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
ebooksA special investigation by Andy McSmith
  • Get to the point
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: Client Services Assistant

£18000 - £20000 per annum: Recruitment Genius: A Client Services Assistant is ...

Recruitment Genius: Junior / Senior Sales Broker - OTE £100,000

£20000 - £100000 per annum: Recruitment Genius: This is an excellent opportuni...

Recruitment Genius: Duty Manager

Negotiable: Recruitment Genius: A Duty Manager is required to join one of the ...

Recruitment Genius: Team Leader

Negotiable: Recruitment Genius: A Team Leader is required to join one of the l...

Day In a Page

No postcode? No vote

Floating voters

How living on a houseboat meant I didn't officially 'exist'
Louis Theroux's affable Englishman routine begins to wear thin

By Reason of Insanity

Louis Theroux's affable Englishman routine begins to wear thin
Power dressing is back – but no shoulderpads!

Power dressing is back

But banish all thoughts of Eighties shoulderpads
Spanish stone-age cave paintings 'under threat' after being re-opened to the public

Spanish stone-age cave paintings in Altamira 'under threat'

Caves were re-opened to the public
'I was the bookies’ favourite to be first to leave the Cabinet'

Vince Cable interview

'I was the bookies’ favourite to be first to leave the Cabinet'
Election 2015: How many of the Government's coalition agreement promises have been kept?

Promises, promises

But how many coalition agreement pledges have been kept?
The Gaza fisherman who built his own reef - and was shot dead there by an Israeli gunboat

The death of a Gaza fisherman

He built his own reef, and was fatally shot there by an Israeli gunboat
Saudi Arabia's airstrikes in Yemen are fuelling the Gulf's fire

Saudi airstrikes are fuelling the Gulf's fire

Arab intervention in Yemen risks entrenching Sunni-Shia divide and handing a victory to Isis, says Patrick Cockburn
Zayn Malik's departure from One Direction shows the perils of fame in the age of social media

The only direction Zayn could go

We wince at the anguish of One Direction's fans, but Malik's departure shows the perils of fame in the age of social media
Young Magician of the Year 2015: Meet the schoolgirl from Newcastle who has her heart set on being the competition's first female winner

Spells like teen spirit

A 16-year-old from Newcastle has set her heart on being the first female to win Young Magician of the Year. Jonathan Owen meets her
Jonathan Anderson: If fashion is a cycle, this young man knows just how to ride it

If fashion is a cycle, this young man knows just how to ride it

British designer Jonathan Anderson is putting his stamp on venerable house Loewe
Number plates scheme could provide a licence to offend in the land of the free

Licence to offend in the land of the free

Cash-strapped states have hit on a way of making money out of drivers that may be in collision with the First Amendment, says Rupert Cornwell
From farm to fork: Meet the Cornish fishermen, vegetable-growers and butchers causing a stir in London's top restaurants

From farm to fork in Cornwall

One man is bringing together Cornwall's most accomplished growers, fishermen and butchers with London's best chefs to put the finest, freshest produce on the plates of some of the country’s best restaurants
Robert Parker interview: The world's top wine critic on tasting 10,000 bottles a year, absurd drinking notes and New World wannabes

Robert Parker interview

The world's top wine critic on tasting 10,000 bottles a year, absurd drinking notes and New World wannabes
Don't believe the stereotype - or should you?

Don't believe the stereotype - or should you?

We exaggerate regional traits and turn them into jokes - and those on the receiving end are in on it too, says DJ Taylor