ray and the normal
  • law of reflection states - angle of reflection = angle of incidence e.g. a light ray hits a surface at 25°, it will be reflected at 25°.
• specular reflection (reflection from smooth/flat surface) :

  • In a virtual image, the rays appear to diverge from behind the mirror, so the image appears to come from behind the mirror.
  • image is upright and virtual
• diffuse reflection :

  • if the surface is rough the light will be reflected but the rays will be scattered in all directions, may distort the image of the object being reflected
• refraction :

  • glass is denser than air so light slows down when entering glass
  • light ray speeds up as it passes from glass into air, and bends away from the normal by the same angle.
• total internal refraction :

  allows light to be contained and guided along very thin fibres. Usually made of glass, these are called optical fibres, some of the uses are :