Physics - Sound and Light

Physics - Sound and Light

1. Sound

   • Sound waves are longitudinal waves that must pass through a medium.
     • Echoes are reflections of sounds.
     • Their vibrations occur in the same direction as the direction of travel.
     • Sound waves can only travel through a solid, liquid or gas.
   • Vibrations
     • When an object or substance vibrates, it produces sound.
       • the greater the amplitude, the louder the sound. The greater the frequency, the higher the pitch.
   • Oscilloscopes of 3 sounds
     • Sounds 1 & 2
       • The sound waves have the same frequency, so the sounds have the same pitch.
       • Sound 2 has a greater amplitude than sound 1, so sound 2 is louder.
     • Sounds 2 & 3
       • The sound waves have the same amplitude, so the sounds have the same loudness.
       • Sound 3 has a greater frequency than sound 2, so sound 3 is higher pitched.
   • The range of human hearing.
     • Is between about 20 Hz and 20 kHz, but the range becomes less as we get older.
     • Sounds with frequencies above about 20 kHz are called ultrasound.

2. The Electromagnetic Spectrum

   • The electromagnetic spectrum is a continuous range of wavelengths. The types of radiation that occur in different parts of the spectrum have different uses and dangers, which depend on their wavelength and frequency.
   • White light can be split up using a prism to form a spectrum. The light waves are refracted as they enter and leave the prism. The shorter the wavelength of the light, the more it is refracted. As a result, red light is refracted the least and violet light is refracted the most, causing the coloured light to spread out to form a spectrum.
     • Visible light is just one type of electromagnetic radiation. There are various types of electromagnetic radiation, some with longer wavelengths than visible light and some with shorter wavelengths than visible light.
   • Electromagnetic waves form a continuous spectrum.
     • Radio waves have the lowest energy and frequency yet the longest wavelength. They are typically used for television signals
     • Microwaves are generally used for cooking and for the use of mobile phones
     • Infrared waves are most typically used for optical fibre communication
     • Visible light is generally used for seeing.
     • Ultraviolet waves are today used to detect forged bank notes
     • X-rays provide us with an ok resolution in medical images of our bones.
     • Gamma radiation has the highest energy and frequency yet the shortest wavelength. They are typicaly used today for killing cancer cells
   • The wavelengths vary across the electromagnetic spectrum from about 10–15 m to more than 104 m.

3. Communicating with Radio waves, Microwaves, Visible Light and Infrared.

   • Microwaves- Electromagnetic radiation with a frequency between that of visible light and radio waves.
   • Radiowaves
     • Used to transmit television and radio programes. Television uses higher frequencies than radio
     • Diffraction allows low frequency radio waves to be recieved behind hills, although repeater stations are often used to imporve the quality of the signals
     • The lowest frequency radio waves are also reflected from and electrically charged layer of the upper atmosphere, called the iononsphere.
   • Microwaves
     • Microwave radiation is also used to transmit signals but this time from mobile phones
     • Microwave transmitters and receivers on buildings and masts communicate with the mobile telephones in their range.
     • Using a mobile phone is not harmful as the intensity of the microwaves is too low to damge the tissues by heating and microwaves are not ionising
   • Visible Light
     • It allows us to communicate with one another through books, hand signals and video
     • The use of visible light needs the transmitter and receiver to be in the line of sight.
     • Cameras let us record still pictures and movies, and photography is a main use of visible light.
     • Very bright light can damage our eyes – you should never look directly into the Sun.
   • Infrared Radiation
     • We cannot see infrared radiation, but we can feel it as heat energy
     • High intensity infrared is used in heaters, toasters and grills, and it can cause burns.
     • Infrared sensors can detect heat from the body. They are used insecurity lights and burglar alarms
     • Infrared radiation is also used to transmit information from place to place, including remote controls for the TV and DVD players

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