INTERFERENCE
Objectives
• Describe how light waves interfere with each other to produce bright
and dark fringes.
• Identify the conditions required for interference to occur.
• Predict the location of interference fringes using the equation for
double-slit interference.
Video Observation - Discussion
• https://www.youtube.com/watch?v=CAe3lkYNKt8
Waves in
Phase and
Out of Phase
Resultant Waves
Wave Length , Amplitude , node and antinode
Phase
difference
for
Interference
Two speakers 3.0 m apart are making sound with a wavelength of
48.0 cm. and v = 343 m/s? is it loud, or quiet (frequency)
If I am 2.12 m from one speaker, and 3.80 m from the other,, and
how many wavelengths difference in distance is there? is it
destructive or constructive ?
Hint : v = f 
3.5 wavelengths, destructive
Coherent Vs
Incoherent
interference
Conditions of
Interference
of light
waves
Path
Difference
for Light
Waves from
Two Slits
Equation for Interference
Sample
problem
Practice 1
• Lasers are devices that can emit light at a specific wavelength. A
double-slit interference experiment is performed with blue-green
light from an argon-gas laser. The separation between the slits is 0.50
mm, and the first-order maximum of the interference pattern is at an
angle of 0.059° from the centre of the pattern. What is the
wavelength of argon laser light?
Practice 3
• A pair of narrow parallel slits separated by a distance of 0.250 mm is
illuminated by the green component from a mercury vapor lamp (λ =
546.1 nm). Calculate the angle from the central maximum to the first
bright fringe on either side of the central maximum.