Diffraction is the bending of waves around obstacles or spreading out as they pass through an opening. Think of it like when water ripples meet the edge of a rock; they flow around it!

• Wave Passing an Edge (Fig 15(a)): Waves pass the edge and form a 'quarter-circle' of new waves.
• Obstacle in the Way (Fig 15(b)): When a wave hits an obstacle, it continues on either side and spreads behind it. Imagine it’s like a double version of the previous situation.

• Francesco Grimaldi
  • Italian priest.
  • One of the first to describe diffraction in 1665.
  • Noticed funky shadows behind a narrow rod. Instead of just a shadow, he saw light spread out with cool bright and dark fringes on the edges.
• Bonus Fact: Leonardo da Vinci might’ve noticed this even before Grimaldi!

• Diffraction
  • Bending/spreading of waves around objects or openings.
  • Only the amplitude changes along the wave.
• Refraction
  • Bending of waves due to a change in speed, which also changes its wavelength. Imagine a pencil in a glass of water – it looks bent, right? That’s refraction.
  • Only the wave frequency remains the same.