•
•
•
•
•
•
•
•
•
•
ELECTROMAGNETIC
WAVES
Name given to a range of waves having different wavelengths, frequencies
and energies but some common properties
All are propagated by varying electric and magnetic fields which oscillate
at right angles to one another and also to the direction of propagation of
the wave
All travel with the same constant speed in air or a vacuum…the speed of
light…3.0x108 ms-1
All are unaffected by external electric and magnetic fields
All are transverse waves
All can undergo reflection, refraction, diffraction and interference
All travel in straight lines in a vacuum or air or other medium
All can be plane polarized
All are progressive waves but can produce stationary waves under suitable
circumstances
The intensity of each varies inversely as the square of the linear distance
from a point source
Electromagnetic spectrum is divided into the following range
with specific range of 300nm (violet light) to 750nm (red light)
Light has a wave-particle nature:
Wave nature supported by the young double slit experiment that light can be
Diffracted and interference can occur and
The Photoelectric effect ( instantaneous emission of electrons from the surfaces of
certain material when exposed to E.M. radiation above a certain frequency
Light
Is a form of energy that has a
particle and wave nature
Light travels in straight lines
• Its travel is represented by a ray
• A ray is a straight line a with an arrow showing
the direction of travel
A ray
A group of rays represent a beam of light
A beam
There are three main types of beams of light:
• Parallel beams
• Convergent beams
• Divergent beams
Use your dictionary to write down the meanings
of
1) Parallel ______________________________
2) Convergent ___________________________
3) Divergent ____________________________
• A torch light creates a divergent beam, attempt to draw a beam of
light from the torch light to show a divergent beam using the
diagram below.
Example:
Is it?
or
or
• Headlights on a car creates parallel beams, attempt to draw a beam
of light to show a parallel beam using the diagram below
• A magnifying glass creates convergent beams, attempt to draw a
beam of light to show a convergent beam using the diagram below
Luminous versus non-luminous
• If you are given the definition that luminous
objects produce it own light and nonluminous objects reflect light, make a list of at
least five objects that are luminous and nonluminous objects
Luminous objects
Non luminous objects
And you are given the definition that:
• Transparent objects allow all light to pas through it
• Translucent objects allow some light to pass through
it
• Opaque objects do not allow any light to pass
through it
• Complete the table below with at least five items you
see daily
Transparent
objects
Translucent
Opaque
Glass
Frosted glass
A wall
SHADOWS
Are formed when an opaque object is
placed in front of the path of light.
Shadows can be formed using
• Using a point source – which is a small light
source such as a torch light
• Or an extended source – which is a large light
source such as the sun
Solar eclipse
• When the moon passes between the sun and
the Earth
• The moon fully or partially covers the view of
the sun from the Earth
• The partially covered view is the area of the
penumbra
• The fully covered view is the area of the
umbra.
TO DO: Label on the diagram where you would be
if you were seeing an Annular eclipse
Total Solar Eclipse:
• The observer is inside the
Moon's umbra.
• The Moon completely
covers the Sun.
Partial Solar Eclipse:
• The observer is inside the
Moon's penumbra.
• Only see part of the Sun
covered by the Moon.
Annular Eclipse:
• The Moon is at or near
apogee, and so is too
small to cover the Sun.
• The Moon's umbra does
not touch the Earth, so
observer's in the shadow
path see the Sun as a ring
("annulus")
Lunar Eclipse
A lunar eclipse occurs
when the moon passes
behind the Earth and is
blocked by Earth (the
Earth acts as the
opaque object)
• TO DO: Draw a diagram
of the Sun, Earth and
Moon in a lunar eclipse
position