18012022 Interference Diffraction Grating Summary Notes pages 23

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18/01/2022 Interference & Diffraction Grating (Summary Notes pages 23 -24) Particles and Waves M

18/01/2022 Interference & Diffraction Grating (Summary Notes pages 23 -24) Particles and Waves M Ashton 2013

What are we learning today? �The effect of a grating on a monochromatic light

What are we learning today? �The effect of a grating on a monochromatic light beam. �Calculations using the equation dsinq = nλ. �measure the wavelength of a monochromatic light source.

What is a Grating? �It is a slide that consists of many equally spaced

What is a Grating? �It is a slide that consists of many equally spaced slits positioned extremely close together. �Light is diffracted as it passes through each slit. �This causes interference to take place.

Demonstration (VPL simulation) �Your teacher will demonstrate the effect of a diffraction grating on

Demonstration (VPL simulation) �Your teacher will demonstrate the effect of a diffraction grating on laser light. �Watch carefully and note what happens to the pattern as �the number of slits per mm increases. �the distance to the screen increases. �the wavelength of the light increases.

�Increasing the number of slits per mm increases the distance between maxima. �Increasing the

�Increasing the number of slits per mm increases the distance between maxima. �Increasing the distance to the screen increases the distance between maxima. �Increasing the wavelength increases the distance between maxima.

The Grating Equation �For a grating ml = d sinq m = order of

The Grating Equation �For a grating ml = d sinq m = order of maximum λ = wavelength of light d = distance between slits on diffraction grating θ = angle between central maximum and maximum of order m

NB The slit separation, d, is very often given as slits, or lines, per

NB The slit separation, d, is very often given as slits, or lines, per millimetre. Example: What is the slit separation for diffraction grating with 300 lines per mm? 300 x 1 000 = 300 000 slits per m

Example ml = d sinq �Calculate the wavelength of light passing through a diffraction

Example ml = d sinq �Calculate the wavelength of light passing through a diffraction grating, when the first order maximum is produced at an angle of 21°. The grating has 600 lines per mm.

Example mλ = d sinθ �Light of wavelength 700 nm is shone through a

Example mλ = d sinθ �Light of wavelength 700 nm is shone through a diffraction grating that has 120 slits per millimetre. Calculate the angle between the central and second order maximum.

Activity ID L 3: Measuring the wavelength of laser light Do not point the

Activity ID L 3: Measuring the wavelength of laser light Do not point the laser at anyone or look directly at the beam. Expected value of λ is: 651± 2 nm.

mλ = d sinθ Structured Problems, page 32, Qs 79 -85.

mλ = d sinθ Structured Problems, page 32, Qs 79 -85.

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