properties of Light
- Emission:
- Light that is emitted from the source means that it is produced, discharged and radiated out.
- Transmission:
- Transmission means that it goes through - meaning through a medium or material. As it's transmitted through the material, the material may scatter, absorb, or fully allow it to go through without any hindrance. As light interacts with this material, we say instead that this material is either transparent, translucent or opaque.
Objects vary in how they transmit light.
- Transparent objects allow light to travel through them.
- Materials like air, water, and clear glass are called transparent.
- When light encounters transparent materials, almost all of it passes directly through them. Glass, for example, is transparent to all visible light.
- With transparent materials, you can see both a light and an image, because the light is not scattered or absorbed.
- Translucent objects allow some light to travel through them.
- Materials like frosted glass and some plastics are called translucent.
- When light strikes translucent materials, only some of the light passes through them. The light does not pass directly through the materials. It changes direction many times and is scattered as it passes through. Therefore, we cannot see clearly through them and objects on the other side of a translucent object appear fuzzy and unclear.
- With translucent materials, you can see light, but you cannot see an image because the light is scattered.
- Notice with the image below that light is not able to transmit as a single line, but rather it spread out as the light exited the material? That's called scattering.
Opaque objects block light from traveling through them.
- Most of the light is either reflected by the object or absorbed and converted to thermal energy.
- Materials such as wood, stone, and metals are opaque to visible light.
- With opaque materials, you can see neither light or an image.
What you see here is very similar to how X-ray's work. X-ray's are a type of light that you and I cannot see. But how it works, X-ray's are transmitted through your body and onto a screen that is sensitive to X-rays. However, your bones absorb the emitted X-ray light that is transmitted through your body. So what you see is the shadow casted by your bones onto the screen behind you. On this lightbulb, I'm shining a green laser through a white light bulb. The filament absorbs the green light and casts a shadow on the other side of the light bulb.
Reflection:
- Happens when light stays in a medium, and bounces off the surface of another medium back into the original medium.
Refraction:
- Happens when light transmits through one medium and into another medium and is bent.
LIGHT & MATTER INTERACTION
- Scatter:
- This is when light hits the medium and it goes in multiple directions.
- One type of scattering is when the light goes through the material and scatters on the other side. (Examples include the laser light below and the blue and violet light rays when they hit our atmosphere - this is why the sky is blue).
- The other type of scattering is when the light does not go through the material, but reflects off the surface in all different directions.
- This is when light hits the medium and it goes in multiple directions.
- Snow both reflects, refracts & scatters light, which is why it appears white to our eyes in the mid day sun. As the light hits the surface of the snow, it reflects and scatters, which is why it doesn't look clear - but white to our eyes.
- In addition, it also scatters and refracts through the microscopic ice crystals below the surface, but then make their way back to the surface and refract the light back to your eyes, which again, is doing it to the entire visible light spectrum, which is why it appears white to your eyes.
Translucent materials scatter the light as it transmits through. That's why you are able to see light, but not an image.
The reason why the sky looks blue is because the air scatters the blue light - while all other colors transmit through it.
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Scattered light as it goes through the material.
Scattered light as it reflects off the surface.
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What allows you to see the beams of laser light is due to scattering. Without the small particles suspended in the liquid water, you would not be able to see the laser (light).
Dispersion:
- This is when light is separated based on its wavelength. When this happens, you'll see what the spectrum of what makes white light.
Filters v. Pigments:
- Transmission: This is when light goes through the medium.
- Absorption: This is when light is not reflected or transmitted through the medium, rather, light energy is converted into thermal energy when it is absorbed.
- This is why black materials feel much hotter in the sun than white objects.
As you can see here, the red filter on the CFL light bulb emits mostly red light, with just a hint of some other colors.
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Here, you can see the red laser transmit through the raspberry Jell-o, which is reddish. When we tried the green laser, it got absorbed rather quickly - even though it was much more powerful.
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Here, you can see that the green filtered CFL light bulb emits mostly green, but it also emits some blue and a tiny amount of yellowish orange.
Here, you can see that the green filtered CFL light bulb emits mostly green, but it also emits some blue and a tiny amount of yellowish orange.
Other properties of light
Energy & the Light Spectrum |
Light & Properties of Light |
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Our eyes perceive high amplitude as bright light. The brighter it is, the more energy it has.
Our eyes perceive low amplitude as dim light. The dimmer light is, the less energy it has.
Our eyes perceive high frequency as violet (though the frequency could go much higher - but would be invisible to our eyes).
Our eyes perceive low frequency as red (though the frequency could go much lower - but would also be invisible to our eyes).
Violet has more energy than red does because it has a higher frequency.
Our eyes perceive low amplitude as dim light. The dimmer light is, the less energy it has.
Our eyes perceive high frequency as violet (though the frequency could go much higher - but would be invisible to our eyes).
Our eyes perceive low frequency as red (though the frequency could go much lower - but would also be invisible to our eyes).
Violet has more energy than red does because it has a higher frequency.
Notes for next year:
- Mediums
- elasticity of mediums
- lengths and materials
- Energy (LLL, Shhh)
- Light Spectrum
- Light properties
- Emission, Transmission, absorption, reflection
- Transparent, Translucent, Opaque