technoquest

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

QIn an aeroplane at 30,000 feet, you can often water droplets, even thought the temperature is below freezing point. How can this be?

A Water can exist as a liquid below 0 Centigrade, and often does. There are two main reasons. Impurities in water reduce its freezing temperature, which is why salt is put on roads in winter. Adding salt can lower the freezing point as far as -13oC. Pure liquid water can also exist below 0oC. For water to freeze, molecules must form the correct structure. A container, such as a cup or bowl, offers plenty of chances for this structure to form. With a small amount of water, the structure is less likely. Hence drops of liquid water can exist in the atmosphere at temperatures as low as -40oC.

Q Smoke alarms often only last for five years. What stops them working after this time? Is the radioactive source used up?

A Smoke detectors use tiny amounts of a radioactive element called americium. An electronic sensor detects the amount of radiation coming from the americium. If that suddenly drops - because smoke has got in the way - the alarm sounds. Americium has a half-life of several thousand years, so running out of radioactivity isn't a problem. The reason you are advised to replace your smoke detectors every five years is that the electronic detector inside can go wrong.

Q Salt is made of crystals, as are diamonds. Why are diamonds much harder than sugar?

A Diamond is a macro-molecular structure of carbon atoms, where each carbon is bonded to four others by sharing electrons with them in a covalent bond. Salt consists of sodium and chloride ions, but these are bonded ionically, meaning one or more electrons from one atom (in this case sodium) are "given" to the other atom in the molecule. Because ionic bonds don't involve sharing electrons between atoms, they aren't as strong as covalent bonds. This is why diamonds are stronger than salt.

Q Why are modern British copper coins (1p and 2p pieces) magnetic, whereas old ones are not?

A In 1992, the metal used to make coppers was changed from bronze to copper-plated steel. This makes them magnetic.

Q Who invented ball bearings?

A The idea of using balls as anti-friction devices was first suggested by Leonardo da Vinci in the 16th century, but, as with many of da Vinci's ideas, it wasn't put to use for a long time. In 1794, Philip Vaughn from Carmarthen got the first patent on a bearing which resembled modern ball bearings; but it wasn't until steel became economically available in the late 19th century that steel ball-bearings, like those we use now, became popular.

Q Why do batteries which are running down recover slightly if you don't use them?

A In a copper-zinc battery, a copper plate and a zinc plate sit in a dilute sulphuric acid solution. When the battery is working, tiny bubbles of hydrogen gas gradually form around the copper plate and prevent the flow of charge. When the battery is disconnected, some of the hydrogen disperses slightly, allowing the flow of electrons again for a short while.

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 submitted by e-mail to sci.net@campus.bt.com

Start your day with The Independent, sign up for daily news emails
ebooks
ebooksA special investigation by Andy McSmith
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

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

iJobs Job Widget
iJobs General

Recruitment Genius: Online Sales & Marketing Assistant

£22000 - £25000 per annum: Recruitment Genius: This UK based B2C and B2B multi...

Recruitment Genius: New Business Sales Executive - Opportunities Across The UK

£15000 - £30000 per annum: Recruitment Genius: Join a fast growing, UK based I...

Recruitment Genius: Events Consultant

£24000 - £32000 per annum: Recruitment Genius: A position has arisen for an ex...

Recruitment Genius: Injection Moulding Supervisor

£20000 - £26000 per annum: Recruitment Genius: Busy moulding company requires ...

Day In a Page

The difference between America and Israel? There isn’t one

The difference between America and Israel? There isn’t one

Netanyahu knows he can get away with anything in America, says Robert Fisk
Families clubbing together to build their own affordable accommodation

Do It Yourself approach to securing a new house

Community land trusts marking a new trend for taking the initiative away from developers
Head of WWF UK: We didn’t send Cameron to the Arctic to see green ideas freeze

David Nussbaum: We didn’t send Cameron to the Arctic to see green ideas freeze

The head of WWF UK remains sanguine despite the Government’s failure to live up to its pledges on the environment
Author Kazuo Ishiguro on being inspired by shoot-outs and samurai

Author Kazuo Ishiguro on being inspired by shoot-outs and samurai

Set in a mythologised 5th-century Britain, ‘The Buried Giant’ is a strange beast
With money, corruption and drugs, this monk fears Buddhism in Thailand is a ‘poisoned fruit’

Money, corruption and drugs

The monk who fears Buddhism in Thailand is a ‘poisoned fruit’
America's first slavery museum established at Django Unchained plantation - 150 years after slavery outlawed

150 years after it was outlawed...

... America's first slavery museum is established in Louisiana
Kelly Clarkson: How I snubbed Simon Cowell and become a Grammy-winning superstar

Kelly Clarkson: How I snubbed Simon Cowell and become a Grammy-winning superstar

The first 'American Idol' winner on how she manages to remain her own woman – Jane Austen fascination and all
Tony Oursler on exploring our uneasy relationship with technology with his new show

You won't believe your eyes

Tony Oursler's new show explores our uneasy relationship with technology. He's one of a growing number of artists with that preoccupation
Ian Herbert: Peter Moores must go. He should never have been brought back to fail again

Moores must go. He should never have been brought back to fail again

The England coach leaves players to find solutions - which makes you wonder where he adds value, says Ian Herbert
War with Isis: Fears that the looming battle for Mosul will unleash 'a million refugees'

The battle for Mosul will unleash 'a million refugees'

Aid agencies prepare for vast exodus following planned Iraqi offensive against the Isis-held city, reports Patrick Cockburn
Yvette Cooper: We can't lose the election. There's too much on the line

Yvette Cooper: We can't lose the election. There's too much on the line

The shadow Home Secretary on fighting radical Islam, protecting children, and why anyone in Labour who's thinking beyond May must 'sort themselves out'
A bad week for the Greens: Leader Natalie Bennett's 'car crash' radio interview is followed by Brighton council's failure to set a budget due to infighting

It's not easy being Green

After a bad week in which its leader had a public meltdown and its only city council couldn't agree on a budget vote, what next for the alternative party? It's over to Caroline Lucas to find out
Gorillas nearly missed: BBC producers didn't want to broadcast Sir David Attenborough's famed Rwandan encounter

Gorillas nearly missed

BBC producers didn't want to broadcast Sir David Attenborough's famed Rwandan encounter
Downton Abbey effect sees impoverished Italian nobles inspired to open their doors to paying guests for up to €650 a night

The Downton Abbey effect

Impoverished Italian nobles are opening their doors to paying guests, inspired by the TV drama
China's wild panda numbers have increased by 17% since 2003, new census reveals

China's wild panda numbers on the up

New census reveals 17% since 2003