IB Physics Exam Preparation - Waves - Double slit and diffraction gratings

This video is aimed at IB students studying HL or SL Physics. It can also help students preparing other diplomas in getting grips with the subject.

In this episode, we will be working on an exercise inspired by a past paper that deals with double slit interference patterns and diffraction gratings (Waves).

An exercise will appear on the screen. Pause the video and work it out by yourself. Then, we will review the exercise together. Questions a to d are suitable for SL students. HL students, please work on all questions.

This video is produced and presented by Edouard Reny, Ph.D. in materials sciences and private tutor in Physics. http://www.physics-tutor.nl/

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******* Exercise Text *********** A light of unknown wavelength illuminates two slits that are distant of 0.210 mm from each other. The widths of the slits are negligible.

On a screen located at a distance of 3.20m from the pair of slits, bright fringes are observed. The maxima of the fringes are separated by 1.00 cm.

a/ Explain how the fringes form. (2 Marks)

b/ Determine the wavelength of the light that passes through the slits. (3 Marks)

c/ The intensity of the light on the screen due to one slit is 15 W/m^2. Plot on a graph how the intensity of the light passing through the two slits varies on the screen with the distance from the middle of the central fringe. (3 Marks)

d/ The two slits are now replaced with two slits of non-negligible width. Sketch another graph of the interference pattern that would be observed on the screen. (2 marks)

e/ The two slits are removed and replaced by a diffraction grating. The second order maximum of the light appears for an angle of 62 degrees. How many slits does this grating have in one millimeter? (2 Marks)

f/ Another beam of visible light illuminates the grating. It creates a maximum at the same angle as in e/. The order of that maximum is different. Determine the wavelength of this beam and the order of this maximum. (2 Marks) ... https://www.youtube.com/watch?v=ElQ_5chh6YE