Lenses Flashcards
Name the two types of lenses
Convex and concave
Describe a concave lens
Caves inwards
Causes parallel rays of light to spread out
Describe a convex lens
Bulges outwards
Causes parallel ray of light to converge at a principle focus
Where is the principle focus of a convex lens
Where rays hitting the lens parallel to the axis meet
Where is the principle focus of a concave lens
Where rays hitting the lens parallel to the axis appear to come from
Rules of refraction of convex lens
An incident ray parallel to the axis refract through the lens and passes through the principle focus on the other side
An incident ray passing through the principle focus refracts through the lens and travels parallel to the axis
An incident ray passing through the centre of the lens carries on the same direction
Rules of refraction of concave lens
An incident ray parallel to the axis refract through the lens and passes in line with the principle focus (so appears to have originated from the principle focus)
An incident ray passing through the lens towards the principle focus refracts through lens and travels parallel to the axis
An incident ray passing through the centre of the lens carries on in the same direction
What is a real image?
Where the light from an object comes together to form an image on a ‘screen’, like an image in the retina
What is a virtual image?
The rays are diverging so the light from an object appears to be coming from a completely different place
How do magnifying glasses work?
They create a magnified virtual image
the object being magnified must be closer to the lens than the focal length
