Physics paper 3 keywords

Dependent Variable

The variable that is measured or observed in an experiment; it changes in response to the independent variable.

Independent Variable

The variable that is purposely changed or manipulated in an experiment to test its effect on the dependent variable.

Linearity

The extent to which a graph or relationship between variables forms a straight line, showing a consistent rate of change.

Sensitivity

The ability of an instrument or experiment to detect small changes or differences in the measured variable.

Uncertainty

A measure of how much a measured or calculated value might differ from the true value; shows the possible error in a measurement.

Zero Error

A type of systematic error that happens when an instrument shows a reading even though the true value is zero.

focal length

distance between the centre of lens and the principle focus

astronomical refracting telescope

uses objective and eyepiece lens (converging lens) where objective has large focal length and eyepiece has short focal length and the final image is virtual, inverted and magnified

Cassegrain telescopes

uses mirrors instead of lenses where concave primary mirror collects light and convex secondary mirror reflects light back and passes through a hole in primary mirror, telescope is short than its effective focal length

chromatic aberration

different wavelengths of light are refracted by different amounts in a lens, causing them to focus at different points produces a blurred image with coloured edges.

spherical aberration

rays of light passing through different parts of a spherical lens or mirror focus at different points, causing the image to appear blurred

solution for chromatic aberration

use achromatic doublet or mirrors to reflect wavelengths equally

solution for spherical aberration

use aperture stop/parabolic mirror blocks out outer rays or reflects parallel rays to same focus

increasing size of objective lens/mirror

increases diameter of objective because it is proportional

Rayleigh criterion

two point sources are just resolvable when the central maximum of one diffraction pattern coincides with the first minimum of the other theat similar to wavelength/diameter

structure, positioning and use of single dish radio telescope

large parabolic dish focuses radiation onto receiver can be ground-based but must in isolated location and can observe galaxies, stars and black holes

structure positioning and use of infrared telescope

large concave mirror focusing light onto detector must be cooled with cryogenic fluid to avoid interference and must be in space as infrared can be blocked by atmosphere and can observe cooler regions in space

structure positioning and use of ultraviolet telescope

Cassegrain config that focuses radiation onto solid state devices and must be in space as ultraviolet can be blocked by ozone layer and can observed interstellar medium and star formation regions

structure, positioning and use of x-ray telescope

combination of hyperbolic and parabolic mirrors to focus radiation onto CCD and must be in space as x-rays are blocked by the atmosphere and can observer high-energy events and areas

structure, positioning and use of gamma telescope

no mirrors radiation passes through detectors made of layers of pixels and must be in space as gamma is blocked by atmosphere and can observe gamma ray bursts, quasars, black holes and sonar flares

apparent magnitude

how bright star appears from earth

absolute magnitude

how bright star appears 10 parsecs from earth

Hipparcos scale

logarithmic scale of apparent magnitude based on the brightness of stars as observed from Earth

parsec

distance at which a star would have a parallax angle of 1 arcsecond when observed from Earth (1/3600th of a degree)

light year

distance travelled by light in a vacuum in one year

black body

perfect absorber and perfect emitter of radiation

supernova

explosion of a star increases absolute magnitude

type1a supernova

result of white dwarf core accumulating too much matter from binary partner and exploding above critical mass

type 2 supernova

single star collapses under its own gravity causing outer layers to be ejected

black hole

region of space where gravity is so strong that nothing, not even light, can escape from it.

dark energy

hypothetical form of energy that causes the expansion of the universe to accelerate

formula for radius of black hole

R=2GM/c²

doppler effect

wavelength increases frequency decreases

red shift

wavelength of light from an object increases because the object is moving away from the observer

Hubbler’s law

velocity of receding galaxies is proportional to their distance from earth

quasars

extremely luminous and distant objects powered by supermassive black holes at the centre of a young galaxy

exoplanets

planets that are not in our solar system

detecting exoplanets

radial velocity method and transit method

CCD detector

charge coupled devices used in telescopes to detect and record images of astronomical objects

Balmer lines

visible spectral lines produced when electrons in hydrogen atoms fall from higher energy levels to the n=2energy level

transit method

detects exoplanets by measuring the small drop in brightness of a star when a planet passes in front of it

what is collecting power proportional to?

collecting power proportional to diameter^2

big bang theory evidence

abundance of H and He and CMBR

angle formula with arc length

s/d

age of planet or universe

1/Hubbles constant

what does schwarzchilds radius represent

radius of event horizon of a black hole

black body assumptions

perfect black bodies and no light absorbed/scattered by interstellar material between star and observer

life cycle of star

nebula,protostar,mainsequence,giant,white dwarf or supernova

how does CCD work

semiconductor device converts a photon into a current

formula for distance to a nearby star

d=1/parallax angle

converging lens

lens that causes parallel rays of light to come together at a point called the principal focus

adv of refracting telescope

simple design,good image quality,lens protection

adv of reflecting telescope

no chromatic abberation,cheaper to scale up

angular resolution

smallest angular separation between two objects that can still be seen as two distinct objects

why can wide telescopes resolve but narrow telescopes cant

better angular resolution

formula for velocity between stars in a binary system

2pixr/T

what were quasars discovered as

bright radio sources showing large optical redshifts