PAG 05.1 Determining The Wavelength Of Light Using A Diffraction Grating Flashcards
What safety precautions should be taken when operating a laser?
-never look directly at the beam
-ensure no reflective surfaces are in the laser’s vicinity
-display a warning notice so others know that a laser is in use
Why should the screen you use to display the interference patterns on have a matte finish?
A matte screen should be used to reduce the likelihood of the laser beam reflecting from the screen in to someone’s eye and causing harm
What is monochromatic light?
Monochromatic light is a light of a single wavelength (or frequency)
What does it mean if two light sources are coherent?
Coherent sources have the same wavelength and a constant phase difference
What happens to light as it passes through a slit?
Light diffracts as it passes through a slit, with the maximum diffraction occurs when the slit spacing matches the light’s wavelength
Why do bright fringes form on a screen when light is passed through a diffraction grating?
The light diffracts as it passes through the slits and these diffracted waves meet and undergo superposition. At position where the waves meet in phase, constructive interference occurs, and bright fringes are formed
Why do dark fringes form on a screen when light is passed through a diffraction grating?
The light diffracts as it passes through the slits and these diffracted waves meet and undergo superposition. At positions where the waves meet in antiphase, destructive interference occurs, and dark fringes are formed
What equation is used to determine the wavelength of light when using a diffraction grating?
n lambda = d sin(theta)
n: order of diffraction pattern
lambda: wavelength
d: diffraction grating spacing
theta: angle from centre
How is a diffraction grating spacing calculated?
The diffracting grating spacing is the reciprocal of the number of lines per metre
How can the angle from the centre to a higher order line be calculated?
The distance from the diffracting grating to the screen (D) and the distance from he centre of pattern to the higher order line (h) can be measured. The angle is then given by trigonometry
How does a diffraction pattern from a double slit experiment compare to one from a diffraction grating?
As the number of slits increases, the pattern becomes sharper and brightness of the fringes increases. This is because more rays are reinforcing the pattern
Suggest a use for a diffraction grating
Diffraction gratings can be used instead of prisms to analyse spectra. An example use is in X-ray crystallography
Where will the zero order maximum be positioned?
The zero order maximum will be found on the screen, straight ahead of the laser beam, once it has passed through the diffraction grating
Describe the nature of the light emitted by a laser
Lasers produce monochromatic, coherent light that is collimated (consists of parallel rays)
Describe the interference pattern produced if white light is passed through the diffraction grating
A central bright white fringe will be produced. All other bright fringes would consist of a spectra of light, with blue light on the side closest to the centre, and red on the far side of each fringe
