Heliocentric - Sun is at the centre of the solar system.
Geocentric - The earth is that the centre of the solar system. It was
accepted because peope could not feel the earth moving or in motion.
Our solar system is called the Milky Way.
Planets (from closest to the sun):
Mercury, Venus, Earth, Mars, Jupiter,
Saturn, Uranus, Neptune.
Galileo observed that Jupiter had four
moons around Jupiter. He checked another
time and noticed the moons has moved.
This meant that the moons were orbiting
Jupiter and therefore proving the
geocentric model wrong.
Waves
Transverse waves: - The pattern of disturbance is at right
angles to the direction of movement. The oscillation of
transverse wave is perpendicular to the direction of energy
transfer. E.g. Electromagnetic wave and secondary
earthquakes. These do not need a medium to travel through
Longitudinal waves: - The pattern of disturbance is in
the same direction as the direction of wave movement.
The oscillation is parallel to the direction of energy
transfer. These need a medium to travel through.
Waves are regular patterns of disturbance. They transfer
energy and information from one point to another
without any transfer of matter. Waves can be produced
in ropes, springs and on the surface of the water.
Amplitude is the maximum vertical
disturbance caused by a wave e.g. its
height.
Wavelength is the distance between
corresponding points on two successive
disturbances.
Frequency is the number of waves produced
(or passing a particular point) in one second.
Refraction
When a ray of visible or infrared
light travels from glass, perspex or
water into air, it is refracted
(changes direction)
Reflection
Some light is also reflected from the
boundary. The angle of incidence = the
angle of reflection.
Wave speed
Wave speed (m/s) = Frequency (Hz) x Wavelength (m)
Wave speed (m/s) = Distance (m) / Time taken (s)
Observing the universe/ Telescopes
Before Galileo's discoveries in 1610, all observations were
made by the unaided or naked eye. This had many
drawbacks because what can be seen with the naked eye
depends on the weather and the quality of the individuals
eye sight. In cities, light pollution can also be a problem
A simple telescope consists of two different
converging lenses. A converging lens is made of
perspex or glass with two curved surfaces, thicker in
the middle than at the edges. This shape allows the
lens to bring together (converge) light into a focus by
refracting it.
The distance from the middle of the lens to the focus
is called the focal length. If the lens is held up to the
light (e.g. a window), an inverted image (of the
window) can be seen on a piece of paper held on the
other side. An image that can be projected onto a
screen is said to be a real image.
The piece of paper or the lens can be moved until the image is sharp
(focused). The distance from the lens to the image is the focal length,
which can be measured. For a given type of glass, the thickness of the lens
will determine its focal length - so a thicker lens means a shorter focal
length.
A simple telescope can be expensive to make
large, good quality lenses which is why the
first successful reflecting telescope was built
in 1668, it had two mirrors and an eyepiece.
Objective lens: - Collects light to form an image.