Astrophysics Flashcards
what are the 2 types of optical telescope and what lens do they use
refracting and reflecting telescopes. they both use convex lenses
what’s another name for a convex lens
a converging lens
what are the 5 key features on a ray diagram
principle axis
lens axis
principal focus
axial rays
focal length
what is an axial ray
a ray that is parallel to the principal axis
what are the 4 key steps when drawing ray diagrams with 1 lens
-draw an axial ray from the top of the object, and is refracted and goes through the focus point
- draw a ray from the top of the object straight through the centre of the lens axis
-draw a ray through the focal point on the left side and parallel from the lens axis
-draw the object
what is the scenario for an object more than 2f away
image position-between f-2f
orientation- inverted
magnified/diminished-diminished
application- camera
what is the scenario for an object at 2f
image position- at 2f
orientation- inverted
magnified/diminished- same size
application- inverter
what is the scenario for an object between f-2f
image position- beyond 2f
orientation-inverted
magnified/diminished- magnified
application-projector
what is the scenario for an object closer than f
image position- same side as object
orientation-upright
magnified/diminished-magnified
application-magnifying glass
what is the difference between real and virtual images
real images of inverted and virtual ones are not.
in the lens equation, what does it mean when v is negative
its a virtual image. if its positive-its real
how do you calculate the length of the telescope
fo+fe
how do you calculate magnification
M=fo/fe
how do refracting telescopes work
they use 2 lenses to form a magnified image. objective (larger/closer to image) and eyepiece (smaller/ further from image)
how do you calculate to get the greatest magnification
having the objective focal length a high as possible
how would you get a clear image
make sure the 2 focal lengths meet at the same point
what are the steps for drawing a ray diagram with 2 lenses
-Draw a non-axial ray through the centre of the
objective lens axis to the eyepiece lens axis
-Draw two parallel rays either side
-These should meet at the focus and then stop on the
eye lens axis
-Draw a construction line that starts from where the rays cross over and passes through the centre of the eyepiece lens
-The three rays emerge parallel to this line
how do you calculate magnification with angles
M= angle subtended by image/
angle subtended by object
how do reflecting telescopes work
they use a parabolic mirror to reflect the rays instead of lenses.
a secondary mirror is placed before the focal point which reflects the rays through the hole in the mirror, emerging parallel
this is know as the cassegrain telescope
what is a CCD
CCD-charged coupled device
used to take digital photos eg. camera
what are the physical characteristics of a CCD
consists of a series of silicon picture elements (pixels), which are very small (not pixels on a screen)
beneath each one is a potential well, which traps electrons. and above is a filter that only allows certain colour photons through
how do CCDs work
- filter only allows certain wavelengths of light to hit the pixels
- photons cause electrons to be released into the potential wells. electrons released is proportional to intensity of the photons
- the charge is then collected in the wells. and the amount of charge and the filter tells the computer what colour and brightness is displayed
what is quantum efficiency equation
number of photons detected/ X100
number of photons incident
what are the advantages of CCDs (quantum efficiency)
quantum efficiency=
CCDs- 80%
photographic film- 4%
naked eye- 1%
what are the advantages of CCDs
exposing film to too much light it gets saturated, which a CCD doesn’t
CCDs can detect a larger range of light (invisible spectrum)
the minimum resolvable distance is 10microm compared to 100microm for naked eye (CCDs see finer detail)
CCDs have longer exposure to capture fainter images
