T-shirts which change colour are dyed using Lenco dyes. Ordinary T-shirts are certain colours because the dyes that they have been dyed with have electrons in certain positions within each atom. The position of these electrons determines the wavelength of light given off by the T-shirt. Lenco dyes are made of chemicals in which the electrons can be moved around, altering the wavelength and thus the colour of the reflected light.
Q: Who invented the light bulb?
In 1845, J Starr, an inventor in the United States, suggested using a filament of carbon as an electricity conductor enclosed in a glass bulb to produce light. In 1878, Joseph Swan, from Britain, developed a vacuum pump to remove air from the bulb so that the filament would not oxidise and burn away, but it wasn't until 1879 that Thomas Edison (of America) patented the world's first electric light bulb. Edison's bulb burned for 13.5 hours before it went out. However, Joseph Swan, from Sunderland, was the first to demonstrate an electric light bulb in December 1878 - shortly before Edison. He just didn't get round to patenting it.
Q: Why don't aircraft spin their wheels before landing to stop the wheels skidding?
When landing, an aircraft's wheels either have to spin at exactly the same speed as the aircraft or not be spinning at all otherwise the plane can skid. In order to get the wheels spinning at exactly the speed the aircraft is moving at would need a motor attached to each wheel. This would add too much weight and expense to make it worthwhile.
Q: Why don't we have solid, slash-proof tyres for cars?
When tyres were first invented they were solid. But the pneumatic tyres used today on cars make journeys smoother and more comfortable as the air inside them cushions the car from bumps. Until solid tyres can be made which will cushion the passengers as much as those filled with air, the idea of having slash- or puncture-free tyres will remain just an idea. Q: Why is glass transparent?
Normally, when light hits something it excites the electrons within its atoms and these then de-excite giving out light of a certain wavelength, which relates to the colour that we see. Atoms have levels and the electrons are excited between them. With transparent materials, these levels are so far apart that light does not possess enough energy to excite the electrons and so the light passes straight through without interacting with the material.
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