How does light work

It turns out there are two important things about electric and magnetic fields. First, here is a wire carrying electric current over a magnetic compass. The electric current makes a magnetic field which causes the compass needle to turn. But you don't even need an electric current to make magnetic fields. It turns out that a changing electric field will also make a magnetic field.

Here is a coil of wire connected to a lightbulb no battery. When it is placed over this changing magnetic field, the changing electric field is created that drives a current. So we have a changing electric field that creates a magnetic field and a changing magnetic field creates an electric field.

Put these two ideas together and you can make two waves and electric field wave and a magnetic field wave that both make the other propagate. Electromagnetic waves don't need a medium because in a sense, they are their own medium.

First, there is the electromagnetic spectrum. You can make an electromagnetic wave of all different wavelengths - from larger than 1 meter radio waves to less than 10 picometers gamma rays - but they are still waves. Here is the common classification of the electromagnetic spectrum going from large wavelengths to small. All of these are electromagnetic waves and they all travel at the same speed the speed of light.

However, they have different interactions with matter. If you are inside, your mobile phone can still get data from a cell tower since these radio waves pass through most walls. Can you see through the walls? Visible light does not pass through most walls. X-rays mostly go through your skin, but you can't see with visible light through skin - that would just be weird.

Technically the interaction with light and matter depends on the frequency of light - but since frequency and wavelength are related, we can just talk about the wavelength. There are two ways that light could enter your eye. First, there could be a light source like a light bulb that create light. This light then travels into your eye and BOOM - your brain interprets this signal as light.

The other way more common is to see things by reflected light. Suppose you are looking at a pencil. The light from somewhere reflects off the pencil and then into your eye. But what happens if there is no light that enters your eye? What if you are in a place with absolutely no source of light? In that case, you perceive the color black. Actually, this can be a fun question. Ask someone this:. Have you ever been somewhere with absolutely no light? You might think scientists know all the answers, but light continues to surprise them.

Here's an example: We've always taken for granted that light travels faster than anything else in the universe.

Then, in , researchers at Harvard University were able to slow a beam of light down to 38 miles an hour 61 kilometers per hour by passing it through a state of matter known as a Bose-Einstein condensate. That's almost 18 million times slower than normal! No one would have thought such a feat possible just a few years ago, yet this is the capricious way of light.

Just when you think you have it figured out, it defies your efforts and seems to change its nature. Still, we've come a long way in our understanding. Some of the brightest minds in the history of science have focused their powerful intellects on the subject.

Albert Einstein tried to imagine what it would be like to ride on a beam of light. Einstein, though, is getting ahead of the story. To appreciate how light works, we have to put it in its proper historical context. Our first stop is the ancient world, where some of the earliest scientists and philosophers pondered the true nature of this mysterious substance that stimulates sight and makes things visible. The amazing thing about this historical turn of events is that the light bulb itself could hardly be simpler.

The modern light bulb, which hasn't changed drastically since Edison's model, is made up of only a handful of parts. In this article, we'll see how these parts come together to produce bright light for hours on end. Light is a form of energy that can be released by an atom. It is made up of many small particle-like packets that have energy and momentum but no mass.

These particles, called light photons , are the most basic units of light. For more information, see How Light Works. Atoms release light photons when their electrons become excited. If you've read How Atoms Work , then you know that electrons are the negatively charged particles that move around an atom's nucleus which has a net positive charge. An atom's electrons have different levels of energy, depending on several factors, including their speed and distance from the nucleus.

Electrons of different energy levels occupy different orbitals. Generally speaking, electrons with greater energy move in orbitals farther away from the nucleus.

When an atom gains or loses energy, the change is expressed by the movement of electrons.