Hbsc4403_teaching Science for Upper Secondary Iii_sept2012
-
Upload
mohd-zulkepli-zakaria -
Category
Documents
-
view
219 -
download
0
Transcript of Hbsc4403_teaching Science for Upper Secondary Iii_sept2012
FAKULTI PENDIDIKAN DAN BAHASA
PROGRAM SARJANA MUDA PENGAJARAN (SMP)
HBSC4403
TEACHING SCIENCE FOR UPPER SECONDARY III
SEPTEMBER 2012
______________________________________________________
NO. MATRIKULASI : 740603035469002
NO.KAD PENGENALAN : 740603035469
NO.TELEFON : 017-6621353
E-MEL : [email protected]
NAMA TUTOR : HUSSIN BIN MHD YUSUP
PUSAT PEMBELAJARAN :
PUSAT PEMBELAJARAN NEGERI SEMBILAN
1
CONTENTS
1.0 Introduction 3
2.0 Two phenomena related to refraction. 5
2.1 Real and apparent depth. 52.2 Mirages 6
3.0 Suggest how to explain the phenomena with teaching Strategies 7
4.0 A ray diagram for image formation from a convex lens 8
5.0 Explain the image formation of ONE selected optical device 11
6.0 State the application of the optical device selected 12
7.0 Conclusion 15
Reference
2
1.0 Introduction
Light is an electromagnetic wave. Visible light is the part of the electromagnetic
spectrum with wavelength between about 400 nm (ultraviolet) and 700 nm (red). Light, and all
electromagnetic waves, regardless of wavelength, travel at a speed c = 3 x 108 m/s in a vacuum.
In a transparent medium, light will travel slower than in a vacuum. Since light is a wave, it can
exhibit interference effects similar to what can be observed for waves on a string or sound
waves. Under certain conditions, light can also exhibit particle-like properties. Einstein
proposed that light consists of ‘quanta’, which are the smallest units of light. These quanta have
energy
E=hf and carry momentum
p= Ec=hf
c=h
λ ,
where f is the frequency, is the wavelength, and h = 6.63 x 10-34 Js is Planck’s constant.
Quanta have no rest mass (they are never at rest), but in certain experiments, they can collide
with electrons and transfer energy and momentum to the electrons, much like what would occur
for two particles with mass. In this chapter we will study what happens when a ray of light
strikes a surface or travels from one medium to another. We assume that light travels in a
straight line in a homogeneous medium.
When light passes from a less dense to a more dense substance, (for example passing
from air into water), the light is refracted or bent towards the normal.
3
The normal is a line perpendicular (forming a 90 degree angle) to the boundary between
the two substances. The bending occurs because light travels more slowly in a denser medium.
A demonstration of refraction can be conducted at home in a dark room. All that is
needed is a flashlight, a clear glass filled with water and a small mirror.
Figure adapted from Ahrens, 1994
Figure (a): Shine the light directly into the glass. If the light strikes the water straight on
(or parallel to the normal), no bending occurs and it simply passes directly into the water
undisturbed, leaving only a straight beam of light all the way to the bottom of the glass.
Figure (b): Shine the light into the glass at an angle. As the light enters the water, it is
refracted. Since the light is passing from air (less dense) into water (more dense), it is
bent towards the normal. The beam of light would appear to bend at the surface of the
water.
Figure (c): Place a mirror at the bottom of the glass of water and again shine the light
into the glass of water at an angle. As light initially enters the water, it is refracted as in
figure (b) and then reflected off the mirror (at the bottom of the glass). Upon exiting the
water, the light is bent away from the normal as it passes from water (more dense) and
into air (less dense). The light would leave the flashlight, bend at the surface of the water,
reflect off the mirror at the bottom of the glass and move towards the surface, where it
would bend outward at the same angle it bent in on the way in.
4
Apparent depth
Real depth
2.0 Two phenomena related to refraction.
2.1 Real and apparent depth.
The refraction of light at the surface of water makes ponds and swimming pools appear
shallower than they really are. A 1m deep pond would only appear to be 0.75 m deep when
viewed from directly above.(Figure D)
Figure D
When light emerges from glass or water into air it speeds up again. If it meets the glass-
air boundary at any angle other than 0o it will refract away from the normal. This is true for small
angles – something else happens when the angles get larger.
If you look at a stick that is poking into some water at an angle the stick looks bent
because of refraction. The bottom of the stick seems to be nearer the surface of the water than it
really is. It also explains why flat-based swimming pools appear to get shallower as you look
towards the end furthest from you.There is a connection between the real and apparent depths of
the water. It can be proved that:
5
Refractive index = real depth/apparent depth
Very hot air
cooler air
image
very cold air
warmer air
2.2 Mirages
A mirage occurs on very hot days when a layer of hot, low density air lies on the ground.
Light from the sky will be totally internally reflected at this layer and so you see what looks like
a pool of water - it’s actually a reflection of the sky. You may often see a shimmering layer of
reflecting air on a road on a very hot day – that is a mirage.
There is no sharp boundary between hot and cooler air and so the refraction is gradual.
Figure E
Mirages also occur in very cold countries. In the next diagram the mirage appears in the
sky and the polar bear seems to be flying upside down.
Figure F
6
.
3.0 Suggest how to explain the phenomena with teaching strategies.
3.1 Suggested Teaching Steps: Contextual Learning
a. Step One
Teacher discusses with the students their favourite drinks during a hot sunny day.
(Focus on the drinks in a transparent glass with a straw).
b. Step Two
Teacher demonstrates the typical phenomena of refraction using a glass of plain
water with a straw submerged in it and ask students to explain the condition of the straw
from their observation.
c. Step Three
Teacher asks the student to draw the phenomena in a two dimension diagram.
d. Step Four
Teacher gives feedback to the students’ response by giving the reason why the
bending of the straw occurred. In addition state clearly the media of different density
(water and glass), normal line, angle of incidence and angle of refraction based on
students drawn diagram as shown in the diagram.
e. Step Five
Once the students have mastered the concept of refraction well, you can gradually
introduce another everyday experience to students to gauge their understanding of the
concept. Introduce the scenario below to enhance the students’ understanding.
Aiman lives beside his friends’ fish pond and one day noticed a big patin fish in
the pond. He shoots the fish exactly at the angle of his apparent sight and was
unsuccessful in catching the fish. Ask the students to explain the reason by drawing the
scene.
7
f. Step Six
Teacher interacts with the students to share their understanding and finally
conclude the discussion using the diagram.
g. Step Seven
Teacher gives a few examples of refraction of light in student’s daily life
experiences.
Refraction phenomena
Fish in an aquarium looks bigger and closer when seeing from the side. (Real and apparent depth)
Immerse your hand in a plastic pail containing full of water. The hand will look bigger and closer.
A 50 cent coin under a block of glass seeing bigger and closer when seeing from top of the glass.
h. Step Eight (Conclusion)
Teacher concludes that refraction required the light to move between two
different media of different density and refractive index.
4.0 A ray diagram for image formation from a convex lens.
A converging lens is also called a convex lens because it is thicker at the centre
than at the edges. As parallel light rays travel through a convex lens, they are refracted
toward the principal axis. This causes the rays to move toward each other. The light rays
cross at the focal point of the lens. Converging lenses are often used as magnifying
glasses (Figure H).
Figure H
Convex lenses are useful because they can form a real image on a screen. For
8
example, the light rays coming from one point on the flame in Figure 11.57 diverge and
strike the lens at different places. However, the lens redirects all those rays so that they
converge at a single point. The screen must be placed so that the light rays strike it exactly
as they converge. This way, when the light rays reflect off the screen, they are coming from
a single point, just like when they originally left a single point on the candle.
At the same time, the lens must also redirect all light rays that come from a point at
the base of the candle and send them to a single point on the screen. The rays then reflect off
the screen in all directions, just like when the light rays from the base of the candle left the
candle. When the rays from every point on the candle are sent to the screen, a complete
image is formed. You can compare the type of image formed at different distances as well as
some of the uses of convex lenses in Figure I.
screen
candle
image (upside down)
Figure I. As you can see in this illustration, there is one drawback to convex lenses. The image is upside down!
Images Formed by Convex Lenses
9
Distance of Object Type of Image How Image Is Used Ray Diagramfrom Lens Formed
More than two focal Smaller, A camera uses thislengths inverted, distance to make
real smaller images of anobject.
Between one and Larger, Photographic imagetwo focal lengths inverted, enlargers, slide
real projectors, and movieobjectprojectors use this
distance. Fimage
Less than one focal Larger, Magnifying glasses imagelength away upright, and reading glasses
virtual make use of thisdistance.
objectF
4.1 Drawing a Convex Lens Ray DiagramYou can follow the steps in Figure J to draw a ray diagram of a convex lens.
1. The first ray of a convex lens ray diagram travels from the tip of the object parallel to the
principal axis (ray 1). When it emerges from the lens, it passes through the principal
focus.
2. The second ray travels from the tip of the object through the optical centre of the lens
and is not refracted (ray 2).
3. Draw the real image where the rays appear to intersect.
object ray 1
ray 2F image
Figure J Convex lens ray diagram
5.0 Explain the image formation of ONE selected optical device.
10
5.1 A microscope
A basic microscope is made up of two converging lenses. One reason for using
two lenses rather than just one is that it's easier to get higher magnification. If you want
an overall magnification of 35, for instance, you can use one lens to magnify by a factor
of 5, and the second by a factor of 7. This is generally easier to do than to get
magnification by a factor of 35 out of a single lens.
A microscope arrangement is shown below, along with the ray diagram showing
how the first lens creates a real image. This image is the object for the second lens, and
the image created by the second lens is the one you'd see when you looked through the
microscope.
Note that the final image is virtual, and is inverted compared to the original object. This
is true for many types of microscopes and telescopes, that the image produced is inverted
compared to the object.
5.1.1 An example using the microscope
Let's use the ray diagram for the microscope and work out a numerical example.
The parameters we need to specify are:
do=7.0mm ho=1.0mm
f o=4.5mm f e=10.0mm
Distance between the two lenses = 20mm
To work out the image distance for the image formed by the objective lens, use the lens
equation, rearranged to:
11
The magnification of the image in the objective lens is:
So the height of the image is -1.8 x 1.0 = -1.8 mm.
This image is the object for the second lens, and the object distance has to be calculated:
The image, virtual in this case, is located at a distance of:
The magnification for the eyepiece is:
So the height of the final image is -1.8 mm x 3.85 = -6.9 mm.
The overall magnification of the two lens system is:
This is equal to the final height divided by the height of the object, as it should be. Note
that, applying the sign conventions, the final image is virtual, and inverted compared to
the object. This is consistent with the ray diagram.
6.0 State the application of the optical device selected.
Optical microscopes use visible light and a system of lenses to magnify small samples
that are usually un-seen to the bare eye. The optical microscope is the first, oldest and simples
type of microscope as opposed to the much more advanced electronic microscope. The first
optical microscopes were created in the 18th century. Due to it's compact sizes, simplicity and
relatively low price, the optical microscope is very popular, and can be found in use in many
areas of biology. Optical microscopes mostly magnify objects for up to 1500 times.
The first optical microscopes were structured in a way that is called "the simple
microscope". This structure utilizes only one pair of lenses to create a magnified image of the
sample. Today, the simple structure is in use only in the magnifying glass, hand lens and the
12
loupe.
The more advances optical microscopes, and the ones that are popular today, are what's
called "compound optical microscopes". These microscopes use a system of many lenses, in
order to "compound" and multiply the magnification, and therefore maximize it. The two main
lens systems in an optical microscope are the objective lens (near the examined object), and the
eyepiece lens (up near the eye of the scientist). Modern optical microscopes use multiple lenses
both in the objective part as well as the eyepiece part.
The old optical microscopes also used a mirror to provide illumination below the object.
The modern optical microscopes use a strong lamp to provide constant and strong illumination.
So what are optical microscopes used for now a days?The main uses of compound optical
microscopes include:
The examining small pieces of material, or even a smear or a squash preparation. This is
due to the fact that the optical microscope uses light to pass beneath the object and enter the
lenses. That's why the item is better be half-transparent. In other uses the optical microscope may
be used to examine metal samples, in order to study the metal's structure. At low power,
microscopes can be used to examine small living animals and plants. At high power, they can be
used to examine bacteria.
It is important to note that the vast advancement in medicinal fields and biology in
general, is owed to a large extent, to the invention of the optical microscopes. For example, the
way the blood flows in our body was not fully understood until the microscope made in possible
to examine small blood vessels behavior.
6.1 Practical Applications of Electron- and Ion-Beam Microscope.
Electron microscopes and ion beam microscopes are both amazing and incredibly
complex scientific instruments used by research laboratories, universities, nanotechnology
centers, and companies worldwide. Although few of us will ever own or use an electron
microscope, their impact is pervasive, impacting our lives in a variety of ways, from the clothes
we wear, to the tools and devices we use, and the food we eat. The applications for these
instruments are diverse, ranging from particle analysis to material characterization to industrial
failure analysis and process control. In the electronics industry, for example, semiconductor and
13
electronics manufacturers use specialized microscopes for high resolution imaging and analysis
required to develop and control the manufacturing process.
Companies worldwide use electron microscopes in a variety of industrial applications
including aeronautics, automotive manufacturing, clothing and apparel, machining,
pharmacology, and many more. Forensic science, the application of science to law, is one
example made popular by the television show "CSI" and others. Microscopic analysis of gunshot
residue, blood samples, or clothing fibers to help solve crime is common on TV, and in real life.
In life sciences, electron microscopes are being used to explore the molecular
mechanisms of disease, to visualize the 3D architecture of tissues and cells, to unambiguously
determine the conformation of flexible protein structures and complexes, and to observe
individual viruses and macromolecular complexes in their natural biological context.
In natural resources, the ability to characterize and analyze organic materials is critical
for mining companies to analyze millions of micro-scale features in an automated, objective,
quantitative, and rapid manner. In oil and gas exploration, similar analyses provide quantitative
lithotype and porosity characteristics of reservoir, seal, and source rocks. The results enhance
and validate seismic, wireline, and mud logs, providing input into geological models and
reducing risk in exploration and extraction. You can learn more about applications in natural
resources by visiting our dedicated natural resources website located at fei-natural-
resources.com.
Researchers worldwide are using electron microscopes in the pursuit of a deeper
understanding of the structure-property-function relationships in a wide range of materials and
processes such as next generation fuel cell and solar cell technologies, catalyst activity and
chemical selectivity, energy-efficient solid-state lighting, and lighter, stronger, and safer
materials.
7.0 Conclusion
14
From this we should have gathered that refraction is the bending of light as it enters a
new medium.The normal is an imaginary line perpendicular to the boundary.The angle of
incidence is measured from the normal to the incident ray.The angle of refraction is measured
from the normal to the refracted ray.If light enters a more optically dense material, the speed
decreases and the light bends towards the normal.If light enters a less optically dense material,
the speed increases and the light bends away from the normal.The angle of incidence that results
in an angle of refraction of 90 degrees is call the critical angle.If the angle of incidence is greater
than the critical angle total internal reflection occurs.
References
15
Dr Mohd Ali Samsudin,Assoc Prof Dr Syarifah Norhaidah Syed Idros,Tan Kee Yean and
Haji Norawi Ali (2011). Hbsc4403 Teaching Science For Upper Secondary III, Meteor Doc.
Sdn.Bhd .Seri Kembangan.
http://homepage.usask.ca/~dln136/refraction/pages/first_process.html
http://www.physicsclassroom.com/Class/refrn/U14L1b.cfm
http://www.curriculumbits.com/prodimages/details/physics/refraction.html
http://www.sd22.bc.ca/~tnenzen/Physics_11/Handouts/080116-Lab-Lenses.pdf
http://courses.ncssm.edu/apb11/labs/L18/L18_focal_length.htm
http://www.mscd.edu/~cfmsaee/PDFs/LENS
http://www.thealy.com/LCPhysics/notes/lenses.htm
16