Convex Lens
A convex lens is thicker at the centre than at the edges.
Convex lenses are thicker at the middle. Rays of light that
pass through the lens are brought closer together (they converge). A convex
lens is a converging lens.
When parallel rays of light pass through a convex lens the
refracted rays converge at one point called the principal focus.
The distance between the principal focus and the centre of
the lens is called the focal length.
Use of Convex Lenses – The Camera
A camera consists of three main parts.
The body which is
light tight and contains all the mechanical parts.
The lens which is
a convex (converging) lens).
The film or a
charged couple device in the case of a digital camera.
The rays of light from the person are converged by the
convex lens forming an image on the film or charged couple device in the case
of a digital camera.
The angle at which the light enters the lens depends on the
distance of the object from the lens. If the object is close to the lens the
light rays enter at a sharper angled. This results in the rays converging away
from the lens. As the lens can only bend the light to a certain agree the image
needs to be focussed in order to form on the film. This is achieved by moving
the lens away from the film.
Similarly, if the object is away from the lens the rays
enter at a wider angle. This results in the rays being refracted at a sharper
angle and the image forming closer to the lens. In this case the lens needs to
be positioned closer to the film to get a focused image.
Thus the real image of a closer object forms further away
from the lens than the real image of a distant object and the action of
focusing is the moving of the lens to get the real image to fall on the film.
The image formed is said to be real because the rays of
lighted from the object pass through the film and inverted (upside down).
The Magnifying Glass
A magnifying glass is a convex lens which produces a
magnified (larger) image of an object.
A magnifying glass produces an upright, magnified virtual
image. The virtual image produced is on the same side of the lens as the
object. For a magnified image to be observed the distance between the object
and the lens must be shorter than the focal length of the lens.
A magnifying glass is a convex lens which produces a
magnified image of an object.
For a magnified image to be observed the distance between
the object and the lens has to be shorter than the focal length of the lens.
The image formed is upright, magnified and virtual.
Magnification
The magnification of a lens can be calculated using the
following formula;
As this is a ratio between heights it has no units. A
magnification of 2 means the image is twice the size of the object and a magnification
of 1 indicates an image size being the same as the object size.
Concave Lens
A concave lens is thinner at the centre than at the edges.
Concave lenses are thinner at the middle. Rays of light that
pass through the lens are spread out (they diverge). A concave lens is a
diverging lens.
When parallel rays of light pass through a concave lens the
refracted rays diverge so that they appear to come from one point called the
principal focus.
The distance between the principal focus and the centre of
the lens is called the focal length.
The image formed is virtual and diminished (smaller)
Source:http://www.passmyexams.co.uk/GCSE/physics/concave-lenses-convex-lenses.html
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Source:http://www.passmyexams.co.uk/GCSE/physics/concave-lenses-convex-lenses.html
MAU PULSA GRATIS ? Click here
