Diffraction

What is difraction?

The spreading out of waves when they pass through or around a gap.

When does the greatest diffraction happen?

When the gap is the same size as the wavelength, when the gap is smaller than the wavelength most waves are reflected.

What is monochromatic light?

Light that consists of a single frequency, wavelength or colour.

What does the diffraction pattern look like for a laser directed through a single slit?

A central maximum that is much brighter and wider than the other maxima. Bright fringes are areas of maximum intensity and produced by constructive inteference. Dark fringes are areas of minimum intensity and are produced by destructive inteference. On either side of the central maximum, maxima are narrower and get dimmer as the order increases.

In single slit diffraction, how does the slit width affect the diffraction pattern?

The slit width is inversely proportional to the width of the central maximum.

The slit width is inversely proportional to the fringe spacing.

The slit width is directly proportional to the intensity of the central maximum.

In single slit diffraction, how does wavelength affect the diffraction pattern?

Wavelength is proportional to the width of the central maxima.

In single slit diffraction, what does the diffraction pattern of white light look like?

The central maximum is bright white since constructive inteference from all colours happens there. All the other maxima are composed of a spectrum , the shortest wavelength (violet/blue) would appear nearest to the central maximum since it is diffracted less. The longest wavelength (red) appears furthest from the central maximum since it is diffracted more. As the maxima move further from the central maximum the wavelengths of blue observed decrease and the wavelengths of red observed increase. The colours look blurry and further away from the central maximum the fringe spacing gets so small that the spectra eventually merge with no space between them.

What is the diffraction grating equation?

dsinθ = nλ

d= slit seperation

n= order of diffraction pattern

What is the equation for d, regarding N?

d=1/N

d= slit seperation

N= number of lines per millimetre.

How can you calculate the highest order of maxima visible?

The maximum angle of diffraction with which the maxima can be seen is when the beam is at a right angle to the diffraction grating. This means θ =90 and sinθ=1, therefore:

n=d/λ

n= order of diffraction pattern

d= slit seperation

(if you get a n value that is a decimal, you must round down)

What are some uses of diffraction gratings?

Spectrometers, x-ray crystallography and monochromators.

What increases diffraction?

Increased wavelength, making the gap closer to the wavelength.

How do the properties of a wave change after they've been diffracted?

The amplitude changes, the wavelength stays the same.

What happens to a wave after passing through a gap?

They spread out so they have curvature, their amplitude is less because the barrier on either side of the gap absorbs energy.