Lenses Flashcards
How do lenses form images
By refracting light and changing its direction
What are the main 2 types of lenses
Convex
Concave
What happens to a convex lens and what does it do to light
It bulges outward
Causes rays of light parallel to axis to be brought together at the principle focus
What do concave lenses do and what do they do to light rays
The lens caves inwards
Causes rays of light parallel to axis to spread out
What is the axis of a lens
A line passing through the middle of the lens
What is the principal focus of a
Convex lens
Concave lens
Convex - rays hitting the lens parallel to axis all meet
Concave - point where rays hitting the lens parallel to axis appear to all come from
What is the focal length
The distance form the centre of the lens to the principal focus
What are the 3 rules of refraction in a convex lens
Incident ray parrallel to axis refracts through lens and passes through principal focus on otherside
Incident ray passing though the principal focus refracts though lens and travels parallel to axis
Incident ray passing though centre of lens carries on in same direction
What are the 3 rules for refraction in concave lens
Incident ray parallel to axis refracts through lens and travels in line with principal focus
Incident ray passing through the lens towards the principal focus refracts through lens and travels parallel to axis
Incident ray passing though centre carries on in the same direction
What is a real image
Where the light from the object comes together to form an image on a screen
What is a virtual image
The rays are diverging so the light from the object seems to be coming from a completely different place
When do you get virtual images
When looking in mirror
Magnifying lens
How do you describe an object
How big it it
If it’s upright or inverted relative to object
Real or virtual
What type of image does a concave lens always produce
A virtual image
That is upright, smaller and on the same side of lens as the object
How do magnifying glasses work
They create a magnified virtual image
What can’t you do with a virtual image
You can’t project a virtual image into a screen because the light rays don’t actually come from the place where the image appears to be
What is the magnification Formula
Image height / object height
What is the range of wavelengths in visible light
400-700 nm
What are opaque objects and what colour are they
They do not transmit light
They absorb some wavelengths of light and reflect others
It’s colour depends on which wavelengths of light are most strongly reflected
What do opaque objects that aren’t a primary colour reflect
Wavelengths of light corresponding to that colour
Or
Wavelengths of the primary colours that can mix tougher to make that colour
What do transparent and translucent objects do with light
They transmit light so it can pass through
What are colour filters
They are used to filter out different wavelengths of light so that only certain colours are transmitted and the rest are absorbed
What happens if you look at a red hat through a blue colour filter
The hat would appear black because red light is relegated by the hat but it’s not transmitted because the only colour that would be transmiteed would be a
Blue coloured hat
