Interference

Understandings:

• Superposition
• Path difference
• Interference patterns

Applications and skills:

• Sketching and interpreting the superposition of pulses and waves

Guidance:

• Students will be expected to calculate the resultant of two waves or pulses both graphically and algebraically
• Students should have the opportunity to observe (diffraction and) interference patterns arising from more than one type of wave
• Students should be introduced to interference patterns from a variety of coherent sources such as (but not limited to) electromagnetic waves, sound and simulated demonstrations

Understandings:

• Double-slit interference
• Young’s double-slit experiment
• Modulation of two-slit interference pattern by one-slit diffraction effect
• Multiple slit and diffraction grating interference patterns

Applications and skills:

• Quantitatively describing double-slit interference intensity patterns
• Qualitatively describing two-slit interference patterns, including modulation by one-slit diffraction effect
• Investigating Young’s double-slit experimentally
• Sketching and interpreting intensity graphs of double-slit interference patterns
• Solving problems involving the diffraction grating equation

Guidance:

• Students will not be expected to derive the double-slit equation
• Diffraction grating patterns are restricted to those formed at normal incidence

Understandings:

• Thin film interference

Applications and skills:

• Describing conditions necessary for constructive and destructive interference from thin films, including phase change at interface and effect of refractive index
• Solving problems involving interference from thin films

Guidance:

• The treatment of thin film interference is confined to parallel-sided films at normal incidence
• The constructive interference and destructive interference formulae listed below and in the data booklet apply to specific cases of phase changes at interfaces and are not generally true