1. The Source: An Accelerating Charge
* Key Point: The fundamental principle is that accelerating charges produce electromagnetic radiation. Shaking a charged object is a form of acceleration.
2. Electric and Magnetic Fields
* Charged Objects: A charged object creates an electric field around it. This field exerts forces on other charges.
* Movement: When the charged object moves, the electric field changes. This changing electric field induces a magnetic field.
* Acceleration: When the charged object accelerates (like shaking back and forth), both the electric and magnetic fields change rapidly.
3. The Birth of an Electromagnetic Wave
* Intertwined Fields: The changing electric and magnetic fields become intertwined. They "feed" off each other, constantly creating and reinforcing each other.
* Propagation: This self-sustaining system of changing fields propagates outward as a wave. This is the electromagnetic wave.
4. Properties of Electromagnetic Waves
* Speed: Electromagnetic waves travel at the speed of light in a vacuum (approximately 299,792,458 meters per second).
* Transverse Waves: The electric and magnetic fields in the wave oscillate perpendicular to the direction the wave travels.
* Spectrum: Electromagnetic waves come in a wide range of frequencies, from low-frequency radio waves to high-frequency gamma rays. These different frequencies have different wavelengths, and we experience them as different forms of light (visible light, infrared, ultraviolet, etc.).
Analogy: Ripples on a Pond
Imagine throwing a stone into a pond. The disturbance creates ripples that spread outward. These ripples are analogous to electromagnetic waves. The stone's impact creates a disturbance in the water, similar to how the accelerating charge creates disturbances in the electric and magnetic fields.
In Summary
Shaking a charged object creates electromagnetic waves because the acceleration of the charge causes the electric and magnetic fields around it to oscillate rapidly. These oscillating fields become intertwined and propagate outward at the speed of light.
