Tuesday 18 March 1997
Q These days bread isn't just made of flour and water. What else is added?
A Bakers often add their own mix of wheat and other grains to give the bread texture and flavour. Some add vitamins. In 1986 the manufacturers of the flour and wheat mixes also added a compound called creta preparate to some vitamin-enhanced breads, as a source of calcium and as a filler.
Q How do colour photocopiers work?
A The image is scanned four times - once for each of the three primary printing colours (cyan, magenta and yellow) and once for black. Using charge-coupled devices, or CCDs, which are electrical sensors that react very precisely to light, the copier assesses the brightness of the image for each colour. The paper then rolls around the drum four times as the correct amount of each coloured ink is applied.
Q What is tensile strength, and why is it important to know the tensile strength of materials?
A Tensile strength is the force needed to stretch a material until it breaks. Take bridge building: suspension bridges are built by hanging the bridge from a steel "rope" under tension. When designing the bridge it is important to know under what force the steel breaks at, to be sure the bridge will hold up.
Q Cows eat green grass. So why is their milk white?
A The colour of the food animals eat doesn't really determine the colour of what comes out - and this is especially true in a cow, where the grass is completely broken down as it passes through its four stomachs, and no longer has a colour. So the question becomes, why is milk white? This is because it's an emulsion - one liquid completely suspended in another. Milk is a fine dispersion of calcium caseinate suspended in liquid.
Q What are parachutes made of, and how long do they last?
A Silk hasn't been used in the manufacture of parachutes for 50 years. Nowadays they use rip-stop nylon, which is made of lots of tiny squares which prevent a rip from propagating along its length. A parachute will last about 10-12 years, or 100 jumps (whichever comes first) before it should be replaced. Of course, it can be damaged earlier - usually on landing. A standard person-carrying parachute requires about 100 square metres of material.
Q Last week's answer about halogen bulbs was wrong; how do they really work?
A That's true - the error was introduced during editing. Here's the right answer. A conventional light bulb, filled with an inert gas such as argon, is limited to a certain temperature: the tungsten filament gradually evaporates and condenses on the cooler glass envelope, and a very bright bulb would wear out too quickly. A halogen bulb enables the filament to run at a higher temperature, hence is brighter. Halogens - fluorine, chlorine, bromine, iodine and astatine - are highly reactive. A tungsten halide (usually tungsten iodide) is the key: it is stable at low temperature, but unstable when very hot. When the tungsten evaporates from the hot filament it forms a vapour which cools as it nears the outer glass, and reacts with the iodine to form tungsten iodide. This itself is stable until it comes into contact with the very hot filament, where it dissociates into its elements. Tungsten is redeposited on the filament, releasing iodine vapour to repeat the cycle.
You can also visit the technoquest World Wide Web site at http://
www.campus.bt.com/CampusWorld/pub/ScienceNet. Questions for this column can be sent by e-mail to firstname.lastname@example.org
- 1 What happens to your body when you give up sugar?
- 2 Ed Miliband less influential than One Direction's Louis Tomlinson by official Doncaster power list
- 3 Japanese island overrun with cats after population explodes
- 4 Delhi bus rapist blames dead victim for attack because 'girls are responsible for rape'
- 5 Have sex with your iPad thanks to the new sex toy no-one asked for
California teacher appears to have hanged herself in her classroom
The City of the Monkey God: Archaeologists claim to have found city lost for 1,000 years in remote Honduran jungle
Ed Miliband less influential than One Direction's Louis Tomlinson by official Doncaster power list
Japanese island overrun with cats after population explodes
Delhi bus rapist blames dead victim for attack because 'girls are responsible for rape'
'Jihadi John': CAGE representative storms off Sky News accusing Kay Burley of Islamophobia
Durham Free School: 'Creationism taught at' free school facing closure
Nearly 100,000 of Britain's poorest children go hungry after parents' benefits are cut
Ukip would cut billions from Scottish budget to fund English tax cuts
End of the licence fee: BBC to back radical overhaul of how it is funded
Ukraine crisis: Top Chinese diplomat backs Putin and says West should 'abandon zero-sum mentality'
£16000 - £46000 per annum: Recruitment Genius: This is an opportunity to join ...
£9 - £13 per hour: Recruitment Genius: This is a great opportunity to join a s...
£25000 - £35000 per annum: Recruitment Genius: Have you got a proven track rec...
£15000 - £18000 per annum: Recruitment Genius: This is a great opportunity for...