IB Physics SL C 3 9 Young Double Slit Equation Questions

Practise IB Physics SL C.3.9 by using the Young double-slit equation to calculate fringe spacing, wavelength, screen distance and angular separation.

Exam points

Rearrange s = λD/d to calculate fringe spacing, wavelength, slit separation or screen distance.
Check units and powers of ten when solving double-slit fringe-spacing problems.
Use fringe geometry or angular separation to connect measured patterns with wavelength and slit spacing.

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Study C.3.9—Young double-slit equation conceptsOpen the corresponding Concept lesson for explanations, examples and exam connections.

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This question is about interference.

Light from a laser is incident on two identical parallel slits. The light from the two slits produces a fringe pattern on a screen.

Figure for Question IB Physics SL C 3 9 Young Double Slit Equation Questions question 1 — IB Physics SL

A central bright fringe is produced at C . The next bright fringe is produced at A . There is a dark fringe at B .

The distance from the two slits to the screen is 1.5 m . The distance BC is 1.8 mm and the distance between the slits is 0.30 mm .

Show that the laser produces light of wavelength equal to 720 nm .

use of $\lambda=\frac{s d}{D}$ ;
$s=\underline{2} \times 1.8(\mathrm{~mm})$ ;
(award this mark for any evidence for the factor of 2 )
$\lambda=\frac{2 \times 1.8 \times 10^{-3} \times 0.30 \times 10^{-3}}{1.5} /$ OWTTE;
( $=7.2 \times 10^{-7} \mathrm{~m}$ )

Exact answer is given, award marks for correct working.

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IB Physics SL C 3 9 Young Double Slit Equation Questions question 1