Lenses and Ray diagrams

all lenses have a principle focus on _____ sides

both

convex lens/converging lens

A lens that is thickest in the middle, causing parallel rays of light to converge (come together) to a focus ( called the focal point). The focal length of a converging lens is positive

concave lens (diverging lens)

A lens that is thinner in the middle and gets wider at the ends , causing parallel rays of light to diverge (spread out) from a focus on the same side of the lens that the object is. The focal length of a diverging lens is negative.

how to determine if an image is real

the image is inverted

what makes a lense strong

if it has a short focal length, if it is more curved and depending on the material

what is a real image

When the light rays from the object actually do come together to form an image, which can be captured on a screen

explain an example of a real image

light rays from a spanner pass through the lens in our eye and form a real image on our retina however it is inverted but our brain just converts it so that it's upright

What is a virtual image?

formed when the diverging light rays don't come together where the image appears to be

explain an example of a virtual image

eg. in a mirror the image appears to be behind the mirror however there can't actually be any ray behind the mirror as it's a solid object that light can't pass through so it's only a virtual image formed from virtual rays

how to draw a ray diagram of a concave lens

1. pick a point near to the top of the object and draw a horizontal line running through the lens that is parallel to the axis and one diagonal line running through the centre of the lens

2. the first ray is refracted however not the second one that runs through the centre of the lens

3. to find the position of the image draw a dotted line from the point where the refracted ray hits the lens, back to the focal point

4. the point where the rays cross is the top of our image

how to draw a ray diagram for a convex lens

1. same initial process as concave lens ( draw one horizontal line and one running through the centre of the lens)

2. the light ray will be refracted so that it passes through the focal point on the other side of the lens and carries on going

3. find the point where the light rays cross and this is the top of your image

what size will the image be if the object is more than 2x the focal length?

smaller

what size will the image be if the object is exactly 2x the focal length?

the same size as the object

what size will the image be if the object is in between F and 2F?

image will be larger than the object

what happens to the image if the object is between the focal point and the lens itsef

the refracted rays won't ever meet, so to find our image we must trace it back using virtual rays

what images do convex lenses form

real and virtual images