2018 h2 physics light polarisation and malus’ law · 2019-01-17 · 2018 h2 physics light...

2018 H2 Physics Light Polarisation and Malus’ Law

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Experiment 1807 (Part A) Experimental Planning with Inquiry Based Learning (IBL)

Light Polarisation and Malus’ Law

Name : ……………………………………………………..… CG : ……… Date : …..………

In this guided approach to Inquiry Based Learning (IBL), we will explore the nature of light in particular

its behaviours both qualitatively and quantitatively according to Malus’ Law on light polarisation.

The aim of this exercise is for students to develop a scientific sense of exploration and experimentation while making connection to their prior knowledge on light waves. Here, practical work aims to complements theory and hopefully through these series of activities, students can be led to manifest evidences of the 5 E’s -

1. Engagement – to pose or raise questions about certain phenomena 2. Exploration – to develop ways to test predictions and record observations in a controlled way 3. Explanation – to offer possible solutions and to question any assumptions 4. Elaboration – to draw reasonable conclusions from evidence gathered 5. Evaluation – to reflect and extend one’s thinking

This IBL exercise will be conducted as pair-work (trio if the class size is an odd number) to facilitate discussion and exchanges of ideas. Part A is to help you consolidate your prior knowledge (ie the theory bit) while part B (ie the practical bit) is to train you for H2 Physics Paper 4 which has an open ended question that test you on your planning skills.

Having a good head knowledge of the topic (e.g. light polarisation) will invariably help you make sense of the various stages when planning an investigation. Your learning skills include developing good observational and analytical skills while at the same time to be able to evaluate your own proposal so as to generate reliable and accurate data to support your claim and draw meaningful conclusions.

We will use the S.T.A.R. process as an authentic application to IBL.

Scenario analysis Students are given authentic scenarios or problems which they need to analyse and identify the key learning issues.

Team inquiry Working in teams, students go through the process of collaborative inquiry, communication and problem solving as imbued in 21st century competencies which MOE advocates.

Application Students apply what they have learned, and propose explanations or solutions to address the scenario in an authentic way.

Reflection Teacher and students evaluate and discuss what has been learned. Students reflect on their learning and on the learning process. It is important for students to learn to self-regulate when they review their strengths, weaknesses, learning, and study strategies. It can help students to have a greater sense of ownership of their learning.

HOME > PEDAGOGICAL PRACTICES > LESSON ENACTMENT > ACTIVATING PRIOR KNOWLEDGE > SCENARIO ANALYSIS, TEAM INQUIRY, APPLICATION AND REFLECTION (STAR)

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https://opal.moe.edu.sg/stp/pedagogical-practices/lesson-enactment

https://opal.moe.edu.sg/stp/pedagogical-practices/lesson-enactment/activating-prior-knowledge


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Objectives

Pre-Lesson Preparation

Read through the content on pages 3-5 as well as your lecture notes to review your prior knowledge on the topic. It will help to solidify your learning.

Experiment 1807 - Part A (To do during tutorial – 50 min)

(1) To consolidate prior knowledge on the topic of light polarisation. Aim :

To learn about light polarisation and Malus’ Law through inquiry.

(2) To show that light is a transverse wave by way of polarisation.

(3) To verify that when a beam of unpolarised light passes through a polariser, the light intensity is halved.

After acquiring a good understanding of the topic (Part A), we can then proceed to Part B which is to

design and carry out experiments related to it. Through this experience, you will learn to look critically

at your design and maybe spot any flaws in it so as to improve on the reliability of your experimental

data.

Experiment 1807 - Part B (To do during practical – 100 min)

In an attempt to verify Malus’ Law I2 = I

1 cos2, we will be using Light

Dependent Resistor (LDR) as a proxy (substitute) indicator for light intensity. Assuming that the resistance R of the LDR is inversely proportional to the

emergent light intensity I shining on the LDR surface, we are going to design an experiment to verify the relationship between resistance R of the LDR and θ through the relation

2

0

1 1cos

R R

where Ro is the resistance of the LDR when the axes of the two polarisers

are parallel and is the angle between the polarising axis of the polarisers.

Aim:

To learn the skills needed to plan and design experiments.


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Objective 1 To consolidate prior knowledge on the topic of light polarisation.

Think-Pair-Share (5 min)

List down what you know thus far about the nature or properties of light.

Properties of (visible) light. Give relevant evidence/s (if possible) to support this claim.

What is the antithesis (ie the same evidence also negate other properties).

It is a wave. Effects of interference and diffraction shows light has wave properties.

Light is “not particle’? (to be done later under QP)

It can transfer energy from one place to another.

Speed is 3×108 m s-1

Example: The sun’s rays received by solar cells can generate electricity.

Mobile phones can receive energy transmitted by radio waves.

Light is not a stationary wave? It is possible to make light a stationary wave. Depends on the conditions and context.

It carries electric and magnetic fields. It is a type of electromagnetic wave.

Food can be heated in a microwave oven due to dielectric oscillation when subjected to microwaves.

It is not a mechanical wave as it does not require a medium to be transmitted.

It is transverse wave in that the oscillation is perpendicular to the direction of energy transfer.

Because can be polarised it is a transverse wave.

It is not a longitudinal wave.

Can we generalise the above properties which are for light rays to other types of waves in the electromagnetic spectrum, such as radio, microwaves, IR, UV, X-ray?

Yes, because they are electromagnetic waves, they share similar properties except they vary in terms of energy and wavelength.

So if light can be polarised, does that mean that other electromagnetic waves can be polarised also?

Yes, other EM waves can be polarised (i.e. made to oscillate in a single plane) but the type of polarisers used may vary. For example, polarised radio waves can be transmitted by a dipole antenna, property of polarisation for microwaves can be demonstrated using an iron grill.

To summarise the properties of light, let’s view the following video

https://www.youtube.com/watch?v=fsrq4RTHJvc Hewitt-Drew-it! PHYSICS 114. Polarization of Light (play till 2min 50s)

https://www.youtube.com/watch?v=fsrq4RTHJvc


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So let’s now turn our attention to one property - light polarisation and what it is.

Consolidating Prior Knowledge

Light is a form of propagating electromagnetic radiation or waves which consist of mutually perpendicular electric (E-) and magnetic (B-) fields components.

Because the variations of these fields occur perpendicular to the wave velocity, light is a transverse wave. The evidence that supports this assertion is a phenomenon called polarisation.

Polarisation is the property that applies to transverse waves

that specifies that the orientation of the oscillations is along

a plane perpendicular to the direction of energy transfer of

the wave.

The polarisation axis by convention is taken to be the same as the E-field component because charged particles oscillate parallel to the E-field and perpendicular to the B-field. So corresponding

to the EM wave shown in Fig. 1, the polarising axis is depicted as a vertical line. Fig. 2b

Unpolarised light Polarised light

For unpolarised light, the waves oscillate in a multitude of planes while being perpendicular to

the direction of wave propagation.

a.k.a. linearly polarised or plane polarised, the wave oscillate in a single plane perpendicular

to the direction of wave propagation.

or

multiple planes simplified version

Fig. 2a

x-component is absent, Ax = 0

Fig. 2b

Explain the significance of having equal lengths for the vertical (Ay) and horizontal (Ax) amplitudes

as depicted in Fig. 2a.

This concept of unpolarized light is rather difficult to visualize. In general, it is helpful to picture unpolarized light as a wave that has an average of half its vibrations in a horizontal plane and half of its vibrations in a vertical plane.

It shows that the light ray is randomly (or equally) distributed in all

directions of oscillations.

If the x amplitude is larger than the y-amplitude, it would suggest that

the light waves are more dominant in the x- direction than the y-

direction. This is a.k.a. being partially polarised.

Ay

Ax

Ay


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1. Passing an unpolarised beam of light through one polarising filter.

Fig. 3

The slender arrow represents a ray of unpolarised light. The bold arrows represent the direction of polarization of the individual waves composing the ray. Since the light is unpolarised, the arrows point in all directions. After passing through the polariser, the emergent light is plane polarised (or linearly polarised). The plane for the polarised emergent ray follows after the polarising axis of the

polarising filter.

intensity amplitude direction

Incident unpolarised light Io

A in y direction

A in x direction

Unpolarised.

After passing through the polariser

I1 =

1

2I

o

Half-Rule

A in y direction only

Plane of polarised wave is parallel to the polarising axis of the polariser.

Think (recall prior

knowledge) What do you know about this topic?

Puzzle (making the connection

between results and theory, putting the pieces together)

Explore / Explain (Venturing an explanation)

Light is an EM wave.

Why is the light intensity halved after passing through the polariser? What happens to the energy that was received by the polariser if the emergent light intensity is half of the initial?

Passing a beam of unpolarised light through an ideal vertical polariser causes the perpendicular components to be absorbed (Ax = 0). Thus, the transmitted light has amplitude Ay only and that means only half of the initial intensity is transmitted. The other half of the energy has been absorbed by the long chain molecules contained in the polariser. The electrons move along the length of the long molecules in response to the oscillating electric field whose plane is parallel to the rows of molecules in the polariser. The energy absorbed is ultimately dissipated as heat.

Further viewing and understanding of the ‘Half Rule’.

https://www.youtube.com/watch?v=BqTy-T_jpzA&feature=youtu.be

Ay

Ax

Ay

Io

I1 = Io /2

Think like a

scientist!

https://www.youtube.com/watch?v=BqTy-T_jpzA&feature=youtu.be


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2. Passing an unpolarised beam of light through two polarising filters in succession.

The first filter is simply called the polariser

because after unpolarised light (of intensity Io) passes through it, the transmitted light will be plane

polarised and its intensity I1 =

1

2Io (Half-Rule).

When this plane polarized light is incident onto a second polariser, the intensity I

2 of the light

transmitted across both polarisers in succession will vary when the polarising axis of the second polariser is rotated relative to the first. It is this variation in transmitted light intensity which we wish to ‘analyse’ and so we call the second polariser, the analyser.

Malus’ Law states that when a polarizer is placed in the path of a polarized beam of light, the intensity

I2 of the emergent light is given by

I2 = I 1 cos2 θ where I

1 is the initial intensity of incident polarised light

θ is the angle between the incident light polarization

direction and the polarising axis of the analyser.

Malus’ law on the variation intensity of the emergent wave with the relative angle

Note that the polarised plane of the emergent light follows after the polarising axis of the last polariser from which the light emerged (in this case the analyser).

Incident unpolarised light

After passing the polariser (express in terms of the value in the second column)

After passing the analyser (express in terms of the value in the

second column and )

intensity

Io I

1 =

1

2 I

o

(half-rule)

I2 = I

1 cos2 θ

= 1

2 I

o cos2 θ

amplitude Ay = A

Ax = A

Ay = A

Ax = 0

A2 = A cosθ

direction unpolarised polarised in y-direction plane polarised in θ direction

0o 90o 180o 270o 360o

Intensity I2 of emergent light I

1

0


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Optional Exercise: Refer to Appendix A - How does a polariser work?

Objective 2

To show that light is a transverse wave by way of polarisation.

View the light source (e.g. torchlight) through a pair of polarisers placed one after another. The polariser has its polarising axis fixed in the vertical direction. The analyser’s polarising axis is rotated gradually from 0o (vertical) to 90o(horizontal).

Predict Write down what you expect to see.

Observe Write down your actual observation here.

Explain What does this observation suggest about the property of light?

The emergent light will vary in intensity when one polaroid is rotated relative to the other.

Ideal result The light intensity alternates from maximum to zero through intervals of 90o angular displacement between the two polaroids. In practice The light intensity varies with the rotation but it does not cancel out completely to yield total darkness even when the polarising axes are perpendicular.

The fact that light intensity changes with different orientation of the polaroids suggest that light is a transverse wave and not a longitudinal wave. The polaroid may not be functioning fully (or ideally) as an absorbent polaroid as the layer is too thin to completely absorb the component E-field in that direction. Another possibility is that the polariod may have lost some of its polarising ability due to damage brought about by prolonged exposure to the high light intensity which can cause the chemical composite in the polarisers to be denatured. So complete cancellation of light was not achieved and the transmitted light is partially polarised.

Based on your observation above, what can you conclude about the nature of light?

…………………………………………………………………………………………………

…………………………………………………………………………………………………

The fact that light can be polarised and blocked when the polarising axis are perpendicular to

each other shows that it is a transverse wave and not a longitudinal wave.

Think like a

scientist!


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Objective 3

To verify that when unpolarised light ray passes through a polariser, the light intensity is halved.

Procedure: 1. Download a free lightmeter app. (e.g. Galactica, LUX Lightmeter) onto your handphone. Use

the app. to record the light intensity.

2. Direct your handphone to a light source (eg light bulb, torchlight). The illumination is recorded in ‘lux’. Record the initial reading.

3. Place one polaroid over your HP’s camera lens or sensor. Record the new illumination and complete the tables below.

List some factors you had to control (or keep constant) so that the results are reliable?

Results

Light

source

Initial intensity

(without polaroid)

Io / lux

Final Intensity

(with polaroid in front)

I1 / lux

Percentage

reduction

𝐼𝑜 − 𝐼1

𝐼0

%

Any significant reduction when the polaroid

was rotated?

Predict Write down what you expect to see.


Explain

Sample

The light intensity would be reduced to half when a polaroid is placed in front

of the light source.

Rotating to the polaroid will not have any effect on

the transmitted intensity.

Ideal result

The light intensity is approximately reduced to half. Rotating the polaroid does not cause the illumination to vary.

In practice The light intensity was not reduced to

half. Rotating the polaroid may cause the illumination to vary.

The light source truly emits unpolarised light because the intensity of the emergent light is approximately the same in any direction of the polaroid.

Some light sources are not completely random in terms of

their polarising axis as the percentage reduction was not 50% as predicted in theory.

The ambient light is not randomly polarised to begin with (eg light from mobile phone screen). This was evident when the light intensity varies with different orientation of the polaroid.

View this to summarise concepts. https://www.youtube.com/watch?v=K1j9J1yL8fU 8 Malus' Law (fr. University of New South Waves, Australia)

1. The separation between the light source and the lightmeter is fixed. Camera must be

pointing the same direction at all times.

2. It would be better to carry out the experiment in a darkroom so that the illumination

is due to only one light source.

3. The lightmeter is ‘cupped’ to shield it from light coming from the sides. This is to

ensure that only the light from the polariser is received by the lightmeter.

Think like a

scientist!

Do the “Exit Pass” and return to your tutor.

You have 10 mins to complete and submit.

https://www.youtube.com/watch?v=K1j9J1yL8fU


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Appendix A

How does a polariser work?

To answer this question, let’s consider firstly the polarisation of microwaves (also an EM wave) using

an iron grill.

The above experimental set-up uses an iron grill placed between a microwave transmitter and a

receiver. Recall that the iron grill is made up of metallic conductors with many free electrons in them.

1. When the iron grill is orientated vertically, the receiver register minimum or zero reading.

Explain why this is so?

Think (recall prior

knowledge) What do you know about

this topic?



Explore / Explain Venturing an explanation.

Hint : Microwave is an EM wave. The iron grill has free electrons. How do they interact?

The receiver detects little or no microwaves. Why?

The free electrons are able to oscillate about the length of the iron grill in sympathy with the incident E-field. Since the microwave oscillates in a plane parallel to the iron grill, much of its energy is absorbed and dissipated. Thus, the receiver does not register much of the microwave.

2. When the iron grill is orientated horizontally, the receiver register maximum reading.

Explain why this is so?

Think (recall prior

knowledge) What do you know about

this topic?



Explore / Explain Venturing an explanation.

Hint : Microwave is an EM wave. The iron grill has free electrons.

The receiver detects a large value. Why?

When the iron grill is placed horizontally, the oscillations of the free electrons are constraint by the width of the grill which is narrow in the direction of the E-field. So, the incoming microwave is generally unaffected and much of it passes through the grill.

Summary

Orientation of incident microwave from transmitter

Orientation of iron grill

Polarising axis of iron grill (state the direction)

Signal at receiver (max. / min.)

vertical vertical horizontal minimum

vertical horizontal vertical maximum

Note that the polarising axis of the iron grill is perpendicular to the direction of the grill.

The microwave (3 cm)

transmitter emits a

plane polarised wave

in the vertical

direction.

Microwave

receiver

Iron grill


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Light may be polarized by passing it through a sheet of commercial material called Polaroid, invented

by E.H. Land in 1938. A sheet of Polaroid transmits only the component of light polarized along a

particular direction and absorbs the component perpendicular to that direction.

The optical or light polariser functions similarly on an atomic scale to the iron grill polariser. The light

polariser is made of long microscopic herapathite crystals suspended in a polyvinyl alcohol (PVA)

plastic sheet. Stretching the sheet during the manufacture causes the PVA chains to align in one

particular direction. The valence electrons from the iodine dopant are able to move linearly along the

polymer chains but not transverse to them. So incident light polarized parallel to the chains is

absorbed by the sheet; light polarized perpendicularly to the chains is transmitted.

Long molecules are aligned perpendicular to the axis

of a polarizing filter. The component of the electric field

in an EM wave perpendicular to these molecules

passes through the filter, while the component parallel

to the molecules is absorbed.

An electron in a long molecule oscillating parallel to the

molecule. The oscillation of the electron absorbs energy

and reduces the intensity of the component of the EM wave

that is parallel to the molecule.

Thus, the axis of the polarizing filter is perpendicular to the

length of the molecule.

Consider an unpolarised light beam in the z direction incident on a Polaroid which has its transmission

axis in the y direction. On the average, half of the incident light has its polarization axis in the y

direction and half in the x direction. Thus, half the intensity is transmitted, and the transmitted light is

linearly polarized in the y direction.

End of Expt 1807 - Part A


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Experiment 1807 (Part B) Experimental Planning with Inquiry Based Learning (IBL)

Light Polarisation and Malus’ Law

Name : ……………………………………………………..… CG : ……… Date : …..………

Typical Paper 4 Exam Planning Question

Actual time given to complete this exam question is 30 min.

The intensity I of the emergent light after passing through two polarisers depends on the angle θ

between the two polarising axis of the polarisers.

The variation between I and θ is thought to be related by

I = Io cos2 θ

where Io is the intensity of the light when the axes of the two polarisers are parallel.

A student wishes to use a Light Dependent Resistor (LDR) as a proxy (substitute) indicator for the

intensity of the emergent light from the two polarisers. It is given that the resistance R of the LDR is

very high when the surrounding is dim and very low when it is illuminated with light.

By varying the angle θ between the two polarising axes of the polarisers and allowing the light that

passes through these two polarisers to shine on the LDR, he believes that the resistance of the LDR

should vary.

He assumes that R is proportional to 1

𝐼 and hence

2

0

1 1cos

R R

where Ro is the resistance of the LDR when the axes of the two polarisers are parallel.

Design an experiment to verify the relationship between resistance R of the LDR and θ.

You may use any of the other equipment usually found in a Physics laboratory.

You should draw a labelled diagram to show the arrangement of your apparatus. In your account you

should pay particular attention to

(a) the identification and control of variables,

(b) the equipment you would use,

(c) the procedure to be followed,

(d) how the relationship between R and θ is determined from your readings,

(e) any precautions that would be taken to improve the accuracy and safety of the experiment.

This type of question is a daunting one and it requires you to plan for an investigation with little instructions given apart from

what is stated above. It is an open-ended question which means that you need to think carefully about your answer before

you start. For this exercise, we are going to scaffold the steps you will need to take in order to fulfil the requirements of the

question. What normally takes 30 min to complete, we are going to extend to 4 periods to level you up to the expectation.


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Steps Time Tasks

A Done Recalling and engaging prior knowledge to the content (i.e. topic) and context of the question. We have accomplished this in Expt 1807 Part A.

B 15 min Unpacking the question by breaking it down into stages and bite-size tasks.

C 20 min Being familiar with the usage of the apparatus needed for the investigation.

D 25 min The real planning question does not require you to carry out your proposed investigation

but here we are going to give you the opportunity to carry out your suggested experimentation in order to make learning more authentic. Data collection is required.

E 20 min Analysis of result. Conclusion. Is the relationship valid?

Step B - Unpack the question by breaking it down into stages and bite-size tasks.

There are various stages in planning an investigation.

Stages Expectations

Stage 1

Define the problem


This requires you to look at the task that has been assigned and to identify the variables that impact on the problem.

the independent variables (the variables that you control)

the dependent variable (the variable that changes as a result of

you changing the independent variable).

Any other variables that might affect your results and which you need to control – generally by keeping them constant.

Stage 2

Data Collection




Once you have identified the variables, you have to decide on a method.

You have to describe this method. You will most certainly need to include a simple labelled diagram to show the apparatus required and the overall set up. The description should also include how you are going to take

the measurements (i.e. specify the instruments to be used) and how you intend to control any variables that might lead to the relation between the independent and dependent variables.

Scientific investigation requires that the results or observation be reliable

(i.e. when repeated measurements are performed under the same conditions, it should lead to the same outcome) as well as being accurate and precise (i.e. with minimum systematic and random errors)

Credits are given for being able to identify any safety precautions or concerns before or during the course of the investigation.

Stage 3

Analysis of results

(d) how the relationship between I and θ is determined from your readings,

If a relation is given, you may been tasked to verify its validity. Usually this means you need to linearise the relation.

State clearly the graph that you need to plot to verify the relation. If the question requires you to find an unknown value then you will need to state clearly how you will get it (e.g. from the gradient)


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Now read the question stem again on page 11 and write below an outline (point form is ok) of the

tasks you would do. You may include diagrams. This preliminary step helps you to organise your

thinking process to make for more thoughtful and deliberate planning.

Step B - Unpack the question by breaking it down into stages and bite-size tasks.

Time given : 15 min

Stages Write your steps here.

Stage 1

Define the problem


Stage 2

Data Collection




Stage 3

Analysis of results

(e) how the relationship between R and θ is determined from your readings,


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Step C - Being familiar with the usage of the apparatus needed for the investigation.

Time given : 20 min

In a typical exam planning question, the apparatus list may or may not be given and so you need to

be familiar with the laboratory equipment and decipher what items you will need to carry out the

investigation. Remember that the relevant instrument used to measure each variable needs to be

specified (e.g. a micrometer screw gauge is used to measure the thickness of the wire).

For Expt 1807 Part B, these are the apparatus provided for you.

2 sheets of polariser (25mm x 25mm) attached to the bottom of the paper/plastic cups

1 large plastic cup

1 thin strip of sticker paper (for student to mark on the plastic cup for reference)

1 small paper cup with a circular protractor scale (in the form of a strip of paper) attached around its rim

1 torch light

2 sets of V-shaped holders to rest the paper and plastic cups on

2 retort stands, bosses and clamps (one to hold torch light, another to hold LDR)

Half metre rule

1 pair of wooden blocks (to sandwich the LDR wire)

An LDR

Multimeter with 2 connecting wires.

Experimental Setup

To be done as pair-work. Discuss with your partner how to go about setting up the investigation.

Draw a schematic diagram of your preliminary experimental setup.

The tutor will come around to check on your ‘design’. Explain your model. No data collection is required now. Only after the experimental setup is approved by your tutor, will you begin your data collection.

Apparatus


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For tutors

There are a few things to look out for. This list is not exhaustive.

1. The lightmeter is not given and so they cannot measure the intensity of light directly. Instead an LDR is provided. After inspecting their models, you will need to explain how the LDR and the ohmmeter can be used as a proxy indicator for light intensity.

2. The polarising axis are not known. They will need to think of ways to identify the relative position of the polarisers’ axis.

3. The LDR needs to be held facing the light source directly. This is done by clamping it with a pair of wooden blocks. The LDR must be kept at the same distance from the polarisers.

4. For more reliable data, we need to minimise the ambient light. So the lab’s lights should be turned off and curtains drawn. Let the students figure this out.

5. When doing a trial run, the ohmmeter reading may fluctuate rapidly. As long as the changes (eg ±10) is small relative to the absolute value (500), it is ok to record the ‘average’ or when the reading is ‘stable’.

6. After you have gone through the rounds, you may summarise the main points for them to consider before setting up the experiment correctly to collect data.


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Step D – Carrying out your suggested experimentation and collect data.

Time given : 25 min (for objective 4)

Draw a schematic diagram of your final experimental set-up. Outline here how you would carry out the experiment. When you have settled on the conditions, you can start with the data collection.


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A table is provided here to help in your data collection.

Angle / o R / cos2 𝑅𝑜

𝑅

0 R0 = …….. 1.00 1.00

10

20

30

40

50

60

70

80

90 0

100

110

120

130

140

150

160

170

180

Plot a suitable graph on page 18 for the range 0 o < < 180o to verify the relation 2

0

1 1cos

R R

State what you would put for the y and x axes.

……………………………………………………………………………………………………………………….….. A graph Ro/R against cos2 is plotted. A straight line passing through the origin is expected.


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19

Actual Results

0.000

0.200

0.400

0.600

0.800

1.000

1.200

0 . 0 0 0 0 . 2 0 0 0 . 4 0 0 0 . 6 0 0 0 . 8 0 0 1 . 0 0 0 1 . 2 0 0

RO/R VS COS2


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Write down your observation on the table here about the graph you have plotted and check if there is

any discrepancies between your prediction and your actual results. Account for the differences if any.

Conclusion Predict Write down what you expect to see.


Explain

What graph is plotted?

Did you get a linear relationship?

A graph Ro/R against cos2 is plotted.

A graph of 𝑅𝑜

𝑅 against cos2 is

plotted.

A linear graph is expected with the straight line passing through the origin.

If yes, what does the graph tells you about Malus’ law?

The straight best fit line passing the origin shows that the relation is valid.

The result is consistent with Malus’ Law as the graph is a straight line passing through the origin.

If no, what factors could have cause the results to deviate?

The ‘best fit’ line does not pass through the origin. So the relation is not satisfied completely.

The trend is not really linear.

It can be attributed to the uncertainty in the measurement of

the angle ,

The fact that the light from a point source spread out according to the inverse square. The light ray is not parallel.

Cannot completely shield the ambient light which interfere with emergent light.

The LRD resistance may not be exactly inversely proportional to the light intensity.

The polariser is not ideal.

0.000

0.500

1.000

1.500

0 . 0 0 0 0 . 5 0 0 1 . 0 0 0 1 . 5 0 0

R O / R V S C OS 2


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Student Questions for Post-Experiment Reflection.

Please scan the QR code to answer a short survey on your experience carrying out this planning exercise for Expt 1807.

Your feedback will help us to bridge your learning needs for future lessons.

1. The steps through the inquiry approach enable me to reflect on my own assumptions. 2. The various steps used here to prepare for planning questions helps me to better

understand the skills required to answer them.

3. Having the teacher as a guide at the side helps me to better understand than the teacher giving mass instruction to the class.

Any Comment.


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For Teachers’ Information Extracted from: STP (Opal) HOME > PEDAGOGICAL PRACTICES > LESSON PREPARATION > PLANNING KEY QUESTIONS

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FEEDBACK > TWO-STEP MULTIPLE CHOICE QUESTION HOME > PEDAGOGICAL PRACTICES > LESSON ENACTMENT > CONCLUDING THE LESSON > MY VISUAL REPRESENTATION

WHAT AND WHEN TO USE STAR is an authentic inquiry approach to learning that piques the students’ interest.

1. Scenario analysis: students are given authentic scenarios or problems designed by teachers. Students

will analyse the given scenario and identify the key learning issues.

2. Team inquiry: students go through repetitions of collaborative inquiry or problem solving with scaffolds

provided by teachers.

3. Application: students apply what they have learned, and propose explanations or solutions to address

the scenario and related learning issues.

4. Reflection: teacher and students evaluate and discuss what has been learned. Students reflect on

their learning and on the learning process.

The first stage of STAR provides the opportunity for teachers to attract students’ attention and pique their

sense of curiosity.

The second stage offers opportunities for teachers to design either open- or guided-inquiry activities for

students to work in teams. It helps the students build 21st century competencies such as problem solving,

communication, and collaborative skills.

The third stage provides students avenues to apply what they have learned to an authentic situation. This

helps them see the connection between the topics they learn and their personal lives.

Lastly, the reflection process allows the students to think about, and deliberate on, what has been learned

and on the learning process. This is important for students as they will learn to self-regulate when they

review their strengths, weaknesses, learning, and study strategies. It can help students to have a greater

sense of ownership of their learning.

This Teaching Action can be considered when situating the learning content in a real-world context so that

students can see the relevance of what they learn and its application. The focus here will be on how it can

be used to start a lesson.



https://opal.moe.edu.sg/stp/pedagogical-practices/lesson-preparation



https://opal.moe.edu.sg/stp/pedagogical-practices/lesson-preparation




https://opal.moe.edu.sg/stp/pedagogical-practices/lesson-enactment/activating-prior-knowledge




https://opal.moe.edu.sg/stp/pedagogical-practices/lesson-enactment/facilitating-collaborative-learning



https://opal.moe.edu.sg/stp/pedagogical-practices/assessment-and-feedback

https://opal.moe.edu.sg/stp/pedagogical-practices/assessment-and-feedback/checking-for-understanding-and-providing-feedback

https://opal.moe.edu.sg/stp/pedagogical-practices/assessment-and-feedback/checking-for-understanding-and-providing-feedback




https://opal.moe.edu.sg/stp/pedagogical-practices/lesson-enactment/concluding-the-lesson


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HOW TO DO IT Step 1:

Describe how this Teaching Action will be carried out, and explain its purpose to your students. Provide

guidelines for the discussions that follows.

Step 2:

Present the scenario or mystery to the class.

Step 3:

Give students a few minutes to think about and to analyse the scenario.

Step 4:

Listen in, prompt, and invite students to share their views and explanation to the whole class.

Step 5:

Build on or clarify their understanding as the lesson progresses.

This Teaching Action can be expanded to include all the stages in STAR to guide student inquiry

throughout the topic. You can do the following:

1. Present the scenario or mystery to the class.

2. Give students a few minutes to think about and to analyse the scenario.

3. Choose to organise your students into groups of three to five with an even distribution of students at

different stages of learning.

4. Coach your students through the scenario, problem or mystery.

5. Skilfully scaffold the learning by asking questions and listening in to their discussions.

6. Invite each group to present its findings, views and explanations to the whole class (alternatively, the

groups can present to another group before they are invited to present to the whole class).

7. Build on their understanding as the lesson progresses.

EXAMPLE Example 1

Below is a scenario for the topic 'Three States of Matter' for a lower secondary science lesson.

In a petrochemical company, a new manager decided to change the work flow drastically. He cut the cost

of doing business by transporting fuels in gaseous state instead of liquid form. His colleagues knew that

this change would be problematic.

What is the relationship among ‘solid’, ‘liquid’ and ‘gas’?

What are the different states of matter?

What are the properties of the different states of matter?

How does the gain or loss of heat affect the properties of solids, liquids, and gases?

How do matters convert between the different states?


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Example 2

Below is a mystery for the topic 'pH Value, Acids, Bases and Salts' in an upper secondary chemistry

lesson.

John and his cousin were both sweet potato farmers. He found that his crop yield was not as much as his

cousin’s, who had a farm next to his. Like his cousin, he watered and weeded the plot of land regularly.

The only difference is that while his cousin limed his plot and took a two-week vacation break before he

added the fertilisers, John was more hardworking: he did not take any break between liming and adding

fertilisers. John thought he would have harvested more sweet potatoes since he had a two-week

headstart.

What problems or issues do you think John was facing?

What happened in the two weeks between the addition of lime and fertiliser?

What could he have done to overcome his problem?

What is lime? What are fertilisers?

What is the importance of adding lime to soil?

POINTS TO NOTE 1. Share with your students the rationale for using this Teaching Action and establish the routine with

them regarding the following:

a. Movement: To minimise movement, the most efficient way of grouping is to have the students

seated in front turn around to face the two behind. Though this minimises movement, it may be

necessary to consider whether the groups have a good mix of students.

b. Attention cues: This is key in group work as you may need to give further instructions or

clarifications, or draw students’ attention back as a class. One effective attention cue is to raise

one hand and let the students know that when they see you doing this, they should do likewise

and stop their activities and discussion, and to focus on you.

c. Norms of discussions: creating a safe environment for group discussion is important so that they

can share their ideas freely in the group. A possible strategy is to use the acronym: THINK (T: Is

it True?, H: Is it Helpful?, I: Is it Inspiring?, N: Is it Necessary?, and K: Is it Kind?). This can be

shared with the class at the start of the school year or when group discussion is introduced for the

first time.

2. The heart of a guided-discovery problem is the guiding questions that your students answer along the

way. While you cannot be present at every group to ask those questions, a carefully planned and well-

designed hand-out can help you to do the job. Questions can be included in the hand-out, and your

students can use it to effectively guide their discussion and discovery. Designing these questions is a

delicate balancing act as you want to provide just enough help so that your students are sufficiently

challenged and thrilled, and are not overwhelmed by the number or difficulty level of the questions.

3. Some possible adaptations of this Teaching Action are as follows:

a. For older or high-achieving learners: you may remind them that the best way to learn something

is to teach it. Clue them in on the scaffolding techniques of facilitating students' work without giving

away the answers.


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b. For younger or low-progress learners: you can help by asking or providing more scaffolding

questions, by providing a piece of information or by explaining a concept. The teacher may also

allow different modes of presentation, for example, drawings to express students’ thoughts.

4. A scenario, problem or mystery can be incorporated into most lessons. It can be carried out as part

of a learning cycle, such as the Biological Sciences Curriculum Study 5E Inquiry (Bybee, Taylor,

Gardner, Van Scotter, Powell, Westbrook & Landes, 2006) or problem-based learning (Finkle & Torp,

1995). At the introduction, the teacher’s role is to motivate and to raise students' interest in the subject.

This can be done through introducing a problem scenario, an activity, a discrepant event or experience

that allows students to connect current learning with past knowledge and experiences. This can be

followed by a series of intriguing questions. This stage is critical because it sets the stage for the

learning that will take place subsequently. Through the series of guided questions, students will

understand the scenario, overcome the problem, and achieve the learning goals. The learning is

enhanced when students are asked to share with the class their approaches to learning and their

solutions.

REFLECTION QUESTIONS 1. What is my key learning from activating my students’ prior knowledge through the use of STAR?

2. What worked well, and why? What would I want to improve the next time around?

3. How can I modify or adapt what I did for students of other profiles, and why?

https://opal.moe.edu.sg/stp/pedagogical-practices/lesson-enactment/arousing-interest/discrepant-events

2018 h2 physics light polarisation and malus’ law · 2019-01-17 · 2018 h2 physics light...

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