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Marr College Physics

Higher Physics

Researching Physics Unit

Candidate Guide

Page

1. Introduction 1

2. Selecting your topic and experiment 2

3. Maintaining a record of research – the “daybook” 3

4. Links to underlying physics 7

5. List of experiments and instructions 10

Optoelectronics – the science and technology at the heart of 21st Century

telecommunications – LEDs and Optical Fibres

1

Introduction

This unit focuses on the skills involved in carrying out a research project. You will undertake

literature based background research to learn and report on the underlying physics of your project

topic. You will then carry out a practical investigation involving two related experiments.

Your research, underlying physics and your findings will be documented in a “record of research”

also known as a “daybook”.

Your daybook will be marked by your teacher against the success criteria on page 4 in this guide.

You will then use your daybook to produce an Assignment Report to be submitted to SQA for

external marking – and this contributes 20 % of your external grade.

What about teamwork?

As in the world of work, it is likely that you will undertake the research project as part of a group.

Sometimes, within your team, you will be undertaking the same task and other times you will each

focus on a different part of the task. In either case, it is important that discussion takes place and

specific tasks are allocated so that each individual does not waste time answering the same

question.

Agree the part that each member of the team will play and ensure that there is time to share the

results of the work.

Record the specific contribution of each team member in your daybook.

2

Selecting your topic and experiments

Optoelectronics: The Science and Technology at the Heart of 21st Century

Telecommunications

The context for your work is the application of optoelectronics devices in modern

telecommunications. Telecommunications has been revolutionised in recent years due to

developments in optoelectronics devices. The development and use of light emitting diodes (LED),

laser diodes, photodiodes and optical fibres and liquid crystal displays (LCD) has led to the internet,

mobile telephones and a whole range of handheld interactive devices and large flat screen displays.

Your project can focus on either:

1. LEDs

2. Optical Fibres

With your team members, look at the web links to underlying physics, and the suggested

experiments, and decide which application you want to focus on.

You can then select two of the suggested experiments to undertake, and study the underlying

physics involved.

3

Maintaining a record of research

Physicists and scientists all maintain a record of research – this continual journaling and

recording enables to project to be driven forward and allows others to follow the thought

processes and evolution of the project, including changes and modifications as the project

develops.

Physicists then use their records to generate reports which more coherently explain their aims

and findings.

You will follow this process by maintaining a “daybook” (record of research), which will be

internally marked as a Unit by your teacher.

You will then use your daybook to produce an Assignment Report which will be sent to SQA for

external marking and contributes 20 % of your grade for Higher.

Your daybook must contain:

1. A dated log of your research activities, which is continually updated as you progress

through the project.

2. Underlying Physics

A clear statement describing the underlying physics involved in your research topic

Reference to at least two relevant sources of information / data

o Enough detail should be given to allow a third party to retrieve the sources

3. Practical research – an investigation involving two separate but related experiments

(a) Planning the practical investigation

A clear aim for the practical research investigation

A clear and detailed description of how the practical research investigation should be carried

out, including safety considerations

Measurements to be made

(b) Carrying out the practical investigation

Your teacher must observe you carrying out the experiments safely

Data must be recorded correctly using appropriate tables with headings and units

For 3 (a) and (b) – planning and carrying out the investigation, it is strongly recommended that, for

each experiment, you follow the format of an Outcome 1 experiment report (see pages 5 and 6).

Either experiment is suitable for the production of an Outcome 1 report - your teacher may request

that you use one of your experiments to submit an internal experiment report. This is a requirement

of Higher Physics unit assessment.

Your teacher will mark your daybook based on the above, using the Marking Instructions shown on

the next page.

4

Marr College Physics

Higher Physics –Internal Unit Assessment – Researching Physics Unit

Student Name - Assessor:___________________________

Assessment Standard

Making Assessment Judgements Additional Guidance Achieved? Assessor Comments

1.1 Gathering and recording information from two sources relating to the chosen topic.

The recorded information should include:

a clear statement describing their research topic

reference to at least two relevant sources of information/ data

enough detail should be given to allow a third party to retrieve the sources

Evidence must demonstrate that the candidate has a clear understanding of the physics related to the topic.

The candidate should use terms and ideas that are correct and at a depth appropriate to Higher Physics.

A formal referencing system may be used but candidates will not be penalised if this is not complete and sources can be retrieved by a third party using information supplied.

2.1 Planning /designing the practical investigation, including safety measures.

The plan should include:

a clear aim for the practical research

investigation

a clear and detailed description of how the

practical research investigation should be

carried out, including safety

considerations

observations/measurements to be made

The plan for the practical research investigation must be clear enough for another person to follow and at an appropriate level.

The plan may include labelled diagrams.

Candidates must keep a record of their progress.

2.2 Carrying out the practical investigation safely, recording detailed observations/

measurements correctly

The candidate should be observed to

follow procedures safely

observations/measurements should be recorded correctly and results presented in an appropriate format. Where appropriate these should be repeated.

An observation checklist for the experimental stage supported by assessor comment, as appropriate, could be used as evidence.

Raw data must be recorded.

Candidates should present findings in an appropriate format ie table, line graph, or summary. Labels and units must be correct.

Candidates must keep a record of their work.

RESULT

PASS

RESUBMIT

5

The following guide is used for Higher Outcome 1 – a scientific report of a practical investigation –

and is ideal for the planning and carrying out of your experiments

Marr College Physics

Higher Physics

Outcome 1 – a scientific report of a practical investigation

All report writing should be done in the third person and follow the structure outlined below.

Title

Give the investigation an appropriate title.

Aim

State clearly what you are investigating in terms of the dependent and independent variable, e.g. to investigate the relationship between the angle of a slope and the acceleration of a trolley.

Independent / Dependent variables

State clearly what the independent and dependent variables are in your investigation.

The independent variable is the one that you are in charge of and altered during the investigation.

e.g. in an investigation into the effect that the angle of a slope has on the acceleration of a trolley:

o The angle of the slope is the independent variable. o The acceleration of the trolley is the dependent variable.

Variables to be kept constant

List the other variables in your investigation that you will keep constant to ensure a fair test.

Apparatus

Draw a labelled diagram of the apparatus used.

A good labelled diagram will allow another student to set up the apparatus in the exact same way.

Method

Explain clearly, in short sentences or bullet points, how to carry out the procedure and obtain the data.

A good method is one that another student can read, follow and obtain the same data as you.

Ensure that you explain how you changed the independent variable.

Safety

Explain briefly how you will ensure that the investigation is carried out safely.

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Results

Present your results in a table

Make sure the headings are written in words and you have included the correct units.

All raw data taken should be included.

Your table should have a column for the mean of repeated measurements and a column for the random uncertainty in the mean.

Process the table data - Draw a graph of the results

Write the labels using full words and include the appropriate units.

Uncertainties

Reading uncertainties

For every instrument you used to take measurements, state the reading uncertainty:

e.g. o The reading uncertainty in the angle measurement was ± 0.5° o The reading uncertainty in the acceleration measurement was ± 0.01 ms-2

Random Uncertainties

For repeated measurements, show an example of how you calculated the random uncertainty

e.g. o the random uncertainty in time was calculated as shown:

o

Conclusion

State the connection between the independent and dependent variable.

Make sure that your conclusion answers the aim and is supported by the results

Where possible state if there is direct or indirect/inverse proportion and the evidence for this.

e.g. “I can conclude that current is directly proportional to voltage since the graph above is a best-fit straight line passing through the origin”.

If the line is a best-fit straight line but not through the origin, call the relationship “proportional”.

Evaluation

Suggest at least two possible improvements to your investigation, based on evidence.

Some Examples of Evaluation Statements o A more accurate measure of time would improve the investigation as

the percentage error in time was much larger than the percentage error in distance. o It would have been better to place the thermometer in the flask as this would have

allowed a more direct and accurate measurement of gas temperature.

7

Suitable links to underlying physics - LEDs

The suitability of the links will depend on the experiments that you select. However, for all LED

projects, you should study Band theory of solids and how LEDs work

Band theory of solids

http://www.bbc.co.uk/education/guides/zppnn39/revision

http://hyperphysics.phy-astr.gsu.edu/hbase/solids/band.html

How LEDs work

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/led.html#c2

http://www.cnet.com/uk/news/appliance-science-how-led-lights-work/

http://electronics.howstuffworks.com/led2.htm

http://www.physics-astronomy.com/2014/06/watch-led-light-change-color-in-liquid.html

http://www.educationscotland.gov.uk/Images/SemiconductorsAndBandTheoryH_tcm4-658243.doc

- page 18 recommended

http://www.edisontechcenter.org/LED.html

Switch-on voltage and wavelength/frequency

http://www.exo.net/~pauld/summer_institute/summer_day4+5light/light_energy_vs_color.html -

recommended - shows QV=hf so you can do sample calculations for switch on voltage using

frequency or wavelength

http://www.electronics-tutorials.ws/diode/diode_8.html -recommended - physics and data

LED voltage vs current (hence brightness) graphs

http://www.societyofrobots.com/electronics_led_tutorial.shtml

http://www.electronics-tutorials.ws/diode/diode_8.html - again!

http://www.gizmology.net/LEDs.htm - see Section “Using LEDs”

http://www.pveducation.org/pvcdrom/pn-junction/diode-equation - equations way beyond Higher

level – you can include if you are confident you can explain and demonstrate understanding

Current versus brightness – direct proportion expected

http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/leds.html#c3

http://www.societyofrobots.com/electronics_led_tutorial.shtml

8

Irradiance vs distance

http://www.cyberphysics.co.uk/general_pages/inverse_square/inverse_square.htm

http://www.bbc.co.uk/education/guides/zwwjjxs/revision

http://www.vernier.com/innovate/inverse-square-law-light-experiment-improved/

http://www.pmodwrc.ch/newrad2005/pdfabstracts/Newrad044.pdf - shows that design of LEDs

means that they may not follow standard inverse square law

9

Suitable links to underlying physics – Optical Fibres

Total internal reflection and critical angle

http://www.bbc.co.uk/education/guides/z88dd2p/revision/3

Light transmission with optical fibres

http://www.explainthatstuff.com/fiberoptics.html

http://computer.howstuffworks.com/fiber-optic6.htm

Attenuation/signal loss

http://www.juniper.net/documentation/en_US/release-

independent/junos/topics/concept/fiber-optic-cable-signal-loss-attenuation-dispersion-

understanding.html

Macrobending and microbending

http://www.siemon.com/uk/white_papers/08-03-03-light-it-up.asp

http://www.fibrefab.com/wp-content/uploads/downloads/2012/03/Application-Note-

Microbending-Macrobending.pdf

10

List of experiments and instructions - LEDs

Experiment 1:

Investigating the relationship between LED wavelength and “switch-on” voltage

The LED Investigation Board has a built in supply voltage control which controls the voltage

connected to the LED from the battery.

Connect the battery to the LED Investigation Board.

Select an LED to investigate using the switches.

Connect a voltmeter to the voltmeter connector.

Turn the supply voltage control fully anticlockwise so that the voltmeter reads zero volts.

Gradually increase the supply voltage to the LED using the supply voltage control. Look for the

LEDs lighting.

Record the voltage when the LED starts to produce light.

Repeat for different colours of LED

The wavelengths of each LED have been measured with a spectrometer and are provided:

Colour wavelength(nm)

Red 635

Orange 607

Yellow 595

Green 527

Blue 469

Violet 417

11

Experiment 2:

Investigating the relationship between the supply voltage and the brightness of an LED

The light sensor board can be used to measure the brightness of the red LED as the supply voltage is

altered.

The light sensor board uses a photodiode that generates an output voltage that is directly

proportional to the brightness of the LED.

The light from the LED is directed to the photodiode using an optical fibre.

The gain switch on the Light Sensor Board must be set to the x1 position.

(Photo of setup shown on next page)

voltmeter connector

photodiode

V

photodiode

amplifier

gainx10

x1

LED

light sensor

optical fibre

V

photodiode

amplifier

gainx10

x1

LED

light sensorselect current

R

G

B

vary voltage

LED investigations board

20002mA

4mA

6mA

8mA

10mA

6V

1000

670

500

400

V

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Set up apparatus as shown

Record the supply voltage and the photodiode output voltage using the voltmeters

Use the supply voltage control to increase the supply voltage to the red LED

Repeat measurements over a suitable range of supply voltages

13

Experiment 3:

Investigating the relationship between current and brightness of LED

The left hand panel of the LED Investigations Board allows the current in an LED to be changed.

Use the optical fibre and Light Sensor Board to measure the brightness of the orange LED as the output voltage of the photodiode.

The gain switch on the Light Sensor Board must be set to the x1 position.

Set up apparatus as shown

Record the current from the reading on the board, and the photodiode output voltage using

the voltmeter

Now unplug the orange LED from the 2 mA socket and plug it in turn into the 4 mA, 6 mA,

8 mA and 10 mA sockets and record the photodiode output voltage each time.

select current

R

G

B

vary voltage

LED investigations board

20002mA

4mA

6mA

8mA

10mA

6V

1000

670

500

400

V

orange LED

optical fibre

V

photodiode

amplifier

gainx10

x1

LED

light sensorselect current

R

G

B

vary voltage

LED investigations board

20002mA

4mA

6mA

8mA

10mA

6V

1000

670

500

400

V

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Experiment 4:

Investigating the relationship between irradiance and distance from an LED light source

Connect the Remote LED to the voltmeter connector on the LED Investigations Board.

Place the Remote LED at the zero position on the ruler on Distance Board.

Set the supply voltage control to around its middle setting.

Connect the Remote Photodiode to the Light Sensor Board using its jack plug.

Connect a voltmeter to the voltmeter connector on the Light Sensor Board. It displays the brightness of the light on the Remote photodiode in “light units”. Make sure the gain switch on the Light Sensor Board is in the x1 position.

Clip the Remote LED on to mounting board. Clip the Remote photodiode on to another mounting board.

Place the Remote LED and Remote photodiode on a metre stick so that the distance between them can be measured.

select current

R

G

B

vary voltage

LED investigations board

20002mA

4mA

6mA

8mA

10mA

6V

1000

670

500

400

V

supply voltage control

voltmeter connector

Remote LED

voltmeter connector

Remote photodiode

jack plug

V

photodiode

amplifier

gainx10

x1

LED

light sensor

15

Set up apparatus as shown

Record the distance from the LED using the metre stick, and record the photodiode output

voltage using the voltmeter

Vary the distance between the LED and the detector by moving the detector

Repeat the measurements over a suitable range of distances

16

List of experiments and instructions – optical fibres

Experiment 1:

Investigating how the number of loops in an optical fibre affects the light output

Switch on the battery packs and connect one each to the LED Investigation Board and Light Sensor Board.

Switch on the red LED and turn up its power supply so it is brightly lit.

Connect a voltmeter to the Light Sensor Board to measure the brightness of the light transmitted through the optical fibre. Make sure the gain switch on the Light Sensor Board is in the x1 position.

Connect the optical fibre between the red LED on the LED Investigation Board and the photodiode on the Light Sensor Board.

Set up apparatus as shown

Bend the optical fibre into a small “figure of eight” using the Optical Fibre Bending Board and measure the light transmitted by recording the photodiode output voltage using the voltmeter

Bend the optical fibre round more and measure the photodiode output voltage

Repeat over a suitable number of bends of optical fibre

select current

R

G

B

vary voltage

LED investigations board

20002mA

4mA

6mA

8mA

10mA

6V

1000

670

500

400

V V

photodiode

amplifier

gainx10

x1

LED

light sensor

Optical Fibre Bending Board

to voltmeter

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Experiment 2:

Investigating the relationship between the radius of the loop and the light output from an optical

fibre

Switch on the battery packs and connect one each to the LED Investigation Board and Light Sensor Board.

Switch on the red LED and turn up its power supply so it is brightly lit.

Connect a voltmeter to the Light Sensor Board to measure the brightness of the light transmitted through the optical fibre. Make sure the gain switch on the Light Sensor Board is in the x1 position.

Connect the optical fibre between the red LED on the LED Investigation Board and the photodiode on the Light Sensor Board.

Set up apparatus as shown

Bend the optical fibre around the largest radius using the Optical Fibre Bending Board and measure the light transmitted through it by measuring the output voltage using the voltmeter.

Bend the optical fibre around a smaller radius and record the output voltage of the photodiode

Repeat over a suitable number of radii

select current

R

G

B

vary voltage

LED investigations board

20002mA

4mA

6mA

8mA

10mA

6V

1000

670

500

400

VV

photodiode

amplifier

gainx10

x1

LED

light sensor

to voltmeter