SUMMARISED FORM 4 PHYSICS NOTES
, SUMMARIZEDPHYSICSFORM4NOTES
Chapter One
THINLENSES EffectsofLensesonParallelRaysof
Light
Introduction Whenaparallelbeamoflightis
Alensisgenerallyatransparent directed towards a convex lens,
material with at least one the rays are converged at a
curved surface.
point and then diverge as they
Lenses are usually made of
glass,clearplasticorperspex. continue, [figure 1.2 (a)].
They are usually found in Whenaparallelbeamoflightis
cameras,spectaclesandeven directed towards a concavelens,
the human eye. the rays diverge as if
Alensworksbyrefractingthe theyarefromapointinfrontof the
light traversing it. lens, [figure 1.2 (b)]
TypesofLenses
Therearetwotypesoflenses,
namely:
(a) Convex(converging)lens,
(b) Concave(diverging)lens
Convex lenses are thickest at
the middle while concavelenses
are thinnest at the middle,
[figure1.1(a)and(b)].
Figure 1.2
DefinitionofTerms
1. CentreofCurvature,C
Thisreferstothecentreofthe
sphereofwhichthesurfaceof
the lens is part.
Sincealenshastwosurfaces,it
Figure 1.1 has two centres of curvature,
[figure 1.3 (a), (b) and (c)].
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, SUMMARIZEDPHYSICSFORM4NOTES
5. PrincipalFocus,F
(a) For a converging lens, it is the
point on the principal axis to which
raysparallelandclosetotheprincipal
axisconvergeafterrefraction,[figure
1.4(a)and(b)].
Figure 1.3
2. RadiusofCurvature,r
This refers to the radius of the
sphere of which the surface of
Figure 1.4
thelensispart,[figure1.3(a),
(b)and(c)].
(b) Foradiverginglens,itisthepoint on
the principal axis from which rays
3. PrincipalAxis
parallelandclosetotheprincipalaxis
Thisreferstotheimaginaryline passing
appear to diverge after refraction by
through the centres of curvatures,
the lens, [figure 1.5 (a) and (b)].
(figure1.4and1.5).
4. OpticalCentre,O
This refers to the point on the
principal axis midway between the
surfacesofthelens,(figure1.4and 1.5).
Note:
Anyrayoflightpassingthroughthis
point passes on undeviated.
Figure 1.5
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, SUMMARIZEDPHYSICSFORM4NOTES
Note:
(i) Alenshastwoprincipalfoci,one on
either side.
(ii) The principal focus of a
converginglensisrealwhilethatof a
diverging lens is virtual.
(iii) Raysthatareparallelandcloseto the
principal axis or make very small
angles with the principal axis are
known as paraxial rays.
(iv) Raysthatareparallelandfar
away from the principal axis are
known as marginal rays.
6. FocalLength,f Figure 1.6
This is the distance between the
opticalcentreandtheprincipalfocus,
[(figure 1. 4 (a) and 1.5(a)]. RAYDIAGRAMS
There are three important rays that
Note: areusedindiagramsforthelocation of
Thefocallengthofaconverginglens is images formed by lenses:
real while that of a diverging lens is (i) Arayoflightparalleltothe
virtual. principal axis
Foraconvexlens,thisray
7. FocalPlane
This is a plane perpendicular to the passesthroughtheprincipal
principalaxisandpassingthroughthe focusafterrefractionbythe
principal focus, [figure 1.6 (a) and lens, [figure 1.7(a)].
(b)]. For a concave lens, this ray
appears to emerge from the
principalfocusafterrefraction
by the lens, [figure 1.7 (b)].
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, SUMMARIZEDPHYSICSFORM4NOTES
Chapter One
THINLENSES EffectsofLensesonParallelRaysof
Light
Introduction Whenaparallelbeamoflightis
Alensisgenerallyatransparent directed towards a convex lens,
material with at least one the rays are converged at a
curved surface.
point and then diverge as they
Lenses are usually made of
glass,clearplasticorperspex. continue, [figure 1.2 (a)].
They are usually found in Whenaparallelbeamoflightis
cameras,spectaclesandeven directed towards a concavelens,
the human eye. the rays diverge as if
Alensworksbyrefractingthe theyarefromapointinfrontof the
light traversing it. lens, [figure 1.2 (b)]
TypesofLenses
Therearetwotypesoflenses,
namely:
(a) Convex(converging)lens,
(b) Concave(diverging)lens
Convex lenses are thickest at
the middle while concavelenses
are thinnest at the middle,
[figure1.1(a)and(b)].
Figure 1.2
DefinitionofTerms
1. CentreofCurvature,C
Thisreferstothecentreofthe
sphereofwhichthesurfaceof
the lens is part.
Sincealenshastwosurfaces,it
Figure 1.1 has two centres of curvature,
[figure 1.3 (a), (b) and (c)].
Page1of196
, SUMMARIZEDPHYSICSFORM4NOTES
5. PrincipalFocus,F
(a) For a converging lens, it is the
point on the principal axis to which
raysparallelandclosetotheprincipal
axisconvergeafterrefraction,[figure
1.4(a)and(b)].
Figure 1.3
2. RadiusofCurvature,r
This refers to the radius of the
sphere of which the surface of
Figure 1.4
thelensispart,[figure1.3(a),
(b)and(c)].
(b) Foradiverginglens,itisthepoint on
the principal axis from which rays
3. PrincipalAxis
parallelandclosetotheprincipalaxis
Thisreferstotheimaginaryline passing
appear to diverge after refraction by
through the centres of curvatures,
the lens, [figure 1.5 (a) and (b)].
(figure1.4and1.5).
4. OpticalCentre,O
This refers to the point on the
principal axis midway between the
surfacesofthelens,(figure1.4and 1.5).
Note:
Anyrayoflightpassingthroughthis
point passes on undeviated.
Figure 1.5
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, SUMMARIZEDPHYSICSFORM4NOTES
Note:
(i) Alenshastwoprincipalfoci,one on
either side.
(ii) The principal focus of a
converginglensisrealwhilethatof a
diverging lens is virtual.
(iii) Raysthatareparallelandcloseto the
principal axis or make very small
angles with the principal axis are
known as paraxial rays.
(iv) Raysthatareparallelandfar
away from the principal axis are
known as marginal rays.
6. FocalLength,f Figure 1.6
This is the distance between the
opticalcentreandtheprincipalfocus,
[(figure 1. 4 (a) and 1.5(a)]. RAYDIAGRAMS
There are three important rays that
Note: areusedindiagramsforthelocation of
Thefocallengthofaconverginglens is images formed by lenses:
real while that of a diverging lens is (i) Arayoflightparalleltothe
virtual. principal axis
Foraconvexlens,thisray
7. FocalPlane
This is a plane perpendicular to the passesthroughtheprincipal
principalaxisandpassingthroughthe focusafterrefractionbythe
principal focus, [figure 1.6 (a) and lens, [figure 1.7(a)].
(b)]. For a concave lens, this ray
appears to emerge from the
principalfocusafterrefraction
by the lens, [figure 1.7 (b)].
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