AHL Topic 9 Lesson 4 Single Slit Diffraction

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IB SL Topic 4.4 Wave behaviour & AHL Topic 9.2 Single-slit diffraction Lesson on Single-slit diffraction

Understandings:

SL students: Diffraction through a single-slit and around objects

HL Students: The nature of single-slit diffraction

Applications and skills: SL Students:

Qualitatively describing the diffraction pattern formed when plane waves are incident normally on a single-slit

HL Students:

Describing the effect of slit width on the diffraction pattern

Determining the position of first interference minimum

Qualitatively describing single-slit diffraction patterns produced from white light and from a range of monochromatic light frequencies

Starter: Click on this LINK and complete this Matching Exercise on Wave Properties (3 mins)

Main Activities:

Task #1: Explore and Read (20 mins)

a) Go to the PhET Wave Interference Simulation and/or http://www.acoustics.salford.ac.uk/feschools/waves/diffract3.php and use the simulations to find answers to these questions:

QUESTIONS FOR SL & HL STUDENTS: (20 mins)

1. What happens when wave fronts pass through a single slit or round a barrier?

2. Describe the interference pattern produced (on a distant screen) after light waves incident on a single slit have passed through the opening and travelled different distances to the screen.

ADDITIONAL QUESTIONS FOR HL STUDENTS ONLY:(10 mins)

3. What is the effect on the interference pattern of either reducing the slit width or increasing the wavelength of the waves ie. of decreasing the slit width to wavelength ratio? 4. How does the path difference for two waves differ to produce: a) maxima (bright fringes) b) minima (dark fringes) 5. How does the single-slit diffraction pattern for white light compare with that produced by monochromatic red light and monochromatic blue light?

b) By looking through this Powerpoint on Diffraction, go back and correct or add extra detail to your responses to the questions. (5 mins) Task # 2: SL EXTENSION:

a) Explain how changing the frequency of the light incident on a single-slit alters the diffraction pattern formed. Use labelled diagrams in your answer.

b) Predict the nature of the diffraction pattern made by an opaque disc. (The answer can be found on p850 of the Cutnell & Johnson text.)

HL EXTENSION: Analyse Data: A Look at Relationships Quantitatively

a) Show how to derive the expression - tan theta = y / L

b) Download and complete this Data Analysis Sheet on Interference of Sound. (25 mins)

Task #3: Complete the Questions on Diffraction for your appropriate course level (SL or HL). (15 mins)

Plenary: SL Single Slit Diffraction Plenary: HL Single Slit Diffraction