Student Exploration: Ray Tracing (Lenses)

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Archibald Cooper
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1 G T: r use te Explre Learning App n te ipad Class Cde: BAHPGNUHVR Name: Date: Student Explratin: Ray Tracing (Lenses) Vcabulary: cncave lens, cnvex lens, cal pint, image, magniicatin, real image, reractin, virtual image Prir Knwledge Questins (D tese BEFORE using te Gizm.) Agnes is trapped n a desert island wit nting but a magniying glass. Se wants t use te glass t cus sunligt and start a ire. Se lds te glass abve sme dry grass as swn at rigt. 1. On te diagram, draw te pat te Sun rays will likely take rm te magniying glass t te grass. 2. A magniying glass is an example a cnvex lens a lens tat curves utward n bt sides. Wy is a cnvex lens useul r starting ires? Gizm Warm-up Te Ray Tracing (Lenses) Gizm sws ligt rays passing trug a lens. Te ligt rays are bent by reractin as tey pass trug te lens and rm a cused image t te rigt te lens. T begin, turn n te Clrize lines ceckbx. Under Sw lines, turn te Central line and te Line trug cal pint s tat nly te Parallel line is swing. 1. Te blue dts in rnt and beind te lens are te cal pints te lens. Mve te candle n te let back and rt and up and dwn. Wat is always true abut te ligt ray tat emerges rm te rigt side te lens? 2. Turn te Parallel line and turn n te Line trug cal pint. Mve te candle. Wat d yu ntice abut tis line?

Activity A: Real and virtual images Get te Gizm ready: Turn n te Parallel line, Central line, and Line trug cal pint. Mve te candle t -24 n te central axis, wit te cal pint at -12.

2 Activity A: Real and virtual images Get te Gizm ready: Turn n te Parallel line, Central line, and Line trug cal pint. Mve te candle t -24 n te central axis, wit te cal pint at -12. Intrductin: A cnvex lens is called a cnverging lens because it cuses ligt rays int a pint. A real image is rmed were te ligt rays emitted rm a pint cnverge n te ter side te lens. I yu placed a seet paper at te image, a cused image wuld be prjected nt te paper. Questin: Hw d lenses create images? 1. Observe: In its current cniguratin, te distance rm te candle t te cal pint is 12 units and te distance rm te cal pint t te lens is als 12 units. A. Wat d yu ntice abut te rientatin te candle s image n te rigt side te lens? B. Wat d yu ntice abut te size te image? 2. Investigate: Cmplete eac actin listed in te table belw, and describe w tat actin aects te image t te rigt te lens. Return te candle and cal pint t teir riginal psitins (-24 r te candle, -12 r te cal pint) ater eac actin. Actin Eect n image Mve te candle t te let. Mve te candle t te rigt. Mve te let cal pint t te let. Mve te let cal pint t te rigt. 3. Analyze: Hw is te image size related t te distance between te candle and te cal pint? _ (Activity A cntinued n next page)

3 Activity A (cntinued rm previus page) 4. Explre: Mve te candle t -12 and te cal pint t -24. Srten te candle t see te wle image. Wat d yu ntice wen te candle is between te cal pint and te lens? Te image yu see is called a virtual image because n actual ligt rays are cused tere. Te dtted lines represent lcatins rm wic ligt appears t be cming t an bserver lcated let te lens. An bserver wuld perceive a magniied virtual image te candle. Tis is wat appens wen yu lk at an bject trug a magniying glass. 5. Investigate: Return te candle t -24 and te let cal pint t -12. Under Sw speciic line segments, turn Apparent ligt lines. On te menu at lwer rigt, select Cncave lens. A cncave lens curves inward n bt sides. A. Wat d yu ntice abut te tree lines ater tey pass trug te cncave lens? Because a cncave lens causes ligt rays t spread apart, it is als called a diverging lens. B. Turn n Apparent ligt lines. Is te image te candle a real image r a virtual image? Explain. (Hint: Recall tat a real image rms were ligt rays are cused.) C. Mve te candle back and rt. N matter were te candle is placed, wat is true abut te image? D. Wat wuld an bserver see i se lked at te candle trug te cncave lens? 6. Summarize: Wat are te dierences between te images rmed by cnvex and cncave lenses?

4 Activity B: Tin-lens equatin Get te Gizm ready: Select te Cnvex lens. Mve te candle t -15 and te cal pint t -10. Turn all line segments, and turn n Sw ruler. Questin: Hw is te psitin te image related t te psitin te bject and te cal lengt te lens? 1. Measure: In tis activity, yu will measure te relatinsips between several values: d : Distance between bject and lens : Distance between cal pints and lens d i : Distance between image and lens Wat are te current values tese variables? (Nte: I yu like, use te ruler t measure d i.) d = = d i = 2. Gater data: Use te ruler t measure d i r eac te llwing values d and. Fr te last tree rws te table, use yur wn values d and. d d i 1 d 1 d i Calculate: Find te reciprcal eac value and ill in te last tree clumns te table Analyze: Fr eac rw te table, ind te sum and. d d i Wat d yu ntice? (Activity B cntinued n next page)

5 Activity B (cntinued rm previus page) Make a rule: Express te relatinsip between,, and as an equatin. d d i = Tis equatin is called te tin lens equatin because it assumes a very tin lens. Errrs are intrduced wen a ticker lens is used. 6. Practice: A candle is placed 6 cm in rnt a cnvex lens. Te image te candle is cused n a seet paper tat is exactly 12 cm beind te lens. Wat is te cal lengt te lens? Sw yur wrk: 7. Practice: A candle is placed in rnt a cnvex lens wit a cal lengt 5 cm. Te image te candle is cused n a seet paper tat is exactly 15 cm beind te lens. Wat is te distance rm te candle t te lens? Sw yur wrk: 8. On yur wn: Use te Gizm t determine i te tin-lens equatin applies t a cncave lens. Reprt te results yur investigatin belw. (Hint: I te image is virtual, d i and are negative.)

Activity C: Magniicatin Get te Gizm ready: Select te Cnvex lens and turn n Sw ruler. Mve te candle t -15 and te cal pint t -10. Adjust te eigt te candle t 5.0 units.

6 Activity C: Magniicatin Get te Gizm ready: Select te Cnvex lens and turn n Sw ruler. Mve te candle t -15 and te cal pint t -10. Adjust te eigt te candle t 5.0 units. Questin: Wat determines te magniicatin an image? 1. Measure: Wat are te current values tese variables? d = = d i = 2. Measure: In additin t te variables yu explred in te previus activity, yu will nw investigate several ters. Measure eac tese variables and list teir values belw. : Object eigt i : Image eigt s : Object-cal pint distance s i : Image-cal pint distance = i = s = s i = 3. Gater data: Use te values abve t ill in te irst rw te table. Ten run yur wn experiments t ill in te last tree rws: d d i i s s i d d i i s s i Calculate: Calculate te given ratis t ill in te last ur clumns te table. 5. Analyze: Wat d yu ntice abut te ur ratis? (Activity C cntinued n next page)

7 Activity C (cntinued rm previus page) 6. Make a rule: Te magniicatin an image is equal t te rati te image eigt t te bject eigt. Using te ratis rm te table n te previus page, write tree equatins tat culd be used t calculate magniicatin: i i = = = i 7. Practice: A candle is placed 4 cm in rnt a cnvex lens. Te image te candle is cused n a seet paper tat is exactly 10 cm beind te lens. Wat is te magniicatin te image? Sw yur wrk: 8. Practice: A 29-cm pencil is placed 35 cm in rnt a cnvex lens and illuminated by a sptligt. Te cal pint te lens is 28 cm rm te lens. A. Wat is te eigt te pencil s image? B. Hw ar rm te lens will te image te pencil be cused? Sw yur wrk: 9. Callenge: Wen te bject is between te cal pint and te lens, s is negative. Wat ter values must be negative r yur equatins t still wrk? Explain. (Hint: Te distance between te cal pint and lens () is never negative unless te lens is cncave.)

Physics 30 Lesson 9 Optics Thin Lenses

Physics 30 Lesson 9 Optics Thin Lenses Reer t Pearsn pages 677 t 68. Physics 30 Lessn 9 Optics Thin Lenses The stuy lenses is very similar t that curve mirrrs. Hwever, while mirrrs invlve relectin, lenses invlve reractin. In act, r lenses there