single slit diffraction

Question 1

Explain what happens in single slit diffraction.

Answer 1

• light diffracts as it passes through the slit.
• this results in interference between different paths of light
• creating maxima & minima on the far screen

Question 2

Describe the intensity graph for single slit diffraction.

Answer 2

central fringe - high intensity & twice the width
all other fringes - decreases in intensity

Question 3

State the equation for the width of the central fringe.

Answer 3

W = 2Dλ/a

Question 4

State what happens when white light diffracts through a single slit.

Answer 4

• a high intensity white central fringe
• outer rainbow fringes with much lower intensity
• blue to red (centre to outer)

Question 5

Explain why the fringes of a single slit diffraction of white light produce a rainbow effect.

Answer 5

→ white light consists of light of many wavelengths
→ each wavelength diffracts by different amount
→ red light = longest λ ∴ diffracts most
→ blue light = shortest λ ∴ diffracts least
(red light will be on the ‘outside’ of each fringe, furthest away from centre)

Question 6

State two things which affect the width of the central maximum.

Answer 6

• slit width → bigger width = less diffraction so narrow maximum & higher intensity
• wavelength → bigger λ = more diffraction so wider maximum, lower intensity

Question 7

Describe the diffraction pattern for a monochromatic, coherent light source.

Answer 7

• high intensity central fringe (twice the width)
• lower intensity fringes on either side