3.3.2.1
Interference 
The concept of path difference
and coherence.


AT i Investigation of twosource interference with sound, light and microwave radiation. 
The laser as a source of
coherent monochromatic light used to demonstrate interference and diffraction 
Comparison with nonlaser light;

Students will not be required to describe how a laser works. 
Students are expected to show awareness of safety issues associated with using lasers. 
Young's doubleslit experiment: the use of two coherent sources or the use of a single source with double slits to produce an interference pattern.
The appearance of the interference
fringes produced by a double slit system 
Requirements of two source and
single source doubleslit systems for the production of fringes.

where
w is the fringe spacing and
s is the slit separation 
Required practical 2: Investigation of interference effects to include the Youngâ€™s slit experiment and interference by a diffraction grating. 
Production of interference pattern using white light. 



Students will be expected to describe and explain interference produced with sound and electromagnetic waves. 


Appreciation of how knowledge and understanding of nature of electromagnetic radiation has changed over time 
3.3.2.2 Diffraction 
Appearance of the diffraction pattern from a single slit using monochromatic and white light. 
Qualitative treatment of the variation of the width of the central diffraction maximum with wavelength and slit width.
The graph of intensity against angular separation is not required. 


The plane transmission diffraction
grating at normal incidence 
Use of the spectrometer will not be tested.
Optical details of the
spectrometer will not be required. 


Derivation of the diffraction grating
equation 
Applications; e.g. spectral analysis of light from stars. 
Where n is the order number. 
3.3.2.3 Refraction at a plane surface

Students should recall that the refractive index of air is approximately 1.

Candidates are not expected to
recall methods for determining refractive indices. 
Refractive index of a substance
s:

Snell's Law of refraction at a boundary 
for a boundary between two different
substances of refractive indices n_{1} and n_{2} 


Total internal reflection 
including calculations of the critical
angle at a boundary between a substance of refractive index
n_{1} and a substance of lesser refractive
index n_{2} or air; 
Simple treatment of fibre optics including function
of the cladding with lower refractive index around central
core  limited to step index only;
Material and modal dispersion.
Application to
communications.

Students are expected to understand the principles and consequences of pulse broadening and absorption. 