Demonstrating Interference

• What is the ideal equipment to analyze diffraction and intensity patterns?

  Lasers
• What type of light does a laser produce?

  Coherent monochromatic light
• Why are lasers suitable for analyzing diffraction patterns?

  They produce coherent and monochromatic light
• What are the components of a laser diffraction pattern on a screen?

  • Areas of constructive interference (bright fringes)
  • Areas of destructive interference (dark fringes)
• What type of light do filament bulbs and sodium lamps produce?

  Non-coherent white light
• What can high-energy laser beams cause?

  Permanent eye damage or blindness
• What precautions should be taken when using lasers?

  • Never look directly at a laser
  • Don’t shine the laser at people
  • Avoid reflections into eyes
  • Wear laser safety goggles
  • Place a warning light outside
  • Stand behind the laser
• What is a precaution to take when using lasers?

  Place a ‘laser on’ warning light
• How can two-source interference be demonstrated using sound?

  With two speakers emitting coherent sound
• What type of waves are sound waves?

  Longitudinal waves
• What occurs during constructive interference of sound waves?

  Compressions and rarefactions line up

  
• What happens during destructive interference of sound waves?

  Compression lines up with rarefaction
• What technology uses destructive interference of sound waves?

  Noise-cancelling headphones
• How can two-source interference for microwaves be detected?

  With a moveable microwave detector
• What is the relationship between intensity and amplitude of a wave?

  • Intensity is proportional to energy transferred
  • Intensity is proportional to the square of amplitude
• What is the formula relating intensity and amplitude?

  I ∝ A²
• What does I represent in the intensity formula?

  Intensity of the wave in W/m²
• What does A represent in the intensity formula?

  Amplitude of the wave in meters
• How do you calculate the wavelength of a sound wave?

  Using the wave equation: v = fλ
• What is the wavelength of a sound wave with frequency 280 Hz?

  $1.2 \text{ m}$
• What is the condition for destructive interference?

  Path difference = $\frac{(n + 1)}{2} \lambda$
• What is the shortest path difference for destructive interference when n = 0?

  $0.6 \text{ m}$
• How many quiet spots does the student hear in 3.0 m?

  3 quiet spots