P1a Topic 1

P1a Topic 1

1. Changing ideas about the solar system

   • Geocentric model- the sun, moon, planets and stars orbitted earth in perfect circles
   • Heliocentric model- earth and planets orbit the sun.
     • Introduced by Copernicus
   • Galileo- observed jupiters moons using a telescope, discovered it had 4 orbiting it.
     • Proved geocentric model wrong- not everything orbits Earth

2. Visible light

   • Early astronomers made observations just using naked eye
     • However most astronomical bjects are so far away that naked eye is only useful for mapping their positions
   • Telescopes magnify so distant objects can be seen in more detail
     • Can also see objects at larger distances
       • Many discoveries have been made because of them and they have helped us understand more about the universe
     • Photographs can be taken using telescopes
       • Allows us to zoom in and look in more detail
       • Makes it easier to monitor objects by photographing at different times
       • Can also see faint objects by allowing long exposure time to collect more light

3. Waves

   • Wavelength- distance from one peak to the next
   • Frequency- how many complete waves pass per second (Hz)
   • Amplitude- height of wave
   • Speed- how fast it goes
   • Transverse wave- vibrations at 90 degrees to direction of travel
     • eg. Light and other EM waves and S-waves
   • Longitudinal- vibrations along same direction (parallel) to direction of travel
     • eg. Sound and ultrasound and P-waves

4. Reflection and refraction

   • Reflection
     • When a wave hits a boundary between one medium and another- some energy reflected
     • Angle of reflection(r)= angle of incidence (I)
     • Happens because of change in density. Whenever a wave reaches a medium with a different density, some of the wave is reflected at the boundary
   • Refraction
     • Waves travel at different speeds in substances with different densities
     • EM waves travel slowly in denser media and sound waves travel faster
     • If light waves slow down, they bend towards the normal and if they speed up, they bend away
     • If a wave hits a boundary head on it changes speed but not direction
     • If a wave meets a medium at an angle, it changes direction because parts of the wave slow down before others

5. Real and virtual images

   • A real image is where light from an object comes together to form an image on a screen
   • A virtual image is when the rays are diverging, so the light appears to be coming from elsewhere
     • When looking in the mirror you see a virtual image because your face appears to be behind the mirror
     • Magnifying lenses create virtual images which look bigger and further away than they actually are

6. Lenses

   • Converging lenses- focus light
     • Convex- bulges outwards
     • Causes parallel rays of light to converge to a focus
   • Axis- the line passing through the middle of the lens
   • Focal point- where rays meet (each lens has one in front and one behind)

7. Telescopes

   • Refracting telescope- two converging lenses
     • Rays from object come from so far away that they are parallel when they reach objective lens
     • Objective lens converges rays to form a real image at focal point of objective lens
     • Rays of light from the real image enter the eyepiece lens. The lens spreads them out so they leave at a wider angle and fill more of the retina- magnifies image
   • Reflecting telescope- mirrors and converging lens
     • Concave mirror collects parallel rays of light from an object
     • Larger mirror reflects this light onto a smaller convex mirror placed in front of the larger mirrors focal point
     • The smaller mirror reflects light through a hole in the large collecting mirror, real image formed behind mirror
     • Converging eyepiece lens used to magnify the image