AS Module
5b |
|
In this option, fundamental physical principles are applied to the study and interpretation of the Universe. Students will gain deeper insight into the behaviour of objects at great distances from Earth and discover the ways in which information from these objects can be gathered. The underlying physical principles of the optical and other devices used are covered and some indication given of the new information gained by the use of radio astronomy. Details of particular sources and their mechanisms are not required. | |
15.1 Lenses and optical telescopes |
|
15.1.1 Lenses |
Principal focus, focal length of converging lens power = 1/f Formation of images by a converging lens Ray diagrams 1/u + 1/v = 1/f |
15.1.2 Astronomical telescope consisting of two converging lenses |
Ray diagram to show the image formation in normal
adjustment Angular magnification in normal adjustment M =
angle subtended by image at eye Focal lengths of the lenses M = fo |
15.1.3 Reflecting telescopes |
Focal point of concave mirror Cassegrain arrangement, ray diagram to show path of rays through the telescope as far as the eyepiece. Relative merits of reflectors and refractors including a qualitative treatment of spherical and chromatic aberration. |
15.1.4 Resolving power |
Appreciation of diffraction pattern produced by circular
aperture, Airy disc Resolving power of telescope, Rayleigh criterion, q »
λ |
15.1.5 Charge coupled device |
Structure and operation of the charge coupled device Quantum efficiency of pixel > 70% |
15.2 Radio astronomy |
|
15.2.1 Single dish radio telescopes, general principles and resolving power |
Similarities with optical telescopes: objective,
mirror, detector, power µ diameter 2 , tracking of source Differences from optical telescopes: resolving
power, limit of resolution Objective diameter, precision of about
λ /20 needed in shape of dish. |
15.3 Classification of stars |
|
15.3.1 Classification by luminosity | Relation between brightness and apparent magnitude |
15.3.2 Apparent magnitude, m |
Relation between intensity and apparent magnitude Measurement of m from photographic plates and distinction between photographic and visual magnitude not required |
15.3.3 Absolute magnitude, M |
Parsec and light year Definition of M, relation to m m –
M = 5 log d |
15.3.4 Classification by temperature, black body radiation |
Stefan’s law and
Wien’s displacement law General shape of black body curves, experimental verification is not required Use of Wien’s displacement law to estimate black-body temperature of sources λ max T = constant = 0.0029 mK Inverse square law, assumptions in its
application P = σ AT4 Assumption that a star is a black body |
15.3.5
Principles of the use of stellar
spectral classes
|
Description of the main classes, O B A F G K M Temperature required: need for excitation Helium absorption (O): need for higher temperature Hydrogen Balmer absorption lines (B, A): need for atoms in n=2 state Metals absorption (F, G): occurs at lower temperature Molecular bands (K, M): occur at lowest temperature |
15.3.6
The Hertzsprung- Russell diagram
power point link to stellar evidence multi-choice on the lifecycle of stars |
General shape: main sequence, dwarfs and giants Stellar evolution: path of a star similar to our Sun on the Hertzsprung- Russell diagram from formation to white dwarf |
15.3.7
Supernovae, neutron stars and black holes
PowerPoint - right mouse click and choose "save as"
|
General properties Calculation of the radius of the event horizon for a black hole Schwarzchild radius (Rs) Rs »
2GM |
15.4 Cosmology |
|
15.4.1
Doppler effect
PowerPoint - right mouse click and choose "save as" |
Df
= v and Dλ
= -v f c λ c for v « c applied to optical and radio frequencies Calculations on binary stars viewed in the plane of orbit |
15.4.2 Hubble’s law |
Red shift
v = Hd Simple interpretation as expansion of
universe; estimation of age of universe,
assuming H is
constant |
15.4.3 Quasars |
Quasars as the most distant measurable objects Discovery as bright radio sources Controversy concerning distance and power – use of inverse square law Quasars show large optical red shifts; estimation of distance |
Revision Resources |
|
Glossary - unfinished - based on last year's syllabus |
|
PH04 past module exam questions March2000, Feb96 & March97 |