Light is a form of radiant energy. To a scientist, "Light" refers to all electromagnetic radiation, not just the type we can see (visible light). Light is created whenever a charged particle vibrates. This produces an electric and magnetic force on all objects in the universe. This force radiates from the source at the speed of light (about 186,000 mph in a vacuum!). Light exhibits properties of waves and of particles.
Light travels as two perpendicular transverse waves, one representing the movement of the electric field and the other the magnetic field. Unlike sound, light does not require a medium to travel through. This boggled scientists for centuries and only recently (about a century ago) did they abandon the idea that there was an "ether" in space that could "carry" the light. We now know that light can travel "in vacuo"...in a vacuum.
Ways of Creating Light:
1) Heat an object up. As an object becomes hotter, it emits more light and it will produce higher energy light (cool = infrared, warm = visible light, hot = ultraviolet, crazy hot = gamma rays). Heating an object produces a continuous spectrum (there are no gaps in the colors/wavelengths). Enjoy: Black Body Radiation PhET interactive
2) Excite an atom's electrons. When they return to the ground state, they will release light of only certain colors. This will produce a spectrum of bright lines of only certain colors. Presentation/Simulation - try to understand the beginning of this.
Light travels as two perpendicular transverse waves, one representing the movement of the electric field and the other the magnetic field. Unlike sound, light does not require a medium to travel through. This boggled scientists for centuries and only recently (about a century ago) did they abandon the idea that there was an "ether" in space that could "carry" the light. We now know that light can travel "in vacuo"...in a vacuum.
Ways of Creating Light:
1) Heat an object up. As an object becomes hotter, it emits more light and it will produce higher energy light (cool = infrared, warm = visible light, hot = ultraviolet, crazy hot = gamma rays). Heating an object produces a continuous spectrum (there are no gaps in the colors/wavelengths). Enjoy: Black Body Radiation PhET interactive
2) Excite an atom's electrons. When they return to the ground state, they will release light of only certain colors. This will produce a spectrum of bright lines of only certain colors. Presentation/Simulation - try to understand the beginning of this.
Types of Light - All electromagnetic radiation is fundamentally the same thing, but we can only see a small portion of the entire spectrum. The diagrams below show the types of light from longest to shortest waves. Notice also that only certain types of light (visible and radio) can penetrate the Earth's atmosphere, and we are lucky that this is the case.
Visible Light
Let's begin by focusing on the portion of the electromagnetic spectrum that we can see - visible light. We can only see a small portion of the spectrum...most light is actually invisible to us.
As shown in the diagrams above, red light has the longest wavelength and violet light has the shortest wavelength. When long, visible wavelengths of light enter our eyes and are transmitted to our brain via electrical impulses, we perceive a red color. Conversely, when short, high energy light in the visible spectrum enters our eyes, we perceive a violet color. This our brain's way of interpreting the incoming radiation into useful information about our surroundings.
White Light contains all the colors. This was first shown by Sir Isaac Newton using a prism. Different colors are refracted (bent) different amounts, thus a prism separates light into colors.
Let's begin by focusing on the portion of the electromagnetic spectrum that we can see - visible light. We can only see a small portion of the spectrum...most light is actually invisible to us.
As shown in the diagrams above, red light has the longest wavelength and violet light has the shortest wavelength. When long, visible wavelengths of light enter our eyes and are transmitted to our brain via electrical impulses, we perceive a red color. Conversely, when short, high energy light in the visible spectrum enters our eyes, we perceive a violet color. This our brain's way of interpreting the incoming radiation into useful information about our surroundings.
White Light contains all the colors. This was first shown by Sir Isaac Newton using a prism. Different colors are refracted (bent) different amounts, thus a prism separates light into colors.
Water droplets can also refract light, causing a rainbow.
This diagram helps us visualize how a rainbow i different colors are bent are refracted at different angles, we can see the various colors in
Here is a nice double rainbow I saw in South Hero last fall. It appeared more vivid to me, but our cameras are not always as effective as our eyes in seeing details depending on the lighting conditions.
In a double rainbow, the second band of colors is formed when the light bounces off the edge of the water droplet twice! The diagram below shows how this produces a different angle for the colors, so we perceive the colors in a different part of the sky.
Since we are discussing how the atmosphere can affect colors that we see, a few questions are likely to follow...Why is the sky blue? Why are sunrises and sunsets red? Perhaps surprisingly, it has to do with a basic property of waves that also explains why you hear an approaching car's subwoofers before you hear the high pitched tweeters. When waves encounter materials, short wavelength waves are scattered more easily than long wavelengths. For sunlight that hits the atmosphere, red light passes through the atmosphere more easily while blue and purple are scattered. So the sun would actually appear a slightly different color in space because its light is not interfered with by our atmosphere. During the day, when we look away from the Sun, we see blue light that has been scattered and then reflected towards our eyes. Thus the sky appears blue. During sunrise and sunset, the light must pass through more air so more of the colors are scattered. Only the red light can penetrate, so the sun itself appears redder and the radiation illuminates clouds, making them appear red as well. Pretty! Hopefully these shots clarify these spectacular natural phenomena.
To understand the colors that we see around us, it is important to understand the difference between combining colors of light and combining colored pigments. In general, when we combine different colored lights the result gets brighter and closer to white. When we combine more pigments (like mixing paint), the result is darker and closer to black. Combining lights adds more colors to the spectra that reach our eyes, while adding pigments that absorb light subtracts pigments that we see. Hopefully the diagrams below clarify what happens when we mix the primary colors of light and pigments.
Here are a few mind blowing optical illusions...how do you think the combination of colors and patterns tricks our brains into perceiving movement? Notice also how the movement appears in the areas away from where we are focused...strange!
Another optical illusion that helps us to understand how our eyes and brains work is called an afterimage. If you stare at the picture below for a while (about a minute or more) and then look at a white space somewhere else, you will see what is known as an afterimage. The colors will appear "reversed," that is you will perceive the complementary color of those shown in the actual diagram.
Invisible Light
Let's talk now about the other types of light found on the electromagnetic spectrum that we cannot see.
Let's talk now about the other types of light found on the electromagnetic spectrum that we cannot see.
Here is the link for a great resource on scales of scientific things, such as the different wavelengths of light: htwins.net/scale2