Physics 1 Topic 2

Physics 1 Topic 2

1. Electromagnetic waves

   • Radiowaves
     • Radio waves are mainly used for communications to broadcast TV and radio as it transmits satellite signals in the same way as microwaves
       • Long wave radio
         • Wavelengths of 1-10KM as it could be transmitted for e.g London and be then transmitted half way across the world
           • This is because the wavelengths bend around curved surfaces such as hills and tunnels and the signal will still be recieved
       • Short wave radio
         • Wavelengths of 10-100m and can be received from far distances from the transmitter
           • This is because they are transmitted into the ionosphere which is an electrically charged layer of the Earth's upper mantle
             • Medium wave signals can also reflect through the ionosphere depending on the conditions and the time of day
   • Microwaves
     • The dangers is that they all have a similar frequency which causes the molecules to vibrate resulting in heating
       • Handset on mobile phones could cause brain tumours although it hasn't been discovered yet
     • Used for satellite and mobile phones
       • The waves are easily passed through the earth's watery atmosphere and the signal from the transmitter is transmitted into space where it is picked up by the satellite dish receiver orbiting thousands of kilometres above Earth
         • The satellite dish receives the signal back onto the ground although there is a time delay as it takes time in order for the signal to travel the long distance
           • Microwave ovens use different wavelengths as the microwaves absorb the water molecules from food and gives out thermal energy
             • The microwaves penetrate a few centimetres from the food before absorbing the water molecules from the food and the energy is conducted to other parts of the food
   • Visible light
     • We need visible light in order to see
       • Light enters your eye as it gets refracted through the lens and focused onto the retina of the eye it sends out messages to the brain and the brain then interprets them
   • Ultra violet
     • Discovered by Ritter soon after 1801
       • He wanted to see if there was another side beyond violet
         • He knew that silver chloride turned from white to black when exposed to light so he decided to measure how quickly silver chloride strips changed when exposed to light to different colours of light
           • He created a spectrum of using a light source and a prism and exposed the strips to each colour
             • He then timed how long it took for the strips to turn black
               • The quickest when exposed to light was nearer the blue end of the spectrum
                 • Finally he placed a strip just past the violet area and saw that there was a quickest change and discovered that ultraviolet radiation is an invisible form of light
     • UV has more energy and an even more higher frequency than Infrared
       • Its energy is ionising as it knocks off electrons off atoms
         • It can cause sunburn as the skin cells absorb the UV rays in the sunlight
           • This can cause serious problems to the body as it can cause skin cancer, cell mutation and even damage to the eye
     • Detected to see forged bank notes
       • Fluorescence is a property of certain chemicals where UV is absorbed and then visible light is emitted
   • X-rays
     • Radiographers in hospitals take X-ray photographs of people to see if they have broken bones
       • They pass through flesh although it can pass denser material such as bones
         • However X-rays can cause cancer so people have to wear lead aprons and stand behind a lead screen to keep exposure of X-rays minimum
   • Gamma rays
     • Has a very high frequency waves such as Gamma rays and X-rays which are also ionising and carry more energy than UV rays
       • This causes even more damage to the cells as body tissues are being destroyed, cell mutation can occur and also cancer
     • Radiotherapy is the treatment of cancer using gamma rays
       • Also it can sterilise surgical instruments to kill bacteria and microbes
   • All of these waves travel at the same speed
     • EM waves with shorter frequencies have a bigger wavelength
       • EM waves with higher frequencies have a shorter wavelength
   • Infrared
     • Is similar to microwaves however it has a higher frequency and carries more energy so if the body is exposed a lot to this radiation then you can get skin burns
     • Infrared can monitor temperature which is also known as heat radiation
       • It is given out by hot objects and the hotter the object the more infrared radiation is released
         • It can be detected by night vision equipment, heat loss through a house's uninsulated roof
           • infrared uses other equipment such as remote controls, mobile phones/ computers, security systems and grills/ toasters