# Edexcel GCSE physics UNIT 1: universal physics

THESE REVISION CARDS ARE USEFUL FOR EDEXCEL CORE SCIENCE GCSE (PHYSICS)

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## changing ideas about the solar system

Ancient greek astronomers believed that the sun, moon, planets and stars orbited the earth in perfect circles - this was known as the Geocentric model .

in the 1600 the geocentric model was replaced by the heliocentric model

The model was introduced by copernicus in 1543, but his ideas were not popular,it was condemed by the church. Evidence for this model was galileo observation of jupiters moon's .

He saw three stars in line near jupiter and after a week he noticed another star.He realised that these objects weren't stars but they were moons orbiting jupiter. This showed that not everything orbits the earth which makes the geocentric model wrong.

The current model's orbit are elliptical and not circular.

visible light tells us a lot about the universe, Scientists know about the universe by detecting waves from objects in space.

Naked eye made discoveries of the stars comets and planets; useful for mapping their posistions.

Telescopes magnify images so object can be seen in detail: useful at larger and closer distances. Telescopes on earth have a problem as some radiation is absorbed by the earth's atmosphere. Space telescopes overcome this issue but they are too expensive.

Photographs of the universe can be taken using telescopes-- this allows you to "ZOOM IN"  and look at objects in more detail. you can take objects at different times to compare them and fainter object can be seen through longer exposure time so you can collect more light.

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## WAVES and REFLECTION/REFRACTION

WAVELENGHT DISTANCE FROM ONE PEAK TO THE NEXT.Frequency is how many complete waves per second; measured in hertz.Amplitude is the height of the wave from mid line to peak

Waves transfer energy and information without transfering matter. Speed = Frequency x wavelenght (m/s)       (hz)               (m)         .wave speed = distance / time( m/s)                (m)         (s)

Transverse waves , the vibrations are at 90 degrees to the direction of travel .Longitudinal waves. the vibrations are along the same direction of travel

Reflection IS WHEN A WAVE HITS a boundary between one medium and another. (its energy is reflects) angle of reflection= angle of incidence

The light is reflected due to change in density.

Refraction = waves travel at different speeds in substances which have different densities.

Optical Fibres use infrared to transmit data

Ionising radition is emitted all the time by radioactive sources when their nuclei decay.

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Planets reflect sunlight

some scientists are looking for signs for life

SETI looks for radio signals from other planets

Robots and Probes can collect data and samples : robots collect soil and rock samples back to analyse.

Light pollution makes it hard to pick out dim objects

Air pollution can reflect and absorb light coming from space.

X-rays telescopes are a good way to "see" high tempurature events in spacelike exploding stars

Radio telescopes were responsible in the discovery of cosmic microwave background.

Spectrometer is a tool used to analyse the light given out by stars and galaxy.

Galaxies more futher away apear more red then they should be.

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Nebula = clouds of dust and gas                                                                                                         gravitional energy is coverted to kinetic energy which is converted to heat energy.

When temperature is high enough, hydrogen nuclei undergoes a thermonuclear fusion to form helium nuclei.a star is formed. it enters a long stable period which the force of gravity pulling everything inward.

This is called the main sequence star.Eventually the hydrogen in the core begins to run out and the star swells into a red giant. a small/ meduim sar like the star ejects the outer layer of gas as a planetary nebula . this leaves behind a hot, dense core ( white dwarf) which disapears

Big stars glow brightly and undergo more fusion and expands. they will explode in a supernova. The supernova ejects  gas into space leaving a dense core called a NEUTRON STAR. If the star is big enough this will become a BLACK HOLE.

Red shift is when frequencies are lower then they should be they shifted towards the red end of the spectrum. cmb is when microwave radiation is detected outside space which supports the big bang as energy started expanding.

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Power = current x voltage

primary voltage/secondary voltage = no of turns on primary / secondary.

transformers work in a.c not d.c

power= energy/times

cost= power x time x cost of 1 kwh

effciency=useful energy output/ total energy x 100

triangulation only works if you have 3 seismometer distance arcs and where they cross at one place called the epicentre of the earthquake

Space telescopes overcome this issue but they are too expensive.

Photographs of the universe can be taken using telescopes-- this allows you to "ZOOM IN"  and look at objects in more detail. you can take objects at different times to compare them and fainter object can be seen through longer exposure time so you can collect more light.

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