THIN LENS EQUATION ( SNC2D)CONCEPT PRESENTATION

Presented by: Artimis Soltanidji

Instructors: M. Zatzman and J. Extavour HS-Science OISE/UT 2010

Table of Content

Where?, When?, Why? Curriculum Expectations Possible road blocks and strategies Lesson ideas (highlighting A&E

possibilities) Safety considerations Accomodations References

Get ready for the lens song:

http://www.youtube.com/watch?v=6y6O-TTLE4g

Where?, When?, Why?

Where?

The thin lens equation is placed strategically at the end of the optics unit; just before

learning about the eye and optical technologies.

When?

By the time you are ready to teach this concept the students are well versed in the behavior

of light through concave and convex lenses and there various components using ray

diagrams.

Why?

Ray diagrams do not give any information about image distance or the size of the image. The

thin lens equation specifically relates the focal length of a spherical thin lens to the object

position and the image position, therefore, allowing the students to predict behaviours of

light.

This knowledge will allow the students to understand its true relevance in society (i.e. self-

adjusting glasses) and its importance in physics (i.e. optical technologies).

 

Curriculum Expectations

Physics: Light and Geometric Optics Curriculum expectations

Overall ExpectationsE1 Evaluate the effectiveness of technological devices and procedures designed to make

use of light, and assess their social benefits;

E2 Investigate, through inquiry, the properties of light, and predict its behaviour, particularly with respect to reflection in plane and curved mirrors and refraction in converging lenses;

E3 Demonstrate an understanding of various characteristics and properties of light, particularly with respect to reflection in mirrors and reflection and refraction in lenses.

Specific ExpectationsE2.5

Predict, using ray diagrams and algebraic equations, the position and characteristics of an image produced by a converging lens, and test their predictions through inquiry [PR, AI, C]

E3.5

Describe the characteristics and positions of images formed by converging lenses (e.g., orientation, size, type), with the aid of ray diagrams.

Strand A. Scientific Investigation Skills and Career Exploration Curriculum ExpectationA1.5 conduct inquiries, controlling some variables, adapting or extending procedures as required, and using standard equipment and materials safely, accurately, and effectively, to collect observations and data. A1.8 analyse and interpret qualitative and/or quantitative data to determine whether the evidence supports or refutes the initial prediction or hypothesis, identifying possible sources of error, bias, or uncertainty. A1.12 use appropriate numeric, symbolic, and graphic modes of representation, and appropriate units of measurement (e.g., SI and imperial units). A1.13 express the results of any calculations involving data accurately and precisely.

Assumptions/Lack of Prior Knowledge That May Lead to Road Blocks

Assumptions/Lack of Prior Knowledge That May Lead to Road Blocks

#1 Road BlockWeak grasp of behavior of light through lenses and their various components using ray diagrams.

Do not move forward until the students have mastered this concept. You may use ray boxes and gizmo’s to effectively address the learning this skill.

Assumptions/Prior Knowledge That May Lead to Road Blocks

#2 Road BlockStudents may become confused in which type of lens (i.e. concave and convex) to use when dealing with the thin lens equation. This confusion may lead to uncertainty in the sign conventions for the image formed.

Be explicit that the ministry documents only require application of the thin lens equation to convex lenses. Perhaps use a table to show the meaning of the sign convention.Lens

TypeFocal Length

Distance to Object

Distance to Image

Convex Positive Positive Positive or negative depending on object location

Assumptions/Prior Knowledge That May Lead to Road Blocks

#3 Road Block Weak prior knowledge from grade 9 mathematics in substituting and rearranging formulas to solve for a variable.

Substituting and rearranging formulas to solve for a variable is covered extensively in the grade 9 mathematics curriculum. However, if students are struggling with this skill it would be worthwhile to spend some time revisiting this concept.

Remind Students of the TWO simple rules when solving for a variable:

1) Do opposite operations ( +/- & ×/÷)

2) What you do to one side you must do to the other side of the equal sign

Try some sample questions:a) d = rt solve for r b) P = 2l + 2w slove for wc) A = pr2 slove for r

Assumptions/Prior Knowledge That May Lead to Road Blocks

#4 Road Block

Students have not completed the similar triangle unit ingrade 10 mathematics OR they have a weak understanding ofthis concept.

This is a great opportunity for a moment with the math department. Depending on your strengths, you may want to take this opportunity to teach the students about similar triangles from a science perspective OR prior to teaching this concept consult the math department to ensure that the similar triangle unit has been taught.

cross-curricular

Suggested Lesson Sequence

Lesson 1

Briefly introduce the thin lens equation, its components and its relevance to what they have learned so far.

derive the thin lens equation using similar triangle activity. http://hirophysics.com/Anime/thinlenseq.html

solve sample problems emphasizing correct procedure for substituting and rearranging variables.

assign problem set homework.

Assessment Opportunity: Assess accuracy of calculations with think/pair/share

groups Use 3-2-1 as their exit card.

Learning Styles Addressed:

LinguisticVisualInterpersonalLogical

Lesson 2

Address questions regarding homework. Discover the significance of the thin lens equation by performing two inquiry

based activities:Note: please see appendices 2 to 4 for additional inquiry based

activities.

i) BLM-1: This inquiry based activity asks students to suggest an alternative method to determine the focal length of convex lenses.

ii) BLM-2: This inquiry based activity asks students to draw a sequence of careful ray diagrams and to make measurements from the diagrams.

  Revisit the magnification equation and its connection to the thin lens equation. Assign practice problems

Assessment/ Evaluation Opportunities: Assess activity BLM1 by having students share their results with a partner. Collect activity BLM2. Exit cards: “name one important concept you learned today” Remind them of a quiz for the next day

Learning Styles Addressed:

KinestheticVisualInterpersonalLinguisticLogical

Let’s do some work

There are 3 stations set up around the room. Please visit each station Take time to read and answer the required

questions Think about the following questions as you are

visiting each station: I like or don’t like this question because? How can the question be modified to suit

different levels? I can use the question as an assessment “for” by?

Lesson 3

Discuss any outstanding issues with respect to the thin lens equation. 

Discuss real-life relevance (i.e. self-adjusting glasses) http://www.revver.com/video/428203/adaptive-eyewear-solving-an-invisible-problem/

Assessment/Evaluation Opportunities: Class discussion regarding relevance of lenses Evaluation in the form of quiz

Learning Styles Addressed:

InterpersonalLinguisticVisual

Safety Considerations

No real safety consideration is required for this concept unless you are using:

Candles for demonstrations or activities;

Using incandescent light sources. These lights can become very hot and also it is not recommended for students to shine the light into anyone’s eyes.

Accommodations for ESL/ELL/Special Education students

Make flash cards for the terms in bold in the student book; write the term on one side and the definition on the other;

  Look through the section for unfamiliar words or expressions; record these in their notebooks

along with an explanation;  Extensive use of visual cues;  Use of graphic organizers;  Strategic use of students’ first languages;  Allowance of extra time;  Pre-teaching of key words;  Simplification/repetition of instructions as needed;  Simultaneous use of oral and written instructions;  Alternative methods for the student to demonstrate his or her achievement of expectations

(e.g., allowing the student to take tests orally) or the allowance of extra time to complete the assessment.

Annotated References

1. Sandner Sandner et al., Pearson Investigating Science 10. 2009 Pearson Canada Inc. Toronto 

2. Website: Gizmos http://www.explorelearning.com/

 

References 3 and 4 are handy internet mathematical tool can help to determine the distance an object is from the lens, the distance

of the object from the lens, and the focal length of the lens. 

3. Website: An explanation of the formula, as well as a built-in calculator for problems. http://hyperphysics.phyastr.gsu.edu/hbase/geoopt/lenseq.html

4. Website: An amazing interactive thin lens example. http://micro.magnet.fsu.edu/primer/java/components/characteristicrays/index.html

 

References 5, 6, and 7 are internet tool to help check your work and learn more about the thin lens equation.

5. Website: This thin lens simulator allows for both types of lenses and a changing object size and position, and is a great way to check your ray diagrams. http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=48

6. Website: An explanation and references for this problem. http://hypertextbook.com/facts/2008/MonaZawam.shtml

7. Website: More practice with the thin lens equation. http://homepage.mac.com/cbakken/obookshelf/cvreal3.html

8. Five easy lessons “strategies for successful physics teaching” by Randall D. Knight | © 2004 | Addison Wesley | ISBN: 0-8053-8702-1 |