initiation and propagation

Electric-charge accelerations start electromagnetic waves {wave initiation} {initiation, wave}, because force makes radial electric field have transverse component adjacent to charge. Transverse component travels outward along electric-field line {wave propagation} {propagation, wave}, because electric-field (and magnetic-field) changes interact at light speed, because electromagnetic force is strong. Waves travel away from charges, because all energy travels outward, so no energy is left behind, and only wave leading edge (wave front) exists at any time. Wave has kinetic energy directly proportional to force that caused charge acceleration.

charge: stationary

Stationary charge makes constant electric field and no magnetic field. See Figure 1.

charge: moving

Charge moving at constant speed makes moving electric field and constant magnetic field. See Figure 2. Magnetic field is perpendicular to electric field, because magnetic field comes from relativistic length contraction that causes increased charge density along charge-motion direction, which observers see from side.

charge: acceleration

Accelerating charge increases current, because charge speed increases. Increasing current makes increasing magnetic field. Accelerating charge makes faster moving electric field. See Figure 3. (Decelerating charge decreases current, decreases magnetic field, and makes slower moving electric field.)

initiation

As charge accelerates, electric and magnetic fields accelerate, and magnetic field increases. See Figure 4.

propagation

Electric-field (and magnetic-field) change cause magnetic-field (and electric-field) gradient, by Maxwell's laws, so electric and magnetic fields interact. Interaction is at light speed. See Figure 5.

When induced electric field and magnetic field reach far-away test charge, electric-field vertical component accelerates test charge. See Figure 6.

When induced electric field and magnetic field pass far-away test charge, test charge continues at constant velocity. See Figure 7.

propagation: direction

Electromagnetic-induction is only at wave front, because all energy is there. Behind wave front, electric and magnetic fields return to zero, as fields, coming from many points with all phases, cancel. Waves propagate outward from accelerated charge, because electromagnetic-induction electric and magnetic fields behind have all phases and cancel.

propagation: no medium

Electromagnetic waves can propagate through empty space, because electric and magnetic fields are their own medium.

propagation: induction rate and wave speed

Electric-force strength determines electromagnetic-induction rate, which is light speed. Material electric charges, relativistic apparent electric charges, other electric fields, and other magnetic fields exert force on electromagnetic waves, and so reduce electromagnetic-wave speed.

Unaccelerated Charge Makes No Electromagnetic Wave

Unaccelerated moving charge makes moving constant electric field and constant concentric magnetic field. See Figure 4. No acceleration makes no force, so fields stay constant. Only radial force affects test charge, so it has no transverse motion.

Charge Acceleration Makes Traveling Electric Field

See Figure 5. Collision, gravity, or electric force can accelerate charge. Acceleration makes force, so fields change. Acceleration is transverse to radial electric-field line, so test charge has transverse motion. See Figure 6.

pure electric waves

There are no pure electric non-magnetic waves, because waves require electric-field changes, which always make transverse relativistic electric fields, which are magnetic fields. There are no pure magnetic non-electric waves, because waves require magnetic-field changes, which always make transverse relativistic electric fields.