Diffraction

Define diffraction

The bending and spreading of waves as they pass through a narrow gap or around an obstacle

Define refraction.

The bending of a wave when it passes at an angle from one medium into another, caused by a change in the waves speed.

How much diffraction output happens when wavelength is greater, smaller and equal to slit width?

Slit width> wavelength, diffraction is unnoticeable, central maximum is narrower (because less diffraction-spreading out) and more intense

Slit width< wavelength, little diffraction- mostly reflects back

Wavelength= slit width, most diffraction and you’ll get a diffraction pattern

How can you observe a clear diffraction pattern?

You need to use monochromatic, coherent light source (laser)

Describe the light diffraction pattern using a laser

Central bright fringe (central maximum)

Alternating dark and bright point sure to constructive and destructive interference

What happens when you diffract white light through a narrow single slit?

A spectra of colours is created (output)

Because white light is a mix of different colours with different wavelengths being diffracted by different amounts

No fringes are visible, only a spectra of different colours

What happens to intensity of the light when wavelength is greater, equal to, smaller than slit width

Slit width> wavelength, intensity is at its highest at central maximum

Slit width< wavelength, intensity is at its lowest (total spreading)

Slit width=wavelength, intensity is medium, (widest visible pattern of diffraction)

Define intensity

The power per unit area

Measure brightness

Why at the central maximum are there more photons per unit area?

At the central maximum intensity is highest ( brightest part)

Increasing intensity means increasing number of photons per second