Path Difference and Interference

• Drag the sources to change the path difference.
• The blue wave represent the sum of the red waves.
• Click "add phase shift" to add a phase difference of $\pi$ to a source.

With no relative phase difference:
• Constructive interference when $\Delta l = m \lambda$.
• Destructive interference when $\Delta l = (m + \frac{1}{2}) \lambda$.

With relative phase difference of $\pi$:
• Constructive interference when $\Delta l = (m + \frac{1}{2}) \lambda$.
• Destructive interference when $\Delta l = m \lambda$.

Double Slit Interference

A lab manual based on this simulation is available here.

Drag the sources and the view screen to see how the interference pattern changes. The distances can be measured by dragging the circle to a difference location.

Multi-Slit Diffraction

Drag the screen and the circle to change their positions. The phasor diagram can also be moved by dragging on the lime-colored dot.
Red/blue are used to represent long/short wavelength for illustrative purpose only. The numerical values of the wavelength in this simulation do not in fact match with the actual wavelength of visible light.
The intensity graph is normalized so the peak intensity is always the same (in reality, as the number of slits increases, the peak intensity increases as well).

Diffraction with Two Wavelengths

Illustrate how diffraction gratings (with a large number of slits) is useful in distinguishing different wavelengths. Decrease the number of slits and see how the fringes of the two sources get all mixed up and difficult to distinguish from one another.
Control: Drag the screen to change its position.
Red/blue are used to represent long/short wavelength for illustrative purpose only. The numerical values of the wavelength in this simulation do not in fact match with the actual wavelength of visible light.
The intensity graph is normalized so the peak intensity is always the same (in reality, as the number of slits increases, the peak intensity increases as well).

Single-Slit Diffraction

A lab manual based on this simulation is available here.

Drag on the barriers to change slit width. Drag the screen and the circle to change their positions. The phasor diagram can also be moved by dragging on the lime-colored dot.
Red/blue are used to represent long/short wavelength for illustrative purpose only. The numerical values of the wavelength in this simulation do not in fact match with the actual wavelength of visible light.

Rayleigh's Criterion

A lab manual based on this simulation is available here.

Drag on the barriers to change slit width. Drag the screen and the circles (light sources) to change their positions.