Electromagnetic wave
Changing electric and magnetic fields, hand in hand, racing off into the distance.
According to Maxwell's equations, a changing electric field produces a magnetic field and a changing magnetic field produces an electric field. Each generates the other, and together they travel through space at the speed of light c. A plane electromagnetic wave is transverse: the electric field E, the magnetic field B and the direction of propagation are mutually perpendicular, E and B oscillate in phase, and their magnitudes satisfy B = E/c. The average intensity is I = E₀²/(2μ₀c).
E and cB along the propagation direction at one instant
The two curves coincide exactly: E and B are in phase, and cB equals E in magnitude.
Think about it
If the electric field amplitude is 5 V/m, what is the magnetic field amplitude?
B₀ = E₀/c = 5 / (3 × 10⁸) ≈ 1.67 × 10⁻⁸ T, or about 16.7 nT. Although the magnetic field is numerically small, it carries as much energy as the electric field.
Model assumptionsPlane harmonic wave in vacuum · linearly polarized · propagation greatly slowed on screen
Data log
Set the parameters and click “Record data”. Record several rows with different parameters to plot their relationship and fit a straight line; pause and record at different times to study how a reading changes with time.