1. General Physics waves_diffrac diffraction

2. General Physics waves_diffrac
Objectives
Use Huygens’s principle to explain why diffraction occurs.
Describe the diffraction of waves around barriers.

3. General Physics waves_diffrac
Diffraction
A wave front passing through a barrier bends at the edges
Run at: w1 = 0.2; k1 = 0.2; ampl = 15
integral multiples (half, third, quarter) of lambda: multiply w1, k1 by 2, 3, 4
add same-lambda wave with negative amplitude
Beats: slightly vary w2 and k2 together from wave 1 values (0.22 and 0.22; 0.21 and 0.21, etc.)
Standing waves (use w of about 0.2; try w = 0.2, k = 0.1)

4. Understanding Diffraction
General Physics waves_diffrac
Understanding Diffraction
Huygens’s Principle: A wave front is composed of “wavelets”

5. Understanding Diffraction
General Physics waves_diffrac
Understanding Diffraction
Huygens’s Principle: A wave front is composed of “wavelets”
that interfere to produce the observed front

6. Single Slit Diffraction
General Physics waves_diffrac
Single Slit Diffraction
Plane waves encounter a slit in a barrier
And diffract as they pass through

7. General Physics waves_diffrac
Diffraction
Wavelets interfere to make nodes and antinodes
(ripple tank simulation)
Run at: w1 = 0.2; k1 = 0.2; ampl = 15
integral multiples (half, third, quarter) of lambda: multiply w1, k1 by 2, 3, 4
add same-lambda wave with negative amplitude
Beats: slightly vary w2 and k2 together from wave 1 values (0.22 and 0.22; 0.21 and 0.21, etc.)
Standing waves (use w of about 0.2; try w = 0.2, k = 0.1)

8. General Physics waves_diffrac
Where are the Nodes?
First minimum (node) at the angle where wave front cancels ½ slit across
Half cycle out of phase
Destructive interference
Run at: w1 = 0.2; k1 = 0.2; ampl = 15
integral multiples (half, third, quarter) of lambda: multiply w1, k1 by 2, 3, 4
add same-lambda wave with negative amplitude
Beats: slightly vary w2 and k2 together from wave 1 values (0.22 and 0.22; 0.21 and 0.21, etc.)
Standing waves (use w of about 0.2; try w = 0.2, k = 0.1)
Reach the detector at the same time D l

9. First Node Rectangular slit: sin q = l/D
Circular aperture: sin q = 1.22 l/D
Most energy is between the first nodes
A narrow aperture makes a wider dispersion
Maximum (sin q) = 1
no nodes if D < l