SNC2D-OPTICS
Some objects make their own light. We call them luminous sources. (sun,light bulbs)
Most things you see do NOT make their own light but reflect it from a luminous source. They are non-luminous objects. (moon)
Light travels in straight lines
Light does not require a medium
A medium is any physical substance through which energy can be transferred
Examples: water, air, oil
Light can travel in empty space, therefore it does not require a medium to travel through
What is light?
Light is visible energy transferred through electromagnetic radiation
Light is part of the ELECTROMAGNETIC SPECTRUM.
Most of it is invisible radiation. We only see a small portion of it – the visible spectrum
Invisible Radiation
Makes up the entire electromagnetic spectrum except for the visible light spectrum
1) Radio Waves
AM/FM radio
TV signals
Cellphone communication
Radar
Astronomy (e.g. discovery of pulsars)
Body scanning at Airports
2) MicrowavesTelecommunications (eg cell phone towers)
Microwave ovens
Astronomy (e.g, background radiation associated with the Big Bang)
3) Infrared Light
Remote controls
Sensors that turn on faucets or stop garage doors from closing
Heat detection
Keeping food warm
Astronomy (e.g. discovering the chemical composition of celestial bodies)
Physical therapy
4) Ultraviolet Light
Black lights in theatre special effects
Tanning and sunburn to skin
Increases risk of skin cancer
Stimulates production of vitamin D
Kills bacteria in food and water
Astronomy (e.g. discovering the chemical composition of celestial bodies)
5) X-rays
Medical imaging (e.g. teeth and broken bones)
Security equipment (e.g. scanning of luggage at airports)
Cancer treatment
Astronomy (e.g. study of black holes)
6) Gamma RaysCancer treatment
Astronomy (e.g. study of nuclear processes in the universe)
Product of some nuclear decay
Visible Light
Visible light is any electromagnetic wave that the human eye can detect.
Visible light is composed of a continuous sequence of colours called the visible spectrum
The Colours Associated with Visible Light
We can identify seven distinct colours:
Red, Orange, Yellow, Green, Blue, Indigo, Violet
We use the acronym ROYGBIV to help us remember
Sources of Light
Incandescence
Light emitted when a material is being
heated.
An incandescence light bulb has a tiny
tungsten wire that gets very hot and glows
brightly when electric current passes
through it.
Electric Discharge
Light caused by passing an
electric current through
a gas
Neon glows red
Helium glows gold
Argon a pale violet-blue
Examples: Street/store
signs and lightning bolts
Fluorescence
Light produced when an object absorbs
Ultraviolet light and immediately releases the
energy as visible light.
Fluorescent dyes commonly added to
detergents.
Phosphorescence
Emission of light from a
material during and AFTER
exposure to an energy source.
A light that is emitted while
the source is exposed to
ultraviolet light, and continues
to emit light after the
electromagnetic radiation has
been removed.
Phosphorescence
Materials glow long
after they have
absorbed ultraviolet
light.
Examples: glow in
the dark toys
Chemiluminescence
Light produced from a
chemical reaction without
an increase in temperature.
Examples: glow sticks
Bioluminescence
A form of
chemiluminescence
that occurs in living
organisms.
Chemical reactions
in living cells
produce light.
Bioluminescence
Little or no heat is
produced.
Example: firefly,
jellyfish, krill,
deep-sea star, black
dragonfish
Triboluminescence
production of light
from friction as a
result of scratching,
crushing, or rubbing
certain crystals.
The Light-Emitting Diode (LED)
electronic device that allows an electric
current to flow in only one direction.
uses semiconductors - a material, such as
silicon, that allows an electric current to flow
in only one direction.
no filament.
does not produce a lot of heat.
energy efficient.
LASER = Light
Amplified by
Stimulated Emission
of Radiation
A laser consists of
electromagnetic
waves of exactly the
same energy level,
traveling in unison in
exactly the same
direction.
Laser light is:
Very pure in colour
Intense
Concentrated in one
narrow beam
Can travel great
distances without
spreading out.
Images in a Plane Mirror
Using Light Rays to Locate an Image
Light rays and
the laws of
reflection help
determine how
and where an
image is formed
in a plane mirror.
Using Light Rays to Locate an Image
We know that light
travels in a straight line.
This belief is so strong
that that when our eyes
detect reflected light
from a plane mirror our
brain projects the light
rays backwards into a
straight line.
Using Light Rays to Locate an Image
The brain thinks the light rays originate from
behind the mirror. This produces a virtual
image.
Using Light Rays to Locate an Image
Virtual image: an image in which light does
not actually arrive at or come from the image
location.
The light only appears to come from the image
Using Equal Perpendicular Lines to
Locate an Image
Two characteristics of images:
The distance from the object to the mirror is
the same as the distance from the image to
the mirror.
The object-image line is perpendicular to the
mirror surface.
Characteristics of Images
We can use the acronym SALT for Size,
Attitude, Location, and Type, to
remember these four image
characteristics.
Types of Curved Mirrors
Concave (converging) mirror
Edges curve towards you
Ex. Makeup mirror
Convex (diverging) mirror
Edges curve away from you
Ex. Side-view mirrors in cars
Curved Mirrors & Laws of
Reflection
The Laws of Reflection apply to curved
mirrors
Recall:
The angle of reflection is always equal to the
angle of incidence
The incident ray, the normal, and reflected
ray all lie in the same plane
A concave mirror is
also known as a
converging mirror.
This is due to rays of
light coming together
or converging.
Characteristics of Concave Mirrors
In order to study curved mirrors, we need to know a few
terms:
The point C is the
centre of curvature
since it is the
centre of the
imaginary sphere
or cylinder that the
mirror is a part of.
Characteristics of Concave Mirrors
In order to study curved mirrors, we need to
know a few terms:
The line that passes
through the centre
of curvature and
the centre of the
mirror is called the
principal axis
Characteristics of Concave Mirrors
In order to study curved mirrors, we need to
know a few terms:
Point V is called the
vertex since it is the
point where the
principal axis meets
the mirror.
Reflection in Concave Mirrors
Each incident ray has its own normal,
which is perpendicular to the mirror at that
point
4 Golden Rules
A light ray parallel to the principal axis is
reflected through the focus (F).
A light ray through the focus (F) is reflected
parallel to the principal axis
A light ray through the centre of curvature (C) is
reflected back through the centre of curvature
A ray aimed at the vertex (V) will reflect back at
the same angle below the principal axis
Characteristics of Images when
an object is Beyond C, At C, or
Between C and F
Reflected rays actually meet in FRONT of
the mirror
Form an UPSIDE DOWN image
Form a REAL image
Real image: any
image that can be
formed on a screen is
a real image because
light rays are actually
arriving at the image
location
Common Uses of Concave Mirrors
Light Concentration for Heating:
Concave mirrors are used to focus light for heating
purposes. For this the food or substance that has
to be heated is placed at the focus of a large
concave reflector. After reflection, sunlight
converges on the substance and heats it.