P1a Topic 1 Revision

Geocentric Model

• Accepted model of the universe from the time of the ancient Greeks until the 1950s
• Greek astronomers believed that the Sun, Moon, planets and stars all orbited the Earth in perfect circles
• The moon was considered a planet and had its own axis
• All the planets were aligned
• Could not keep up with the more precise observations, many corrections had to be made. 

Heliocentric Model - Copernicus

• Replaced geocentric model in 1600s; first introduced in a book by Copernicus in 1543.
• The book showed astronomical observations could be explained without having the Earth as the centre of the Universe.
• States that the Earth and planets all orbit the Sun, which is at the centre of the Universe.
• The planets weren’t aligned
• Stars not on an axis and were scattered around the solar system
• Model violated philosophical and religious beliefs

Heliocentric Model – Kepler

• States that the orbits of the planets weren’t circular but elliptical
• Used religious arguments 
• One of the first scientists to use a telescope

Heliocentric Model – Galileo

•  New stars (milky way made up of stars)
•  Rings of Saturn
•  Planets are disks, not pinpoints of light like the stars
•  Showed problems with the geocentric model
•  Phases of Venus backed up model
• 1610 – Galileo observed Jupiter when he saw three stars in a line near the planet. The next evening, he saw these moved in the wrong direction in the night sky. After a week, a fourth star appeared. These stars never moved away from Jupiter and seemed to be carried along with the planet – these were moons orbiting Jupiter. Not everything was in orbit around the Earth; geocentric model proved wrong. 

• As technology has improved, our idea of the Solar System and the Universe had changed e.g. the telescope led to the discovery of Uranus.
• Scientists find out about things in the Universe by detecting waves from objects in space. Some objects like stars give out lots of visible light.
• We can see the planets in our Solar System because they reflect sunlight.                                    

Observations

• Many very important discoveries of stars, comets and planets were made by using the naked eye. These observations are only really useful for mapping their positions.
• Telescope magnify images, so distant objects can be seen in more detail as well as seeing objects that are at larger distances. They help us learn more about what the Universe is made up of.
• Photographs using telescopes allow you to ‘zoom in’ and look at objects in more detail. It makes it easier to monitor an object by taking pictures at different times to compare and share them. You can also see faint objects by allowing a long exposure time so you collect more light. 

• WAVELENGTH: Distance from one peak to the next
• FREQUENCY: Complete waves/second (Hz)
  
• AMPLITUDE: Height of wave (from mid-line to peak)
• Waves transfer energy and information without transfering matter

SPEED (M/S) = FREQUENCY (Hz) X WAVELENGTH (m)

WAVE SPEED (M/S) = DISTANCE (m) / TIME (s)

• TRANSVERSE WAVES: Vibrations are at 90degrees to the direction of travel of the wave
  • Light and other EM waves
  • S-Waves
  • Waves on strings and springs
  • Ripples on water
• LONGITUDINAL WAVES: Vibrations along the same direction as the wave is travelling
  • Sound and ultrasound
  • P-waves
  • Slinky spring when you push and pull the end

Reflection

• The law states: angle of incidence = angle of reflection
• Some energy is reflected at the boundary when there is a change in density from two mediums

Refraction

• When a wave crosses at a boundary between two substances, it changes speed
• EM waves travel slower in denser media (usually); Sound waves travel faster
• When light passes from air to glass, it slows down and bends towards the normal but when passing from glass to air again, it speeds up and bends away from the normal

Images

• Real Image: Light from an obeject come together to form an image on a screen
• Virtual Image: Rays are diverging so the light from an object appears to be coming from a completely different place e.g. looking at an object through a magnifying glass where the virtual image looks bigger and further away than the object actually is

CONVERGING LENS

• Convex lens (bulging out) causes parallel rays of light to converge together to a focal point
  
• The focal point is where rays hitting the lens parallel to the axis all meet
• Converging lenses produce real images where the image is upside down

FOCAL LENGTH

• All converging lenses have a focal length. This tells you how much they magnify things. The shorter the focal length the more they magnify things
  • Set up equipment near a window with the lens directed at a distant object
  • Make sure the object is well lit/luminous and clamp the lens at one end of a track
  • Clamp a piece of white card further down the track
  • Move the card along the track until image is focused
  • Clamp the piece of card at place where best image is seen
  • Use a ruler to measure the distance between the centre of the lens to the card
• Object is beyond FL F and closer than 2F = object refracted and image bigger and inverted
• Object is beyond 2F, further from lens = object refracted and image smaller and inverted
• Object is closer than F =  Virtual, reflected image (2 lines never meet and image can't focus)

Refracting Telescope

• Rays from distant object are parallel when reaching the objective lens which converges and foucses the light to form a real image at the focal point
• The eyepiece lens has a shorter focal length, spreading out the rays of light and magnifying them so they leave at a wider angle
• The more distant the object, the clearer the real image is
  • Large telescopes are expensive and heavy

Reflecting Telescope

• Contain two concave mirrors and an eyepiece lens
  
• The larger mirror reflects rays of light directed onto the second mirror which is infront of the first mirror's focal point
• The image that appears to be behind the second mirror is virtual
• The second, smaller mirror focuses the light onto a focal point where a real image is created
• The eyepiece lens magnifies the image to make it visible to the human eye
  • Cheaper, more portable, further into the universe, bigger (collects more light)