P3 - Lenses And Images Flashcards
What is a converging lens?
It is convex - it bulges outwards.
What is a diverging lens?
It’s concave - it caves inwards.
What does a converging lens do?
It causes light rays to move together at the principal focus.
What does a diverging lens do?
It causes rays of light to spread out.
What is the axis of a lens?
A line passing through the middle.
What is the principal focus of a converging lens?
Where the rays and the axis meet.
What is the principal focus of a diverging lens?
The point where the rays appear to come from in front of the lens.
What is the focal length?
The distance from the centre of the length to the principal focus.
What are the 3 rules for refraction in a converging lens?
1) a ray parallel to the axis passes through the principal focus.
2) a ray passing through the principal focus travels parallel to the axis.
3) a ray passing through the centre of the lens carries on in the same direction.
What are the 3 rules for refraction in a diverging lens?
1) a ray parallel to the axis travels in line with the principal focus.
2) a ray travelling towards the principal focus travels parallel to the axis.
3) a ray passing through the lens centre 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 the eye’s retina.
What is a virtual image?
When the rays are diverging so the object appears to come from a different place.
When do you get virtual images? [2].
1) mirrors - the object/your face appears to be behind the mirror.
2) magnifying lens - the object looks bigger.
What 3 things must you include when describing an image?
1) how big it is compared to the object.
2) upright or inverted.
3) real or virtual.
How do lenses form images?
By refracting light and changing its direction.
