Lenses and the Eye Flashcards
What is the magnification formula?
magnification = image height / object height
What is the equation for power?
- Power (Diopter or m^-1) = 1 / focal length (m)
- P = 1 / f
What are the three rules for refraction in a diverging lens?
- an incident ray parallel to the axis refracts through the lens and travels in line with the principal focus
- an incident ray passing towards the principal focus refracts through the lens and travels parallel to the axis
- an incident ray passing through the centre of the lens carries on in the same direction
What type of image is formed in diverging lenses?
- it always produced a virtual image
- it is always the right way up, smaller than the object and on the same side of the lens as the object
Which lens always has a positive power?
- converging lens
What 3 things do you need to describe an image properly?
- how big it is compared to the object
- whether it is upright or inverted relative to object
- real or virtual
What do you have to record when drawing diagrams?
- position of object
- rea or virtual
- image orientation
- image size
- image position
Which lens always has a negative power?
- diverging lens
What are the three rules for refraction in converging lenses?
- an incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side
- an incident ray passing through the principal focus before entering the lens will refract through the lens and travel parallel to the axis
- an incident ray passing through the centre of the lens carries on in the same direction
What are diverging lenses
- a concave lens, caving inwards
- causes parallel rays of light to diverge (spread out)
What are converging lenses?
- a convex lens, bulges outwards
- it causes parallel rays to converge (come together)at the principal focus
How does the refractive index affect power and focal length?
- the greater the refractive index, the more powerful the lens
