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 : mzul@ymail.com.my

NAMA TUTOR : HUSSIN BIN MHD YUSUP

PUSAT PEMBELAJARAN :

PUSAT PEMBELAJARAN NEGERI SEMBILAN

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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

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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.

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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.

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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:

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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

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.

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.

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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

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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

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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.

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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:

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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

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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

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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

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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

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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

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