Transcript 08-SNC2P_(4.1+4.2)

Physics – Light and Geometric Optics
Incandescence: Light given off when an object is very
hot.
Luminescence: Light given off when an object is not
heated. There are several types of luminescence:
 Chemiluminescence – some chemical reactions emit light,
but no heat.
 Electric Discharge – gases in a tube absorb electrical energy
and emit light.
 Fluorescence - gases in a tube absorb electrical energy and
emit ultraviolet light.
 Wavelength - the distance from one place in a wave to
the next similar place on the wave; for example, the
distance from crest to crest.
The Electromagnetic Spectrum
The Electromagnetic Spectrum
 Light is a form of energy.
 Visible light is only a tiny fraction of the energy that
surrounds us every day.
 We are also surrounded by invisible light-like waves,
which together with visible light are called
electromagnetic radiation.
 Electromagnetic radiation is a wave pattern made of
electric and magnetic fields that can travel through
empty space.
 The different types of electromagnetic waves make up
what is called the electromagnetic spectrum
Radio Waves - Uses
 AM/FM radio signals
 Television signals
 Radar
 Satellite communications
 Magnetic resonance imaging machines (MRI).
Microwave - Uses
 Microwave ovens
 Satellites
 Cell phone signals
Infrared Light - Uses
 Security systems (burglar alarms, motion sensors)
 Lasers
 Night vision goggles
 Provides heat to keep food warm in restaurants.
Ultraviolet Light - Uses
 Causes skin to tan
 Increases risk of skin cancer
 Stimulates the production of Vitamin D
 Kills bacteria in food / water
 Used in detective work to reveal the presence of
substances that cannot be seen under visible light.
X-Rays- Uses
 Able to go through most things except bone and lead.
 Security equipment (i.e. At airports)
 Medical imaging (X-ray machine)
Gamma Rays - Uses
 Used to sterilize medical
equipment.
 Cancer treatment (radiation
therapy)
 Product of nuclear decay.
 White light separates into the colours of the rainbow,
including red, orange, yellow, green, blue, and violet
(ROY G BV).
 The range of different colours of light is called the visible
spectrum.
 The difference between colours of light is that each
colour has a different wavelength and frequency.
Colour
Red
Orange
Yellow
Green
Blue
Violet
Frequency (Hz)
4.3 x 1014
5.0 x 1014
5.2 x 1014
5.7 x 1014
6.4 x 1014
7.5 x 1014
Wavelength (nm)
700  Longer
600
580
550
450
400  Shorter
ACTIVITY: What Is White
Light Made Of?
Reflection, Absorption, Transmission
 Transmission: Light passes through an
object and continues travelling. Example:
Clear glass.
 Absorption: Light is absorbed by (remains
in) the object and turned into heat.
 Reflection: Light bounces off the object and
travels in another direction.
Reflection — Light Changes Direction
 In A the person sees the object because light travels to
their eyes.
 B shows that light must travel from a source (the lamp)
and then reflect off the object toward the eye.
Absorption – Light Is Converted to Heat
 The “E” in the image above appears black because the ink
absorbs all of the light that hits it.
 No light reaches your eyes from the printed “E”.
Transparent, Translucent, and Opaque Objects
 Transparent materials absorb and reflect very little light.
Example: a clear window.
 Translucent materials allow light to pass through but
scatters it in different directions.
 Opaque objects absorb and reflect light, but they do not
transmit it.
Objects can absorb some colours and reflect or
transmit others.
 Opaque objects either absorb or reflect light.
 The colour an object is determined by:
 the colours (or wavelengths) of light that are
reflected by its surface
 and the colours that are absorbed by the object.
Under white light, the tomato appears to be red
because only the red wavelength is reflected.
Under blue light, the tomato appears to be blue.
Objects can absorb some colours and reflect or
transmit others.
 The colour of an object is determined by:
 which colours (or wavelengths) of light are reflected by its
surface,
 and which colours are absorbed by the object.
The apple reflects only red light.
The pepper reflects only green light.
ACTIVITY: Exploring the properties
of light (Pin hole camera)
Rays of light travel in a straight line.
As a result, the rays investigated in this activity will cross at the pinhole.
Q1. What did you find out?
-Light from higher points on the object would travel in a straight line through the
pinhole, and end up low on the image.
- Light from lower points on the object would travel in a straight line through the
pinhole and end up high on the image.
CLASSWORK
Textbook:
- Read and make notes
- 4.1 (p.277 to 283)
- 4.2 (p.288 to 291)
- P. 283 “Check Learning” # 1-3
Complete handouts:
- Incandescence and Luminescence
- Light
- Reflect, Absorb, Transmit
QUIZ on WEDNESDAY