This simulation shows the electric field. Bright is positive, dark is negative, gray is zero. A single oscillating source at the center sends circular wavefronts outward at a finite speed.
Tap the Field button toPress F to switch to |H| and see the magnetic field. At any fixed point, E and H peak at different moments: when E crosses zero, |H| is at its maximum. Energy oscillates between the two fields as the wave propagates.
The source oscillates at a fixed frequency f. The distance between consecutive peaks is the wavelength λ. They're locked together by the wave speed:
c = f × λ
Since c is fixed by the medium, raising the frequency shortens the wavelength. Drag the slider to see the wavelength change as you vary the frequency.
The equations governing these waves are linear, which means that when two waves overlap, the fields add point by point.
Where peaks coincide, the field doubles (constructive interference). Where a peak meets a trough, they cancel (destructive interference).
In this simulation, two sources oscillate side by side. The radiating lines of reinforcement and cancellation come entirely from basic addition.
Wider spacing gives narrower fringes. We'll come back to this in Chapter III.
Far from a point source, the wavefronts flatten out. A plane wave is the idealization: uniform phase across each wavefront, propagating in one direction.
In this simulation, a line of point sources along the left edge, all oscillating in phase, approximates one. Their overlapping circular wavefronts superpose into a flat front. Most of the later chapters start with a plane wave hitting some structure.
Here, we have an empty grid. Touch the simulationMove your cursor over the simulation to make waves.
Move slow for a focused disturbance. Move fast to lay down a broad wavefront. Try making two quick taps near each other and watch the interference pattern form.