2.3 Lenses Flashcards
What is the optical centre of a lens?
The centre of the lens, denoted O or C.
What is the principal axis?
A line passing through the optical centre at right angles to the centre of the lens.
What is the focal point/principal focus?
Where rays parallel to the principal axis converge in a convex lens or appear to diverge in a concave lens after passing through the lens. Denoted symbol F.
What is the focal length?
Distance O to F, ie from the centre of the lens to the principal focus.
What is a real image?
An image formed by the actual intersection of rays.
What is a virtual image?
An image formed by the apparent intersection of rays.
What is magnification?
The ration of the image height to the object height.
What is accomodation?
The cornea partly refracts the light rays which then go through the lens which finely adjusts the focusing. The lens does this by changing its thickness.
What is myopia?
- This is also known as short sight.
- When a person can see things close clearly, but things far away are blurred.
What 2 things can cause myopia?
- The lens is too powerful.
- The eye is too long.
What is hypermetropia?
- Also known as long sight.
- When a person can see things far away clearly, but thing nearby are blurred.
What 2 things can cause hypermetropia?
- The lens is too weak.
- The eye is too short.
How can hypermetropia be corrected?
By the use of a converging lens which will refract the rays towards the lens to be further refracted to meet at the retina.
How can myopia be corrected?
By the use of a diverging lens which will diffract the rays away from the lens in which the lens will then refract the rays to meet at the retina.
