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GCSE level Physics exam revision notes on
light and reflection
Reflected light: Part 5.
Uses
of curved and plane mirrors
and other reflecting surfaces, total
internal reflection in fibre optic cables
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[ KEY
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See also Part 7.
How a reflecting
telescope works
INDEX of physics notes: Light reflection
and the
uses of plane and curved mirrors
5.
The uses of curved and plane mirrors and other reflecting surfaces, total
internal reflection
(remember
angle of reflection i always
equals the angle of reflection r with respect to the 90o
normal)
Reminder: The reflection rule (angle i =
angle r) applies whatever the shape of the mirror.
However, the shape of the mirror surface
is important for what you want to do with the mirror!
Mirrors can be all shapes and sizes depending
on their uses, including distorting your shape at a fun-fair!
The most familiar use is a plane mirror in
the home - you see a 'perfect' image of yourself, but it is laterally
inverted - your left become right and right becomes left! Its called lateral
inversion. However, 'top' and 'bottom' are still the same!
Note on the use of mirrors and safety equipment
Good reflectors used on bicycles and
safety clothing because they are designed so that the light is directed back
in one direction from where it came from e.g. the headlamps of a car.
The reflectors cover a wide range of
angles so you cannot see a clear reflected image.
They are often made of red plastic
and act as a colour filter, so you see the red warning colour.
A periscope is a simple method of
observing something from a different height than that of your eye.
It is used to observe things when there is a
barrier or other obstacle in the way.
You can buy a simple one using
plane
mirrors (left diagram above) for watching golf with spectators in front of
you!
The periscopes of submarines require
something a little more sophisticated.
The right-hand diagram shows how you use
45o triangular prisms instead of mirrors.
Prisms have a higher
optical quality and note that the inside surfaces of solid '3D' prisms can act
as a mirror.
This phenomena is called 'total internal reflection'.
You can use these 45o prisms to reverse the
direction of a light beam - can you figure out how and sketch the ray diagram?
Comparing concave and convex mirrors
A concave mirror can focus light rays
to a common point F in front of the mirror (F is called the principal focus).
The distance from F to the centre of the mirror is called the focal length.
You
come across the same terms when you study
lenses.
This type of lens is used in reflecting telescopes (example further down).
A concave mirror is described as a converging mirror, for example it can
converge the Sun's rays to a focus point to provide a workable solar heating
system.
A shaving mirror is a concave mirror because it can produce an upright
magnified image.
See also Part 7.
How a reflecting
telescope works
A convex mirror disperses the rays and
the focal point F is behind the mirror.
Convex mirrors give you a wide field
of view and collect light over a wide angle.
Convex mirrors are used by the driver
on a bus, shop security and side-mirrors on cars to give a wide view of the road
behind and to the side of a vehicle.
Use of
a concave parabolic mirror in head lamps of floodlights
A parabolic concave mirror
is used to produce a powerful beam of light.
In car headlamps the light from
the bulb (filament or LED) is collected by the mirror and reflected to produce
an approximately parallel beam of rays to illuminate a narrow field of view
ahead of the vehicle - the mirror acts with a small angle of
divergence.
So, in reality the diagram isn't quite
correct because you want the rays to diverge a little to produce a wider beam to
illuminate more of the road ahead.
You can make small changes to the parabolic
shape to change the dispersion of the beam.
A parabolic array of mirrors can be used to make a
solar furnace,
reaching temperatures of over 2000oC.
French scientists have been experimenting with
solar furnaces since 1949.
Hot countries like Spain are doing increasing
research, no doubted prompted lately by climate change, since
solar energy is free and doesn't produce carbon dioxide!
See
https://en.wikipedia.org/wiki/Solar_furnace
Uses of
total internal reflection
The internal surface of optical fibres
acts as a mirror - another case of total internal reflection, this time in fine
glass strands which allow the transmission of visible light rays and information
signals over long distances with minimum loss of intensity (amplitude).
INDEX notes: Light reflection and
uses of plane & curved mirrors
Key points
on
reflection and mirrors: Uses of plane mirrors and convex/concave curved mirrors
Information
sources for Doc Brown's key points: IGCSE-GCSE physics are based on
textbooks & syllabus-specifications for students taking the UK AQA, Edexcel,
OCR 21st Century Science, OCR Gateway science suite, WJEC, CCEA and CIE GCSE
physics 9-1 level science examinations
A structured set of summary revision notes on the uses of plane and curved mirrors (concave
and convex), tailored to the GCSE/IGCSE Physics
specifications across WJEC, CCEA, CIE, AQA, Edexcel,
and OCR.
Uses of Plane Mirrors
Key Properties
- Flat reflective surface
- Forms a virtual,
upright, laterally inverted image
- Image is same size
and same distance behind the mirror
Common Uses
- Household mirrors:
Bathrooms, dressing tables
- Periscopes:
Used in submarines and tanks
- Optical instruments:
Redirecting light paths
- Decorative and architectural
design: Enhancing space
perception
Uses of Curved Mirrors
1.
Concave Mirrors (Converging)
Properties
- Curved
inwards
- Can form real or virtual
images depending on object position
- Focuses parallel rays to a
focal point
Applications
| Use |
Purpose |
| Reflecting telescopes |
Focus distant starlight |
| Shaving/makeup mirrors |
Magnify face for detail |
| Dental mirrors |
Provide magnified view of teeth |
| Headlamp reflectors |
Focus light into a beam |
| Solar cookers |
Concentrate sunlight for heating |
2.
Convex Mirrors (Diverging)
Properties
- Curved
outwards
- Always forms virtual,
diminished, upright images
- Provides a
wide field of view
Applications
| Use |
Purpose |
| Vehicle wing mirrors |
Wider view of traffic |
| Security mirrors |
Surveillance in shops and
buildings |
| Road safety mirrors |
Visibility around blind corners |
| Anti-theft mirrors |
Monitor hidden areas |
Common Misconceptions about the nature and
use of concave mirrors and concave mirrors
- Concave mirrors always magnify
→ Correction: They magnify only when the object is close
to the mirror.
- Convex mirrors produce real
images
→ Correction: They always produce virtual images.
- Plane mirrors flip images
upside down
→ Correction: They laterally invert, not vertically
flip.
- All curved mirrors magnify
→ Correction: Convex mirrors reduce image size.
Exam Tips about the nature and use of
concave mirrors and concave mirrors
- Be able to identify mirror
types from diagrams.
- Know the image characteristics
for each mirror type.
- Practice ray diagrams
for concave and convex mirrors.
- Link mirror uses to wave
behaviour and reflection laws.
- Use correct terminology:
virtual, real, inverted,
upright, magnified, diminished.
Typical Exam Board Specific syllabus
content about the nature and use of concave mirrors and concave mirrors
|
Focus Areas |
| Mirror types, ray diagrams,
practical applications. |
| Image properties, uses of mirrors,
reflection law. |
| Detailed ray tracing and mirror
comparisons. |
| Emphasis on real-world uses and
image characteristics. |
| In-depth ray diagrams, mirror
equations, and applications. |
Keywords, phrases and learning objectives for
the reflection of visible light rays -
Uses
of curved mirrors and plane mirrors
Be able to describe and explain the uses of curved
parabolic concave mirrors, curved convex parabolic mirrors
and plane mirrors and other reflecting surfaces e.g. car headlamps,
shaving mirror.
Know, describe and explain total internal
reflection and its use in fibre optic cables.
WHAT NEXT?
TOP of page
INDEX of physics notes
on light reflection and mirrors
INDEX of all notes on waves, radiation,
astronomy etc.
Revision notes on examples of uses of
plane mirrors & curved mirrors described & explained based on the syllabus-specifications
for students taking IGCSE/GCSE level physics examinations, summary
revision notes and key points on examples of uses of plane mirrors &
curved mirrors described & explained for students taking the AQA
igcse/gcse physics notes on examples of uses of plane mirrors & curved mirrors
described & explained, Edexcel gcse
physics notes on examples of uses of plane mirrors & curved mirrors
described & explained, OCR 21st century GCSE
physics notes on examples of uses of plane mirrors & curved mirrors
described & explained, OCR gateway
GCSE physics notes on examples of uses of plane mirrors & curved
mirrors described & explained, WJEC gcse physics notes on examples
of uses of plane mirrors & curved mirrors described & explained, CCEA
gcse physics notes on examples of uses of plane mirrors & curved mirrors
described & explained for students taking CIE Cambridge igcse
physics, exam revision notes on
examples of uses of plane mirrors & curved mirrors described &
explained, useful for US grade 9-10 physics courses,
importance of total internal reflection
at a smooth surface explained and use in fibre optic cables
in GCSE level physics, What you need to know about total internal
reflection at a smooth surface explained and use in fibre optic
cables for
GCSE level
physics,
Explaining the use of total internal reflection at a smooth surface
explained and use in fibre optic cables knowledge in GCSE level physics, Examples of
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INDEX notes: Light reflection and
uses of plane & curved mirrors
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