Further Physics, Observing the Universe.
THESE CARDS ARE IN ORDER TO AID
REVISION FOR THE P7 SCIENCE EXAM.
Movement of Objects in Space.
Stars, Planets and The Moon appear to move EAST-WEST across the sky.
Sidereal Day = Time it takes the EARTH to rotate 360 degrees. ( 23H 56M)
Solar Day = 24 hours.
Stars appear to move across the sky once every 23 HOURS 56 MINUTES.
The Moon appears to move across the sky once every 24 HOURS 49 MINUTES.
Earth rotates round the sun = different stars seen at different times of year.
Planets change positions compared to background stars.
Lunar Cycle = Moon's apperance during 28 day orbit of Earth.
Solar Eclipse = Moon passes between Earth and Sun.
Lunar Eclipse = Earth passes between Sun and Moon.
Measurements of Stars.
Parallax = Thought of as movement of an object compared to it's background. This is caused by the motion of an observer.
Parallax angle of a star = Half the angle moved against the background of distant stars over a time period ( six months is often used)
Parsecs = DIstance to a star with a parallax angle of one second of an arc.
Star's intrinsic brightness = size and temperature
Star's observed brightness = intrinsic brightness and distance from earth.
Cepheid variable star = pulses, varying brightness, used to work out distance.
Stars are made of three parts:
Core = where fusion takes place
Convective Zone = Where energy is transported to surface
Photosphere = Where energy is radiated into space.. ( think photon)
A star's spectrum shows the main elements that specific star is made out of.
Life Cycle of a Star
START OF LIFE --> gravity brings gas clouds together --> Pressure, temperature and gravity increase --> Protostar forms--> Hydrogen nuclei fuse into helium nuclei --> stable star forms.
END OF LIFE ( small stars) --> core hydrogen begins to run out --> become red giants --> white dwars
END OF LIFE ( large stars) --> core hydrogen begins to run out --> become red supergiantsm --> neutron star/ black hole.
Curtis - Shapely Debate.
Fuzzy objects in the sky called Nebulae:
- Curtis believed nebulae were distant galaxies
- Shapely believed nebulae were gas clouds in OUR galaxy.
Studying Cepheid Variables provided evidence that Nebulae = distant galaxies.
SPEED OF RECESSION = HUBBLE CONSTANT X DISTANCE
(Km/s) (Mpc) (Mpc/ Km)
Pressure, Temperature and Volume.
Particles collide --> force exerted --> felt as pressure.
Volume of fluid reduced --> volume increases
Fluid heated up -->volume increases--> pressure increases ( if the volume is fixed)
Absolute temperature --> measure of temperature starting at ABSOLUTE zero ( -273 degrees) --> measured in Kelvins (K)
Kelvin converted into Degrees = subtract 273.
Degrees converted into Kelvin = add 273.
Alpha Particle Scattering Experiment
Gold foil bombarded with alpha particles --> most particles pass straight through..some were deflected or bounced back.
Conclusions = Atoms have small, dense, positive cores called nucleus. Electrons are arranged around nucleus.
Power (dioptre) = 1 / focal length
Magnification = focal length of objective lense/ focal length of eyepiece lense
Telescopes can be ground based or in space.
Angular magnification --> larger angle from distant, magnified object, object seems bigger/ closer
Radio --> long wavelength--> easily diffacted --> fuzzy image
Light --> short wavelength--> not diffracted easily --> sharp image