# How Light Starts: Exploring Maxwell's Equations

• stringbean
In summary: This is how light can propagate through space. It's not instantaneous though, it takes time for the energy to propagate. This is why you see the same light coming from a lightbulb even if the bulb is moved a long way from the source. The speed of light is the limit to how fast the energy can travel.In summary, an electric and magnetic wave can be self supportive and vary with time. The derivation of the wave equation from Maxwell's equations is suggestive if not proof.
stringbean
I've been reading my physics book about Maxwell's equations. It makes sense to me that an electric and magnetic wave could be self supportive and vary with time. What doesn't make sense to me is why it should travel through space, in other words vary in space. The derivation of the wave equation from Maxwell's equations is very suggestive if not proof. I just want to know how you could know where the wave begins and what starts it. And if non varying electric and magnetic fields start it and are present far away instantaneously, why don't the electromagnetic waves start far away as well. The book I'm reading only explains it by saying that the magnetic and electric fields start the waves nearby and don't give a reason why they should think that. Do all changes in values of electric or magnetic fields have to propagate out at the speed of light or do places far away change instantaneously. Maybe I should differentiate between electric fields caused by changing magnetic fields from electric fields caused by charges but electrodynamic books don't seem to differentiate.

The easiest way to think of this is to consider a standard dipole antenna. In a dipole antenna you have a current sloshing back and forth inside the antenna, but the current can't leave the ends of the antenna, so actually the amplitude of the current is highest in the middle and zero on the ends. This spatially and temporally varying current is the source of a spatially and temporally varying magnetic field. Similarly with charge and the e-fields, except that the amplitude of the charge is highest on the ends.

Pretty much all waves are caused by an oscillation between kinetic energy and potential energy. There is a storage of energy in one form and release in another that are complimentary and this implies some sort of spring (as a crude physical analogy). Or actually 2 springs operating in tandem.

The loading of the spring in the case of light is the build up (compression in terms of volume) of localized electric energy and then its release. Concurrently there is a release of magnetic energy followed by a build up in a way that both lag each by 90 degrees (or minus 90 degrees) when plotted over time.

## 1. How does light start?

Light is an electromagnetic wave that is created by the acceleration of charged particles, such as electrons. This acceleration produces a changing electric and magnetic field, which propagates through space as light.

## 2. What are Maxwell's equations?

Maxwell's equations are a set of four mathematical equations that describe the behavior of electric and magnetic fields. They were developed by James Clerk Maxwell in the 19th century and are fundamental to understanding the properties of light.

## 3. What is the relationship between Maxwell's equations and light?

Maxwell's equations explain how electric and magnetic fields interact and give rise to electromagnetic waves, including light. They describe the propagation of light and its behavior when interacting with matter.

## 4. How do Maxwell's equations impact our understanding of light?

Maxwell's equations provide a comprehensive framework for understanding the properties and behavior of light. They have revolutionized our understanding of light and have led to many practical applications, such as the development of communication technologies and medical imaging.

## 5. Can Maxwell's equations be simplified or applied to other phenomena?

Maxwell's equations can be simplified for specific scenarios, such as in the study of static electric and magnetic fields. They can also be applied to other phenomena, such as sound and fluid dynamics, by making some modifications to the equations and variables.

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