• Using different sources of?monochromatic light?demonstrate that:
  • Increasing the?wavelength?increases the?width?of the fringes
• The?angle of diffraction?of the?first minima?can be found using the equation:

• 
• ?Where:
  • θ?= the angle of diffraction (radians)
  • λ?= wavelength (m)
  • b?= slit width (m)

• This equation explains why?red light?produces wider maxima
  • It is because the?longer?the?wavelength,?λ, the?larger?the?angle of diffraction,?θ
• It also explains the coloured fringes seen when?white light?is diffracted
  • It is because?red light?(longer?λ) will?diffract more?than?blue light?(shorter?λ)
  • This creates fringes which are blue nearer the centre and red further out

• It also explains why wider slits cause the maxima to be narrower
  • It is because the?wider?the?slit,?b, the?smaller?the?angle of diffraction,?θ

Slit width and angle of diffraction are inversely proportional. Increasing the slit width leads to a decrease in angle of diffraction, hence the maxima appear narrower

Single Slit Geometry

• The diffraction pattern made by waves passing through a slit of width?b?can be observed on a screen placed a large distance away

The geometry of single-slit diffraction

Step 1: Write down the equation for the angle of diffraction

Change 3

• • The distance between the slit and the screen will also affect the width of the central fringe
  • A larger distance means the waves must travel further hence, will spread out more
  • Therefore,?moving the screen further away?would increase the fringe width