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Lenses
- Converging lenses
- Parallel rays of light that as through a
converging lens are refracted so that they
converge to a point.
- This point is called the prinicipal focus. The distance from
the centre of the lens to the principal focus is the focal length.
- This point is called the prinicipal focus. The distance from
the centre of the lens to the principal focus is the focal length.
- Because the light can pass through the lens
in either direction, there is a principal focus
on either side of the lens.
- If the object is further away from the lens than the
principal focus, and inverted, real image is
formed. The size of the image depends on the
position of the object. The nearer the object is to
the lens, the larger the image.
- If the object is nearer to the lens than the
principal focus, an upright, virtual image is
formed behind the object. The image is
magnified - the lens acts as a magnifying glass.
- The magnification can be calculated using:
- Magnification = Image Height / Object height
- Magnification = Image Height / Object height
- Parallel rays of light that as through a
converging lens are refracted so that they
converge to a point.
- Diverging lenses
- Parallel rays of light that pass through a diverging (concave)
lens are refracted so that they diverge away from a point. This
point is called the principal focus.
- The distance from the centre of the lens to the principal
focus is the focus length.
- Because the light can pass through the lens in either
direction, there is a principal focus on either side of the
lens.
- The image produced by a diverging
(concave) lens is always virtual.
- Parallel rays of light that pass through a diverging (concave)
lens are refracted so that they diverge away from a point. This
point is called the principal focus.
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