revision topic 11 Flashcards
how does a lens work
lens work by changing the direction of light passing through it. each section of the lens acts like a tiny prism refracting the light that goes through the lense and out
what is the convex lens
it is a lense that makes parrel lines focus on one place, it might be used as magnifying
what is the principal focus in the convex lens
the point where the parallel rays are focused
what is the concave lens
it makes parallel rays diverge
what is the principal focus in the concave lens
the point where the rays appear to come from
what is the focal length
it is the distance from the centre of the lens to the principal focus
how is a real image formed by a converging(convex) lens
it is formed when an object is beyond the principal focus because when it is formed when light rays are focused onto a screen
how is a virtual image formed by a converging (convex) lens
it is formed when the virtual image is before the principal focus because it is formed where rays appear to come from
what is the formula of magnification
image height/object height
the nature f the image formed by the lens depends on
- the focal length
2. the distance from the object to the lens
what is the principal axis
it is the line that is perpendicular to the centre of the lens
how does a camera work
cameras are transitionally convex lens where a real image it is produced on a digital screen by the pixel and there are two rules for cameras
- in distanced objects the distance between the lens and film as to be equal to the focal length
- the nearer the object to the lens is the greater the distance from the lens to the film
how is a virtual image formed in a concave lens
the image formed in the concave lens is always virtual upright and smaller than the object
what is the job of the eye lens in the eye
it focuses light on the retina
what is the job of the iris in the eye
a coloured ring of muscle it controls the amount of light entering the eye
what is the job of the pupil in the eye
the central hole formed by the iris light enters from the pupil
what is the job of the ciliary muscles in the eye
it is attached to the lens by suspensory ligaments it controls the thickness of the eye lens
what is the job of the cornea in the eye
it is a transparent layer in the eye that protects it and helps focus light on the retina
what is the job of the retina in the eye
the light-sensitive cells around the inside of the eye
what is the human range of vision
25cm to infinity
what happens if you are in a dim light
the ciliary muscles in the iris would make the pupil dilate allowing more light to be focused onto the retina from the eye lens
compare the eye and the camera
the eye as a variable focus convex lens, and the camera has a fixed focus convex lens, the eye alters the thickness of the lens by the ciliary muscles, in-camera you can just adjust the lens position, they both form a real, inverted magnification less than 1 image, the iris control the width of the pupil, in-camera you can adjust the aperture stop, and the eye has the retina while the camera has CCD for image detection
what is short sight and how does it happen and why does it happen
it is a defect that occurs when the eye cant focus on distant objects, it happens because the image is formed before the retina this is because the eye lens too powerful or the eyeball is too long
how can a short sight be treated
by using a concave lens
what is long sight and how does it happen and why does it happen
it is an eye defect that occurs when the eye cant focus on distant objects, it happens because the image is formed after the retina and this is because the eyeball is too short or the eye lens is weak
how can a long sight be treated?
by using a convex lens
the larger the refractive index
the more powerful the lens is, the shorter id focal length is, and the thinner and fatter the lens can be made because it needs to be less curved
how can short sight be treated
by using an excimer laser to make part of the cornea slightly thinner having the same effect as using a concave lens
