technoquest

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

QWhat are white dwarf stars?

A White dwarfs are a small, dim stars which are reaching the end of their life. They start as normal stars, and then go through a period of intense activity near the end of their life, during which they expand and become hundreds of times larger than usual - a "red giant". Then they run out of stellar fuel, and cannot sustain their overblown size. The star then collapses, forming a super-dense white dwarf star. However, stars which are more than 40 per cent more massive than our sun do not collapse, but explode as a supernova. Our sun will end its days as a white dwarf - in about five billion years.

QWhy does electricity like to go to earth?

A The flow of electricity is a result of what is known as a potential difference. This is like a pressure difference in a water pipe. If you fix a hosepipe to a tap and turn the water on, the water flows because there's water pressure at the tap which that forces the water through the pipe - but if the hose end is closed, it won't flow. Electricity is the same. Electrons at one end of the wire have energy, while those at the other end connected to earth haven't. This creates a sort of "energy pressure" that forces the energy along the wire. Of course, for the purposes of an electrical circuit, "earth" can be defined as a point in the system with a lower potential than any other. The electrons then flow to that.

QDo ears continue to grow after maturity?

A Yes, earlobes can continue to grow, but generally once the head has stopped growing, so do the ears.

QHow do we know the age of the Earth?

A The age of the solar system is generally said to be about 4.6 billion years, but the age of the Earth is only around 4.5 billion years as it took a bit of time for the planets to form once the solar system had formed. The age of the Earth is calculated in a variety of ways. The minimum age of the Earth is given by the age of its oldest rocks - 3.8 billion years. But erosion has removed some of the earliest rocks so we know it's older than that. By dating meteorites, which haven't changed much since the birth of the solar system, we can constrain the maximum age of the Earth at 4.6 billion years. But it is the radioactive decay of certain minerals in the Earth which dates our planet more precisely - at about 4.5 billion years old.

QHow do low-radiation computer screens work?

A Computers now must comply with very strict rules on emission of electromagnetic radiation. Some computer manufacturers make a big deal about having screens that are "low radiation", but in reality they are no more low radiation than any of the other screens on the market, because they must all obey the same law. Radiation, in the form of high-frequency radio waves, is given out by computer screens because of the power they use. The less power, the less radiation. Developments in the technology used inside a computer mean that they don't need as much power as before to appear equally bright. They need 50 to 60 per cent less power now than when they were first made, so they give off 50 to 60 per cent less radiationn

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Questions for this column can be submitted by e-mail to chrisr@bss.org