Questions and answers provided by Science Line's Dial-a-Scientist on 0345 600444

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:// Questions for this column can be sent by e-mail to

Start your day with The Independent, sign up for daily news emails
Barn owls are among species that could be affected
charity appeal
Sarah Silverman (middle) with sister Reform Rabbi Susan Silverman (right) and sister actress Laura Silverman (left) at Jerusalem's Western Wall for feminist Hanuka candle-lighting ceremony
peopleControversial comedian stages pro-equality Hanukkah lighting during a protest at Jerusalem's Wailing Wall
Arts and Entertainment
The Bach Choir has been crowned the inaugural winner of Sky Arts’ show The Great Culture Quiz
arts + ents140-year-old choir declared winner of Sky Arts' 'The Great Culture Quiz'
After another poor series in Sri Lanka, Alastair Cook claimed all players go through a lean period
cricketEoin Morgan reportedly to take over ODI captaincy
ebooksA year of political gossip, levity and intrigue from the sharpest pen in Westminster
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Recruitment Genius: Finance Director

£65000 - £80000 per annum: Recruitment Genius: Finance Director required to jo...

Recruitment Genius: Medico-Legal Assistant

£15000 - £25000 per annum: Recruitment Genius: This is a unique opportunity fo...

Ashdown Group: (PHP / Python) - Global Media firm

£50000 per annum + 26 days holiday,pension: Ashdown Group: A highly successful...

The Jenrick Group: Quality Inspector

£27000 per annum + pension + holidays: The Jenrick Group: A Quality Technician...

Day In a Page

Homeless Veterans appeal: 'You look for someone who's an inspiration and try to be like them'

Homeless Veterans appeal

In 2010, Sgt Gary Jamieson stepped on an IED in Afghanistan and lost his legs and an arm. He reveals what, and who, helped him to make a remarkable recovery
Could cannabis oil reverse the effects of cancer?

Could cannabis oil reverse effects of cancer?

As a film following six patients receiving the controversial treatment is released, Kate Hilpern uncovers a very slippery issue
The Interview movie review: You can't see Seth Rogen and James Franco's Kim Jong Un assassination film, but you can read about it here

The Interview movie review

You can't see Seth Rogen and James Franco's Kim Jong Un assassination film, but you can read about it here
Serial mania has propelled podcasts into the cultural mainstream

How podcasts became mainstream

People have consumed gripping armchair investigation Serial with a relish typically reserved for box-set binges
Jesus Christ has become an unlikely pin-up for hipster marketing companies

Jesus Christ has become an unlikely pin-up

Kevin Lee Light, aka "Jesus", is the newest client of creative agency Mother while rival agency Anomaly has launched Sexy Jesus, depicting the Messiah in a series of Athena-style poses
Rosetta space mission voted most important scientific breakthrough of 2014

A memorable year for science – if not for mice

The most important scientific breakthroughs of 2014
Christmas cocktails to make you merry: From eggnog to Brown Betty and Rum Bumpo

Christmas cocktails to make you merry

Mulled wine is an essential seasonal treat. But now drinkers are rediscovering other traditional festive tipples. Angela Clutton raises a glass to Christmas cocktails
5 best activity trackers

Fitness technology: 5 best activity trackers

Up the ante in your regimen and change the habits of a lifetime with this wearable tech
Paul Scholes column: It's a little-known fact, but I have played one of the seven dwarves

Paul Scholes column

It's a little-known fact, but I have played one of the seven dwarves
Fifa's travelling circus once again steals limelight from real stars

Fifa's travelling circus once again steals limelight from real stars

Club World Cup kicked into the long grass by the continued farce surrounding Blatter, Garcia, Russia and Qatar
Frank Warren column: 2014 – boxing is back and winning new fans

Frank Warren: Boxing is back and winning new fans

2014 proves it's now one of sport's biggest hitters again
Jeb Bush vs Hillary Clinton: The power dynamics of the two first families

Jeb Bush vs Hillary Clinton

Karen Tumulty explores the power dynamics of the two first families
Stockholm is rivalling Silicon Valley with a hotbed of technology start-ups

Stockholm is rivalling Silicon Valley

The Swedish capital is home to two of the most popular video games in the world, as well as thousands of technology start-ups worth hundreds of millions of pounds – and it's all happened since 2009
Did Japanese workers really get their symbols mixed up and display Santa on a crucifix?

Crucified Santa: Urban myth refuses to die

The story goes that Japanese store workers created a life-size effigy of a smiling "Father Kurisumasu" attached to a facsimile of Our Lord's final instrument of torture
Jennifer Saunders and Kate Moss join David Walliams on set for TV adaptation of The Boy in the Dress

The Boy in the Dress: On set with the stars

Walliams' story about a boy who goes to school in a dress will be shown this Christmas