Telescopes Flashcards
What does a converging/convex lens do?
Brings parallel rays to focus in the focal plane
Why do the rays at the top of the converging lens diagram refract more?
It has a larger angle of incidence
What happens to the ray that hits perpendicular to the surface?
Doesn’t refract at all as it has angle of incidence of 0.
What would a more curved or thicker lens do?
It would refract light more as it is more powerful
What does a diverging/concave lens do?
It causes light to spread out as if it was coming from a virtual focus behind the lens.
What are the characteristics of a real image?
-can be projected on a screen
-rays ACTUALLY cross
-object and image are on opposite sides of the lens.
What are the characteristics of the virtual image?
-cannot be projected on the screen
-rays APPEAR to cross
-object and image are on the same side of lens
How does a simple refracting telescope work?
-It consists of two convex lenses of different focal lengths
-The objective lens of longer focal length receives parallel rays of light from distant objects
-An inverted real image of a star is formed
-the rays then refract into the eyepiece lens and the parallel rays received from our eyes will produce a virtual/inverted image
What is normal adjustment?
When the image is formed at infinity and the light rays leave the telescope parallel
how do you calculate the distance between the two lenses?
Focal length of objective+focal length of eyepiece
How to calculate angular magnification?
angle with telescope/angle without telescope.
how to calculate angular mag in normal adjustment?
focal length of objective/focal length of eyepiece.
How does a cassegrain reflector work?
-Parallel rays arrive from distant object
-primary concave mirror collects the light and then reflects it to the secondary convex
-secondary convex focuses light into small gap in into the centre of the primary
-refracted by eyepiece into parallel rays to enter the eye.
What are the benefits of a reflector?
-much easier to make a bigger primary mirror than objective lens
-collects more light therefore can see fainter objects
-bigger aperture
-chromatic abberation
-only the surface needs to be perfect and to do that you just need to polish it
What are the benefits of refractors?
-Refractor will have a wider field of view because ang mag is less
-doesn’t have the secondary mirror blocking the middle of the image
