Transcript light - msvenables

A Brief Look at
LIGHT
Light usually travels
 only in a straight line.
 This is known as the
...
Law of Rectilinear
Propagation
Diagrams with Light
 are referred to as ray diagrams
 where a ray is a single path followed by
light
 and a beam is a ‘bundle’ of light rays.
When light strikes matter
– It can be affected in 3 different ways:
• Transmitted: light passes through a medium
– Ex. Windows
• Reflected: light bounces off an object
– Ex. Mirrors
• Absorbed: light disappears (or certain wavelengths)
– Green object  all wavelengths of light except green are
absorbed
Classifying Objects
 Objects may be classified based on how
well they transmit light:
 Transparent: transmits ALL light
 Opaque : transmits NO light
 Translucent: transmits SOME light
The Reflection of Light
 Regular Reflection: this is reflection of
light from smooth shiny surfaces.
Laws of Reflection
Normal
Incident
Ray
Angle of Angle of
Incidence Reflection
Reflected
Ray
90o
Mirror
Point of incidence
Laws of Reflection
Normal
Incident
Ray
First Law: The angle of
incidence is equal to the
angle of reflection
Angle of Angle of
Incidence Reflection
Mirror
Reflected
Ray
Laws of Reflection
Normal
Incident
Ray
Second Law: The incident
ray, reflected ray, and
normal all lie on the same
plane
Angle of Angle of
Incidence Reflection
Mirror
Reflected
Ray
Diffuse Reflection
 Many surfaces appear to be smooth, however when they
are viewed under a microscope it is clear they are not.
 Because of the uneven surface, the light rays are scattered
in many directions (diffused).
Diffuse Reflection
 Further examination of a irregular surface show
that they too obey the laws of reflection (ie. Angle
of incidence = angle of reflection).
Diffuse Reflection
 Most objects are made of rough surfaces
(and therefore scatter light); if this did not
happen, indoor lighting would not be
effective.
– ie. Walls, floors, ceilings, etc. scatter light in all
directions, making them visible.
Time to practice!
 Complete the worksheet “kinds of reflections”
 Complete the worksheet “regular and diffuse
reflection”
 Read text p.479-481 and p.484-486
 Do Questions: p. 481 #3, 5, p. 486 #1-5
Optical Images
 An image is the representation of an object
formed by the interaction of light rays.
 Characteristics (LOST):
Location: behind or in front of mirror
Orientation: vertical (upright or inverted)
lateral (left to right)
Size: bigger, smaller or same size as object
Type : Real – when the reflected rays converge in front
of the mirror to produce an image (can be seen on a screen)
or Virtual – when the reflected rays converge
behind the mirror (cannot be reflected onto a screen)
Images Formed in Plane Mirrors
Mirror
How do I see
an image of
the arrow??
Images Formed in Plane Mirrors
Mirror
Light from
the arrow hits
the mirror
Images Formed in Plane Mirrors
Mirror
..and is
reflected into
my eye
Images Formed in Plane Mirrors
Mirror
..and my brain ‘sees’ the
image where the light
appears to have come
from!
The
image!!
Characteristics of a PLANE MIRROR Image
 Characteristics in a plane mirror are always:
Location: behind the mirror the same
distance from the mirror as the object
Orientation: image is upright, and laterally
inverted
Size: same size as object
Type : virtual
(In you book it’s SALT (Size, Attitude, Location, Type))
Homework Time!
 Complete Worksheet “Plane Mirrors and their Images”
 Complete Worksheet “Drawing Images in a Plane
Mirror”
 Read pg. 488-492
 Do Questions pg. 493 #1-7, 9
 REMINDER: QUIZ on Tuesday!!! (electromagnetic
spectrum, sources of light, law of reflection and images
in a plane mirror)