Part 1 - Infra-Red
Did you know that the camera on your mobile phone can "see" things that your eyes can't?
- A TV remote control handset
- A mobile phone camera or webcam
Get your camera so that you can see the picture it makes either on your phone, or on your computer screen.
Now point the end of the remote control at the lens of the camera and press one of the buttons to change the channel. What do you see on the camera screen?
What should happen?
If all has gone to plan, your remote control should look like its emitting bright, white light - but light that you can't see with your eyes! This is because the silicon sensors in the camera respond to a wider range of frequencies of light than our eyes can.
It's even better in the dark! You can use it for night-vision: Here's a biscuit (very useful to be able to see biscuits in the dark, of course).
Some questions for you to answer:
- What else do you think might produce infra-red light? Well, what are you waiting for - test it! That's what science is about!
- Some digital cameras - generally more expensive ones - don't show infra-red light, though they use the same silicon technology. How do you think the camera achieves this, and why would you want to?
- Why do you think the light appears as white on the camera screen?
- Did you know... our eyes are sensitive to a more shades of green than any other colour? This is why night vision goggles display things in green. Why do you think our eyes might have developed like this?
The Light Fantastic II - Visible Light
- A handful of glow-sticks (bendy necklace/bracelet ones are best)
- A mug of ice-cold water
- A mug of hot water
Crack your bendy glow-stick to get it going and then dipping one end in the ice-cold water and the other in the hot water.
What should happen?
Leave it there for a few moments and then have a look - the cold end will be really dim and the hot end will be ablaze! Which end do you think would glow longest?
How does it work?
The light we see can be produced in a number of different ways. Very hot things glow brightly (think of the sun or the filament of a traditional light-bulb), and visible light is also produced by certain 'cold' chemical reactions. Some animals, such as fireflies, have evolved to use these chemical reactions to glow in the dark and signal to each other. Glow sticks - the sort you can buy for Halloween parties - also work by such 'luminescence' reactions. And like any other chemical reaction, the higher the temperature the faster the reaction runs and so the more light is produced.
The Light Fantastic III - Ultra-Violet
- One ultra-violet lamp - you can get hand-held battery operated ones for around £10. Or you can use a ultra-violet key ring
- Random objects around your house
Take your UV lamp or key ring exploring around the house on a dark evening and see what you can find fluorescing. Try:
- Tonic water - really!
- Clothes washing powder (why do you think this would have fluorescent dyes added? Think about what effect it would have when you wear a freshly-washed white shirt outside in the sun).
- Post-it notes and highlighter pens
- Bank notes (what secret feature only becomes visible under UV light? Why do you think that might be put on bank notes?)
How does it work?
Ultra-violet light (UV) is another kind of invisible light - it is like the opposite of infra-red, and has a wavelength too short for our eyes to be able to see. But because UV light is so energetic it is very good at getting certain kinds of molecules all excited, so that after absorbing the UV they quickly give off the extra energy as visible light. This is called 'fluorescence', and when invisible UV light is converted into light we can see it has the effect of making things appear to mysteriously glow in the dark.