Total Internal Reflection
LEARNING
OBJECTIVES
Core
•Describe the formation of an optical image by
a plane mirror, and give its characteristics
• Recall and use the law angle of incidence =
angle of reflection
Describe an experimental demonstration of
the refraction of light
• Use the terminology for the angle of
incidence i and angle of refraction r and
describe the passage of light through parallelsided transparent material
• Give the meaning of critical angle
• Describe internal and total internal
reflection
Describe the action of a thin converging lens
on a beam of light
• Use the terms principal focus and focal
length
• Draw ray diagrams for the formation of a
real image by a single lens
• Describe the nature of an image using the
terms enlarged/same size/diminished and
upright/inverted
Supplement
Describe the formation of an optical image by a
plane mirror, and give its characteristics
• Recall and use the law angle of incidence =
angle of reflection
Recall and use the definition of refractive
index n in terms of speed
• Recall and use the equation sin I / sin r=n
• Recall and use n = 1 / sin c
• Describe and explain the action of optical
fibres particularly in medicine and
communications technology
Draw and use ray diagrams for the formation of
a virtual image by a single lens • Use and
describe the use of a single lens as a
magnifying glass • Show understanding of the
terms real image and virtual image
Refraction of light by a
semi-circular block.
Refracted Ray
R
Angle of
Incidence
Incident Ray
I
Angle of
Refraction
Refraction of light by a
semi-circular block.
Refracted Ray
When a ray of light travels
through a semi-circular block,
the ray will be refracted ………
R
Angle of
Incidence
Incident Ray
I
Angle of
Refraction
Refraction of light by a
semi-circular block.
Refracted Ray
When a ray of light travels
through a semi-circular block,
the ray will be refracted ………
R
Angle of
Incidence
Incident Ray
I
Angle of
Refraction
Reflected Ray
…… but there will also
be some reflection.
Refraction of light by a
semi-circular block.
As the incident ray approaches
the ‘critical angle’
(approximately 42o) the
refracted ray travels at rightangles to the normal.
Refracted Ray
Incident Ray
Reflected Ray
There is now
more internal
reflection
Refraction of light by a
semi-circular block.
If the incident ray now enters the block at an
angle greater than the critical angle (42o) no
light is refracted.
Incident Ray
Reflected Ray
Refraction of light by a
semi-circular block.
If the incident ray now enters the block at an
angle greater than the critical angle (42o) no
light is refracted.
Incident Ray
Reflected Ray
All light is now reflected at the boundary. This
is known as TOTAL INTERNAL REFLECTION
Refraction of light by a
semi-circular block.
Medium
Critical
angle
Water
49o
Perspex
42o
Glass
41o
Diamond
24o
Incident Ray
If the incident ray now enters the block at an
angle greater than the critical angle (42o) no
light is refracted.
Reflected Ray
All light is now reflected at the boundary. This
is known as TOTAL INTERNAL REFLECTION
Refraction Calculations
Refraction Calculations
Supplement
Snell’s Law
When light is
refracted, an increase
in the angle of
incidence i produces
an increase in the
angle of refraction r.
Refraction Calculations
Supplement
Snell’s Law
When light is
refracted, an increase
in the angle of
incidence i produces
an increase in the
angle of refraction r.
Sin i = constant
Sin r
Refraction Calculations
Supplement
Snell’s Law
Air
i = 15o
Glass
r = 10o
sin 15o = 0.26
sin 10o = 0.17
= 1.5
Supplement
Refraction Calculations
Snell’s Law
Air
i = 15o
i = 45o
Glass
r = 10o
r = 28o
sin 15o = 0.26
sin 10o = 0.17
= 1.5
sin 45o = 0.71
sin 28o = 0.47
= 1.5
Supplement
Refraction Calculations
Snell’s Law
Air
i = 15o
i = 45o
i = 60o
Glass
r = 10o
r = 28o
r = 35o
sin 15o = 0.26
sin 10o = 0.17
= 1.5
sin 45o = 0.71
sin 28o = 0.47
= 1.5
sin 60o = 0.87
sin 35o = 0.57
= 1.5
Refraction Calculations
Snell’s Law
…and Refractive Index
Supplement
Refraction Calculations
Snell’s Law
…and Refractive Index
Refractive Index = Sin i
Sin r
Supplement
Supplement
Refraction Calculations
Snell’s Law
…and Refractive Index
Refractive Index = Sin i
Sin r
Air
i = 45o
Water
RI =
1.33
?
Supplement
Refraction Calculations
Snell’s Law
…and Refractive Index
Refractive Index = Sin i
Sin r
RI = sin i
sin r
Air
i=
Water
RI =
1.33
45o
?
1.33 = sin 45o
sin r
sin r = sin 45o
1.33
sin r = 0.532
r = 32o
Refraction Calculations
Snell’s Law
…and Refractive Index
Supplement
…and Critical Angles!
Supplement
Refraction Calculations
Snell’s Law
…and Refractive Index
…and Critical Angles!
If the angle of incidence is
greater than the critical
angle, we will get total
internal reflection.
Supplement
Refraction Calculations
Snell’s Law
Critical angle
Incident Ray
c
Refracted Ray
…and Refractive Index
…and Critical Angles!
If the ray direction is
reversed, the angle of
incidence is now 90o, and the
angle ‘c’ is now the angle of
refraction (critical angle).
Supplement
Refraction Calculations
Snell’s Law
Critical angle
Incident Ray
c
Refracted Ray
…and Refractive Index
…and Critical Angles!
If the ray direction is
reversed, the angle of
incidence is now 90o, and the
angle ‘c’ is now the angle of
refraction (critical angle).
RI = sin i = sin90o
sin c
sin c
Supplement
Refraction Calculations
Snell’s Law
Critical angle
Incident Ray
c
Refracted Ray
…and Refractive Index
…and Critical Angles!
If the ray direction is
reversed, the angle of
incidence is now 90o, and the
angle ‘c’ is now the angle of
refraction (critical angle).
RI = sin i = sin90o
sin c
sin c
RI =
1
sin c = 1
sin c
RI
Supplement
Refraction Calculations
Snell’s Law
…and Refractive Index
…and Critical Angles!
If the RI of glass = 1.5: sin c = 1 = 0.67
1.5
Critical angle
Incident Ray
c
Refracted Ray
c = 42o
If the ray direction is
reversed, the angle of
incidence is now 90o, and the
angle ‘c’ is now the angle of
refraction (critical angle).
RI = sin i = sin90o
sin c
sin c
RI =
1
sin c = 1
sin c
RI
Refraction Calculations
Snell’s Law
…and Refractive Index
Supplement
…and Critical Angles!
If theindex
RI of glass
sin c = 1 is
= 0.67
c = 42o
The refractive
of =a1.5:
medium
usually
1.5
denoted as ‘n’.
Critical angle
Ray
For a medium ofIncident
refractive
index n: sin c = 1
n
c
Supplement
Refraction Calculations
Snell’s Law
…and Refractive Index
…and Critical Angles!
If theindex
RI of glass
sin c = 1 is
= 0.67
c = 42o
The refractive
of =a1.5:
medium
usually
1.5
denoted as ‘n’.
Critical angle
Ray
For a medium ofIncident
refractive
index n: sin c = 1
n
c
eg. What is the critical angle for diamond if the refractive index (n) = 2.42?
sin c = 1
n
=
1
2.42
= 0.413
critical angle for diamond = 24.4o
LEARNING
OBJECTIVES
Core
•Describe the formation of an optical image by
a plane mirror, and give its characteristics
• Recall and use the law angle of incidence =
angle of reflection
Describe an experimental demonstration of
the refraction of light
• Use the terminology for the angle of
incidence i and angle of refraction r and
describe the passage of light through parallelsided transparent material
• Give the meaning of critical angle
• Describe internal and total internal
reflection
Describe the action of a thin converging lens
on a beam of light
• Use the terms principal focus and focal
length
• Draw ray diagrams for the formation of a
real image by a single lens
• Describe the nature of an image using the
terms enlarged/same size/diminished and
upright/inverted
Supplement
Describe the formation of an optical image by a
plane mirror, and give its characteristics
• Recall and use the law angle of incidence =
angle of reflection
Recall and use the definition of refractive
index n in terms of speed
• Recall and use the equation sin I / sin r=n
• Recall and use n = 1 / sin c
• Describe and explain the action of optical
fibres particularly in medicine and
communications technology
Draw and use ray diagrams for the formation of
a virtual image by a single lens • Use and
describe the use of a single lens as a
magnifying glass • Show understanding of the
terms real image and virtual image
Lenses
What phenomenon is evident in lenses?
https://wiki.brown.edu/confluence/display/PhysicsLabs/PHYS+0080+BC
Converging (Convex) Lens
http://www.shokabo.co.jp/sp_e/optical/labo/lens/lens.htm
Converging Lens
F
Optical
Center
C
f
Ray Diagram for Converging Lens
Principal Axis
http://facstaff.gpc.edu/~pgore/PhysicalScience/ray_diagram_sample.jpg
Rules for Ray Diagrams for Converging Lens
• A parallel ray refracts through the focal point.
• A ray through the opticalcenter of the lens
continues straight.
• A ray coming through the focal point, refracts
parallel to the principal axis.
Lenses and Refraction
Converging
lens
Lenses and Refraction
Convex lens
Concave lens
Converging
lens
Diverging lens
Lenses and Refraction
Converging
lens
Principal focus
Focal length
Lenses and Refraction
Convex lens
Concave lens
Converging
lens
Diverging lens
Principal focus
Focal length
Principal focus
Focal length
Lenses and Refraction
What happens to
light as it passes
through the lens?
Convex lens
Lenses and Refraction
What happens to
light as it passes
through the lens?
Convex lens
Lenses and Refraction
What happens to
light as it passes
through the lens?
Convex lens
Lenses and Refraction
What happens to
light as it passes
through the lens?
As light passes through the
first face of the lens it
bends towards the normal
(refraction)
Convex lens
Lenses and Refraction
What happens to
light as it passes
through the lens?
As light passes through the
first face of the lens it
bends towards the normal
(refraction)
Convex lens
As light passes through the
second face of the lens it
bends away from the normal
(refraction)
Lenses and Refraction
What happens to
light as it passes
through the lens?
As light passes through the
first face of the lens it
bends towards the normal
(refraction)
Convex lens
As light passes through the
second face of the lens it
bends away from the normal
(refraction)
Lenses and Images
Rays from a distant object brought to focus on
a screen by a convex lens.
Object
Convex
lens
Image
Lenses and Images
Rays from a distant object brought to focus on
a screen by a convex lens.
Object
Convex
lens
Image
The image on the
screen is real and
inverted (upsidedown)
Lenses and Images
Rays from a distant object brought to focus on
a screen by a convex lens.
Object
Light rays from a distant object are
considered to be parallel to each
other, so the image passes through
the principal focus.
Convex
lens
Image
The image on the
screen is real and
inverted (upsidedown)
Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
F1
F
Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
Standard Ray 1 – passes
through the centre of the lens
object
F1
F
Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
Standard Ray 1 – passes
through the centre of the lens
object
F1
Standard Ray 2 – parallel to
the principal axis, and then
passes through F after leaving
the lens.
F
Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
Standard Ray 1 – passes
through the centre of the lens
object
F1
Standard Ray 3 – passes
through F1, and then leaves
the lens parallel to the
principal axis.
Standard Ray 2 – parallel to
the principal axis, and then
passes through F after leaving
the lens.
F
Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
Standard Ray 1 – passes
through the centre of the lens
object
F1
Standard Ray 3 – passes
through F1, and then leaves
the lens parallel to the
principal axis.
Standard Ray 2 – parallel to
the principal axis, and then
passes through F after leaving
the lens.
F
The image
produced is
real, inverted
and smaller
than the
object.
Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
Standard Ray 1 – passes
through the centre of the lens
object
F1
Standard Ray 3 – passes
through F1, and then leaves
the lens parallel to the
principal axis.
Only two of the
standard rays are
required to work
out where they go.
Standard Ray 2 – parallel to
the principal axis, and then
passes through F after leaving
the lens.
F
The image
produced is
real, inverted
and smaller
than the
object.
Lenses and Ray Diagrams
- Predicting where a convex lens will form an image.
Standard Ray 1 – passes
through the centre of the lens
object
F1
Standard Ray 2 – parallel to
the principal axis, and then
passes through F after leaving
the lens.
F
Standard Ray 3 – passes
through F1, and then leaves
the lens parallel to the
principal axis.
Only two of the
standard rays are
required to work
out where they go.
As the object is
moved closer towards
the lens, the image
becomes bigger and
further away.
The image
produced is
real, inverted
and smaller
than the
object.
Uses of Convex Lenses
1. In a projector
Object at distance further than twice the focal length (2f) from the lens:
•the image is:
Real
Diminished (smaller)
Inverted
Between F and 2F
If the object is placed at exactly twice the focal length (2f) from the
lens:
Diagram showing the formation of a real image with the object at
2f
•In this case the image is:
Real
Same size as the object
Inverted
•Lenses can be used to form images of objects placed in front of them
•The location (and nature) of the image can be found by drawing a ray diagram:
Uses of Convex Lenses
1. As a magnifying glass
F1
F
Object
between F1
and lens
Uses of Convex Lenses
2. As a magnifying glass
F1
F
Object
between F1
and lens
Uses of Convex Lenses
The rays appear to be coming from a
position behind the lens. The image
is upright and magnified, and it is
called a virtual image because no
rays actually meet to form it and
the image cannot be formed on a
screen.
2. As a magnifying glass
F1
The image
is virtual,
upright
and
magnified.
F
Object
between F1
and lens
LEARNING
OBJECTIVES
Core
•Describe the formation of an optical image by
a plane mirror, and give its characteristics
• Recall and use the law angle of incidence =
angle of reflection
Describe an experimental demonstration of
the refraction of light
• Use the terminology for the angle of
incidence i and angle of refraction r and
describe the passage of light through parallelsided transparent material
• Give the meaning of critical angle
• Describe internal and total internal
reflection
Describe the action of a thin converging lens
on a beam of light
• Use the terms principal focus and focal
length
• Draw ray diagrams for the formation of a
real image by a single lens
• Describe the nature of an image using the
terms enlarged/same size/diminished and
upright/inverted
Supplement
Describe the formation of an optical image by a
plane mirror, and give its characteristics
• Recall and use the law angle of incidence =
angle of reflection
Recall and use the definition of refractive
index n in terms of speed
• Recall and use the equation sin I / sin r=n
• Recall and use n = 1 / sin c
• Describe and explain the action of optical
fibres particularly in medicine and
communications technology
Draw and use ray diagrams for the formation of
a virtual image by a single lens • Use and
describe the use of a single lens as a
magnifying glass • Show understanding of the
terms real image and virtual image
PHYSICS – Total Internal Reflection and
Lenses