Lenses
Refraction is the bending/spreading out of waves as they change medium. This means that they
travel from one medium to another medium with a different refractive index.
There are two types of lenses, a converging convex lens, which is used in glasses or a diverging
concave lens. The rays bend to the fatter part of each type of lens. Converging lenses have a
positive power and focal length. With a converging lens the focal point is in front of the lens
and both real and virtual images. Diverging lenses have a negative power and focal length.
With a diverging lens the focal point is behind the lens and only virtual images are formed.
Lens axis
Focal length Different focal planes
Principle axis
Focal point
B
·
A
↳
⑲ A
⑱
A
D
The image is enlarged, The image is virtual, The image is
inverted, real and the focal upright and diminished, upright
length is 2.5 f enlarged. and virtual
Real images are formed when light from the object passes through another point. Real images are
displayable on screens. The rays are actually present at the image and the image is on the other
side of the lens.
Virtual images are formed when light from the object appears to come from another point and they
are not displayable on screens. The rays are not present at the image and the image is on the same
side as the image.
Refraction is the bending/spreading out of waves as they change medium. This means that they
travel from one medium to another medium with a different refractive index.
There are two types of lenses, a converging convex lens, which is used in glasses or a diverging
concave lens. The rays bend to the fatter part of each type of lens. Converging lenses have a
positive power and focal length. With a converging lens the focal point is in front of the lens
and both real and virtual images. Diverging lenses have a negative power and focal length.
With a diverging lens the focal point is behind the lens and only virtual images are formed.
Lens axis
Focal length Different focal planes
Principle axis
Focal point
B
·
A
↳
⑲ A
⑱
A
D
The image is enlarged, The image is virtual, The image is
inverted, real and the focal upright and diminished, upright
length is 2.5 f enlarged. and virtual
Real images are formed when light from the object passes through another point. Real images are
displayable on screens. The rays are actually present at the image and the image is on the other
side of the lens.
Virtual images are formed when light from the object appears to come from another point and they
are not displayable on screens. The rays are not present at the image and the image is on the same
side as the image.
