YOU ARE LEARNING:
Our primary source of ultraviolet radiation comes from the Sun. It is what tans skin as well as causes sunburns. It is also responsible for fluorescent objects.
In this lesson we will look at ultraviolet rays. Which of following electromagnetic waves have lower frequencies than UV rays?
You can select multiple answers
What do you think the primary source of UV radiation is on Earth?
The primary source of UV radiation on Earth comes from the Sun.
Sun beds (that some people use for tanning) use artificial UV radiation.
How can UV light harm us?
Are we protected from UV radiation from the Sun when it is cloudy?
Most clouds block some UV rays, but some clouds can also enhance the intensity of the UV rays. When high clouds refract UV rays and lower clouds reflect them, it can significantly increase the UV levels on the ground. This effect can be increased by haze, fog, and especially snow. So remember suntan lotion on your skiing trip!
UV radiation is what gives people a tan, but it can also cause serious damage to our skin. This is why it is very important to wear sun protection to protect our eyes from blindness and our skin from burning. When yous skin burns, it increases the risk of skin cancer.
There are 3 types of UV radiation with varying levels of energy.
UVA, UVB and UVC
Which one of the 3 types of UV radiation do you think has medium frequency and can cause severe sunburn and damage to cells?
So UVB has medium frequency and can cause severe sunburn and damage to cells. Which one do you think has a high frequency and causes severe damage to cells?
UVC actually gets absorbed by the ozone layer protecting Earth.
This means that UVB is the radiation we have to think about when we make suncream.
To sum up
UVA has a low frequency and has weaker effects than UVB. UVB has a medium frequency and causes severe sunburn and damage to cells UVC has a high frequency and causes severe damage to cells.
High energy UV rays are the first type of ionising radiation in the EM spectrum, along with X-rays and gamma radiation. All the other waves in the EM spectrum are non-ionising.
An ion is an atom or molecule which has either a positive or negative charge (not neutral). What do you thing ionising radiation might mean?
So UV rays have sufficient energy to detach electrons from atoms or molecules.
This is what makes them more dangerous than any lower frequency electromagnetic radiation. It is the ability to ionise that can cause damage to skin cells and lead to cancer.
UVC radiation can also be used to sterilise water. How, do you think?
Some chemicals have a property called fluorescence.
What does it mean that an object is fluorescent?
What do you think is true of fluorescent paint?
Fluorescence happens when a chemical absorbs UV radiation, and then re-emits the energy as visible light.
This is how we can make things glow in the dark! They appear bright because they are emitting light.
Fluorescent light bulbs make use of fluorescence to be more energy efficient.
They have a layer of phosphorus covering the bulbs which they use to generate UV radiation.
What does the phosphorous do with all the energy that it absorbs from the UV radiation?
A) Nothing B) Re-emits it as UV light C) Re-emits it as visible light
We can create materials, like ink, which can only be seen under UV light.
This is useful for security marking. By including images or words in bank notes and passports that can only be seen with a UV black-light, we can see if a bank note or a passport is forged (fake). If it does not include the UV sensitive elements, it's a fake.