Light and light waves

• infared waves

  infared (IR) waves are transverse waves. Their vibrations or oscillations are changes in electrical and magnetic fields at right angles to the direction of wave travel.

  All electromagnetic waves:

  • transfer energy as radiation from the source of the waves to an absorber
  • can travel through a vacuum such as in space
  • travel at the same speed through a vacuum or the air

  infared waves travel at 300,000,000 metres per second (m/s) through a vacuum.
• infared waves form a continuous spectrum of waves. This includes:

  • waves with a very short wavelength, high frequency and high energy
  • waves with a very long wavelength, low frequency and low energy

  infared waves can be separated into seven distinct groups in the spectrum.
• Each group contains a range of frequencies. For example, visible light contains the limited range of frequencies that can be detected by the human eye:

  • red light has the lowest frequencies of visible light
  • violet light has the highest frequencies of visible light
• Light travels in straight lines
• The path of light is called its ray
• Reflection occurs when light bounces back from a smooth surface
• Shadows- light can pass through some but not all materials. If something gets in the way of light, a shadow is formed
• Transparent materials- are materials that light can pass straight throught (transmitted)
• Translucent materials- allow light to be transmitted but they change some of the rays and re-emit the light in all directions
• Opaque materials- do not let any light through them at all
• two things that affect how shadows are formed: the closer the object is to the light source, the larger the shadow. Shadows are shorter if the light source is almost over head.
• The angle between the incident ray and normal line determines whether an image will form or not. The smaller the angle, the more likely it is that an image will form.
• The speed of light: unchanged medium of 300,000 km/s
• we see things when light enters our eyes
• The angle the ray is reflected is always the same as the angle the light hits the mirror, with both angles being measured from the normal.

  This is summarised by the law of reflection, which states: “the angle of reflection is equal to the angle of incidence”, or simply “i=r”.

  This law works for any angle. For example:
• This is summarised by the law of reflection, which states: “the angle of reflection is equal to the angle of incidence”, or simply “i=r”.

  A) angle incidence

  B) incident ray

  C) normal

  D) reflected ray

  E) angle reflection

  F) plane mirror

  G) 30

  
• When light travels through different materials, its speed changes. This means that the wavelength also changes because the frequency stays constant. When light passes into a material where the speed is less than c (such as glass), the wavelength decreases. If the speed increases (like air to vacuum), then the wavelength increases.
• refractionLight waves change speed when they pass across the boundary between two substances with a different density, such as air and glass. This causes them to change direction, an effect called refraction.
• • the light slows down going into a denser substance, and the ray bends towards the normal
  • the light speeds up going into a less dense substance, and the ray bends away from the normal.

  A) light

  B) air

  C) glass