Download File - Ms. D. Science CGPA

Waves and Light
Table of Contents
Reflection and Mirrors
9.2
Ms. De Los Rios
7th Grade
Waves of the Electromagnetic Spectrum
Types of Waves
The electromagnetic spectrum includes many kinds
of waves. Identify each kind of wave on the electromagnetic spectrum.
What is the name of the highest energy waves?
Vocabulary 9.2
1. Rays- A straight line used to represent a light wave.
2. Regular Reflection- A reflection that occurs when parallel rays of light
hit a smooth surface and all reflect at the same angle.
3. Image- a copy of an object formed by refracted rays of light.
4. Diffuse Reflection- Reflection that occurs when a parallel rays of light
hit an uneven surface and all reflect at different angles.
5. Plane Mirror- A flat mirror that produces an upright, virtual image the
same size as the object.
6. Virtual Image- An upright image formed where rays of light appear to
come from.
Vocabulary 9.2
7. Concave Mirror- A mirror with a surface that curves
inward.
8. Optical Axis- An imaginary line that divides a mirror in half.
9. Focal Point- The point at which light rays parallel to the optical
axis meet, or appear to meet, after being reflected (or
refracted) by a mirror or a lens.
10. Real Image- An upside-down image formed where rays of light
meet.
11. Convex Mirror- A mirror with a surface that curves
outward.
What is a scientific law?
A statement that describes what a
scientists expect to happen
every time under a
particular set of conditions.
Scientific Theory?
A well-tested
explanation for a wide
range of observations or
experimental results.
(NOT PROVEN)
Law of Reflection
Law of Reflection states: The Angle of reflection equals the
angle of incidence.
outgoing or reflected
Incoming/
incident ray
•
Reflection involves two rays - an incoming or incident ray and an outgoing or reflected
ray. In the figure 1(above), I’ve used a single line to illustrate a light ray reflected from the
surface.
•
The law of reflection requires that two rays are at identical angles but on opposite
sides of the normal which is an imaginary line (dashed in Fig. 1) at right angles to the
mirror located at the point where the rays meet.
I’ve shown in Fig. 1, that the angles of incidence i and reflection i' are equal by joining the two
angles with an equal sign.
What are the Kinds of Reflection? Pg. 322
To understand how light reflects:
• think of light waves as straight lines called rays, and a
surface reflects light.
•
Light obeys the law of reflection that states the angle of
reflection equals the angle of incidence/incoming.
The two ways in which a surface can reflect light;
1.
Regular reflection- (smooth surface)
2.
diffuse reflection- (surface uneven)
What are the Kinds of Reflection? Pg. 323
The Two Ways in Which a Surface can Reflect Light
Regular Reflection occurs when
parallel rays of light hit a smooth
surface. You see a clear image. An
image is a copy of the object
formed by reflected or refracted
rays of light.
Diffuse reflection occurs when
parallel rays of light hit an uneven
surface. You either don’t see an
image or the image is not clear.
Most objects reflect light diffusely.
Reflection and Mirrors pg. 323
Diffuse and Regular Reflection
Which kind of reflection occurs on each surface?
What Types of Images Do Mirrors Produce?
Pg.324
A plane mirror is a flat sheet of glass that has a
smooth, silver-colored coating on one side.
Light strikes the mirror the coating reflects the light
The image you see in a plane mirror is a virtual
image— an upright image that forms where light
seems to come from.
A plane mirror produces a virtual image that is:
• Upright
• Same size as the object
• The image, the left and right of the object are
reversed.
What Types of Images Do Mirrors Produce?
A concave mirror has a
surface that curves inward,
like the inside of a bowl.
• A concave mirror can reflect
rays of light parallel to the
optical axis so that they meet
at a point.
• The optical axis is an
imaginary line that divides a
mirror in half.
• The point at which rays
meet is the focal point.
Optical Axis
Pg.324
Reflection and Mirrors
Concave Mirror
A concave mirror reflects
rays of light parallel to
the optical axis back
through the focal point.
(right hand index & thumb)
What Types of Images Do Mirrors Produce?
Concave mirrors can produce two types of images:
Pg.325
real
virtual images.
Real Image if:
• If the object is farther away from the mirror than the focal point.
A real image forms when:
• light rays actually meet.
A real image can be projected on a surface.
• Real images are upside down.
A real image size may be:
• smaller, larger, or the same size as the object.
Virtual Image if:
• If an object is between the mirror and the focal point
Virtual Image size:
• the reflected rays form a virtual image that is larger than the object.
Reflection and Mirrors
Real and Virtual Images
The figures show how a concave
mirror can produce both real and
virtual images.
What Types of Images Do Mirrors Produce?
Pg.325
A convex mirror has a
surface that curves outward.
• When parallel rays of light are
reflected by a convex mirror, the
rays spread out but appear to
come from a focal point behind
the mirror.
• A convex mirror produces a
virtual image
•
The virtual image is always
smaller than the object.
(left hand index & thumb)
Reflection and Mirrors
Convex Mirror
Light rays parallel to the optical axis reflect as if they came from the
focal point behind a convex mirror. Where do two reflected rays
intersect behind the mirror?
Reflection and Mirrors
Different Types of Images Formed by Mirrors
Compare and Contrast The Shape of a Convex and
Concave Mirror
Convex Mirror
Concave Mirror
Resources
http://www.optics4kids.org/home/teachersparents/articles/the-reflection-of-light/
Law of Reflection Tutorial
http://cnx.org/content/m42456/latest/
Reflection of Light Java
http://micro.magnet.fsu.edu/primer/java/scienceopticsu/reflection/reflectionangles/index.html
Waves activity
Seismic waves travel through the Earth. There are two types - P waves and S waves. Find out more in this activity.
http://www.bbc.co.uk/schools/gcsebitesize/science/edexcel_pre_2011/waves/soundultrasoundandseismicwavesact.sht
ml
Optics Workbench
http://www.iknowthat.com/com/OpticsWorkbench?Benchmode=True