Light Waves and Sound Waves

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Light Waves

  • Luminous objects, such as the Sun, give out light. Non-luminous objects only reflect light.
  • Light Waves are all Transverse waves.


  • The Angle of Incidence=The Angle of Reflection
  • This happens when light is bounced of a Plane Mirror

Images created by a Plane Mirror

  • Virtual Images look like they are behind a surface of a mirror so they are rays of light that do not pass through.
  • Real Images are produced when light passes through them. If you can produce a image on a screen, it is real.

Properties of an image in a Plane Mirror

  • The image is the same size as the object
  • The image is virtual as it cannot be produced on a screen.
  • The image is Laterally Inverted
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Light Waves (Continued)


  • When a ray of light travels from air to water it slows down as it crosses the boundrary between two different media.
  • The change in speed may cause the ray to change direction.
  • It refracts towards the normal as it slows down when it enters the the glass block.

Refractive Index

  • A ratio between the Angle of Incidence and Angle of Refraction.
  • Formula: n=sin(i) / sin(r)

Total internal reflection

  • When a ray of light passes from glass into air-The light is refracted away from the normal but there is a small amount of light that is also reflected from the glass.
  • When the angle of incidence increases and there is the critical angle which stops light from going through the glass and it is at 90 degrees the reflacted ray but still is weakly reflected ray.
  • When the angle of incidence is  further increased, the ray doesn't go through the glass but has a more stronger reflected ray as it is more dense as the refracted ray is not there. This is undergone total internal reflection
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Light Waves (Continued-2)

Formula for Critical Angle: sin(c)= 1 / n

Optical Fibres Use Total Internal Reflection

  • In a optical fibre, light undergoes total internal reflection as the outer coat gives lower reflactive index which means the reflacted ray is not there as the fibre is so narrow that light signals passing through it always hits the outer coats boundary at angles higher than a critical angle.
  • That's why it Fibres are used for Total Internal Reflection.
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Sound Waves

Sound Waves

  • Sound Waves are longitudinal waves.
  • When sound is made with the help of vibrations , it pushes air molecules closer together creating compression. And before compression the air molecules spread out spread out. This is called rarefraction.
  • An Oscilloscope can display sound waves as they sound waves into electrical signals which gives a trace on the screen if the sounds are high pitched, low-pitched, loud or quiet.
  • The greater the amplitude of the wave/vibration, the more energy it carries meaning it'll be loud.

The Higher the Frequency, the Higher the Pitch

  • Frequency is the number of complete vibrations each second.
  • Higher Frequency & Higher-pitched is a squeaking mouse.

You can use an Oscillscope to measure the Speed of Sound

You need 2 microphones, a ruler and a speaker.

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Analogue and Digital Signals

  • Information is converted into electrical signals before it is transmitted.
  • Analogue signals vary as they take any value within a certain range. The amplitude and frequency can vary continuously.
  • Digital can only take two values. These values tend to be on/off.

Digital Signals have Advantages Over Analogue

  • Both Ditgital and Analogue signals weaken as they travel, so they need to be amplified along the route. They pick up interference or noise from electical disturbance or other signals.
  • When an Analogue is amplified, the signal loses quality but for Digital it is ignored.
  • It is easier to transmit multiple signals at  the same time with one cable or EM wave(multiplexing) for Digital signals. If Analogue signals are of similar frequency it cause interference when it loses quality but with Digital it's much easier to tell them apart which means more information
  • Quantisation is the process of "rounding" multiple values in a smaller set so more information. Because of Ditigal has two values, it doesn't lose much info but for analogue the info is lost.
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