Physics

Physics

1. visible light and the solar system

   • heliocentric model and geocentric
     • geocentric meant everything orbited the earth. the earth is the center of the solar system
       • ancient greeks
     • heliocentric meant the sun was in the center and the planets orbit the sun
       • copernicus used galileos observations of jupiters moons. these shown that not everything orbited Earth. 
   • scientists detect waves from objects in space to discover things.
     • used to use naked eye but developed telescopes to help see further but have problems.
       • space telescopes overcome these problems but are expensive
     • telescopes magnify things so distant objects can be seen easier.
       • they can also take photographs
   • waves
     • wavelength, amplitude, frequency and speed
       • wavelength is distance from one peak to the next amplitude is the height of the wave frequency is how many complete waves there are per second. (hz) speed is how fast the wave is travelling at.
     • speed=frequency X wavelength
       • wave speed = distance / time
     • transverse waves and longitudinal waves
       • transverse the vibrations are at 90degrees to the direction of travel. light waves, s-waves longitudinal waves- vibrations are along the same direction. sound, ultrasound, p-waves
     • waves can be reflected and refracted
       • when a wave hits a boundary between one medium and another, some of its energy is reflected
       • waves travel at different speeds through different densities. when a wave corsses a boundary into a different boundary it changes speed making the wave refract
   • converging lenses are used to focus light
     • this lens causes parallel rays of light to converge together to form a focus
       • the focal point is where rays hitting the lens parallel to the axis meet. 
     • focal length is the distance from the lens to its focal point.
   • refracting telescopes use 2 converging telescopes. reflecting telescopes use mirrors and a converging lens
     • refracting telescope - forms a real image at focal point of the objective lens  reflecting telescope - concave mirror collects light from space and reflects light onto smaller lens. a real image is formed behind the mirror which then get magnified using a converging eyepiece. 

2. electromagnetic spectrum

   • there are 7 types of electromagnetic (EM) waves
     • radio waves, micro waves, infra red, visible light, ultra violet, x-rays, gamma rays
       • radio waves have the longest wavelengths and gamma rays have the shortest wavelength. radio waves have the lowest frequency and gamma rays have the highest.
       • infrared was discovered by herschel in 1800. he recorded the temperature of the colours in white light and noticed that the temperature increases from violet to red. he took the temperature just past the red end where there was no visible light and discovered this was the hottest. this was infrared.
       • ritter discovered ultraviolet radiation soon after in 1801. he knew silver chloride turned black when exposed to light. he recorded the times in different light and noticed it was quicket at the blue end. he put it just past the violet end and saw the quickest change. this was ultraviolet radiation., and invisible form of light
     • all EM waves are transverse
     • all EM waves travel at the same speed in a vacuum.
   • some EM radiation can be harmful to people
     • micro waves can heat human cells. mobile phones use micro waves
     • infrared can carries more energy than micro waves because it has a higher frequency it can cause burning on the skin and heat cells.
     • ultraviolet is ionising. it can cause cell mutations or destruction and skin cancer.
     • gamma/x-rays are very high frequency waves and are also ionising. they can penetrate further into the body and can cause cell mutation or destruction leading to tissue damage or cancer.
   • different waves have different uses
     • radio waves are used in communications like tv and radio and to transmit satellite signals micro waves are used for staellite communication and mobile phones. microwave ovens use a different wavelength. infrared radiation can be used to monitor temperature because its given out by all hot objects. optical fibres use IR to transmit data. the naked eye can see visible light when light enters your eye. ultraviolet is used to detect forged bank notes.  x-rays are used to see inside objects. x-rays easily pass thgrough flesh so its the amount of radiation thats absorbed (or not) that gives you an x-ray image.  gamma rays are used in radiotherapy to treat cancer. it has to be carefully aimed to kill cancer cells and not too many normal cells. sterilisation of food and surgical instruments uses gamma rays because it kills microbes. 
   • there are three types of ionising radiation, gamma, beta and alpha.
     • ionising radiation is emitted by radioactive sources when their nuclei decay. when it happens it produces on of the three types.

Bilder und Dateien der Mindmap