General Physics waves_diffrac diffraction

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

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)

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

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

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

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)

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

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