Thin Converging Lenses
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Transcript of Thin Converging Lenses
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LENSLE
N
S
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Learning Objectives
Describe the action of a thin converging lens
on a beam of light.
Define the term focal length.
Draw ray diagrams to illustrate the
formation of real and virtual images of an
object.
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What is a Lens?
Is any piece of transparent glass or
plastic
Is specially moulded such that it either
converges light rays passing through it
to a point or makes them moredivergent
Via this process forms images.
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Converging VS Diverging Lens
Converging LensConverging Lens
Thicker in the middle than at the ends
Eg:
Diverging lensDiverging lens
Thinner in the middle than at the endsEg:
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Converging VS Diverging Lens
Converging LensConverging Lens
Brings light rays travelling through it to
one point. i.e. converges the light rays
passing through it.
Diverging lensDiverging lens
Spreads out the light rays travellingthrough it. i.e. diverges the light rays
passing through it.
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Main Features of a Thin Converging LensMain Features of a Thin Converging Lens
Optical centre -
For a symmetrical lens, this is the point
midway between the lens surfaces on its
principal axis.
Optical Centre
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Main Features of a Thin Converging LensMain Features of a Thin Converging Lens
Principal axis -
This is the imaginary line passing
symmetrically through the opticalcentre of the lens.
c
Principal axis
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Main Features of a Thin Converging Lens
Focal length (f)-
This is the distance between the optical
centre C and the principal focus F
F
Optical centre
Focal length (f)
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Refraction due to ThinRefraction due to Thin
Converging lensConverging lens
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Refraction Rules for a Converging Lens
RULE 1RULE 1
A light ray travelling parallel to the principal axis
refracts through the lens and travels through the
focal point on the opposite side of the lens.
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Refraction Rules for a Converging Lens
RULE 2RULE 2
A light ray traveling through the focal point on
the way to the lens will refract through the lens
and travel parallel to the principal axis.
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Refraction Rules for a Converging Lens
RULE 3RULE 3
Any ray that is either non-parallel to the
principal axis or that which does not
pass through the focal point will
converge at the same point as the rays
mentioned in rules 1 and 2 provided
they all emanate from the same point.
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Object and Image Distance
Image DistanceObject Distance
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Exercise
Click on the link below and follow the
instructions on the next slide.
LENS
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Instructions for using Lens Applet
Firstly,
click and change the light rays to Principal rays
on the tab. Click and drag the Object to any position
Observe how the image changes as your objects is
moved:5. Towards the lens;
6. Away from the lens.
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Instructions for using Lens Applet
Secondly,
click and change the refractive index of the lens
by dragging on the tab. Observe how the image changes as your refractive
index of the lens
4. Is increased;2. Is decreased.
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Instructions for using Lens AppletFinally,
click and change the curvature radius of the lens
by dragging on the tab.
Observe how the image changes as your radius ofthe lens
4. Is increased;
5. Is decreased.
You may play with it and use what you have learnt
to answer the questions in Worksheet Set A.
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To Conclude
Read the Thin Converging Lenses Notes
Attempt Worksheet Set A , print it out and
submit on next lesson.
