Last week Derek in Belgium asked a question about fluorescent lights, but we didn’t know what that period of time was to make switching off a light more efficient than leaving it on.

I have to say a very big thank you to Shia Frederick and also to Kurt Challetts who both found me the answer and they’ve sent me some references.  Based on experimentation they have concluded that – these references they’ve sent me – a fluorescent light uses as much energy getting started as it des to run for 23.3 seconds.  In other words, that is a bit of a myth about leaving it on for very long.  If you’re going to be in the room and gone for less than 23.3 seconds there’s no point it on, basically.  You might as well turn it off because it uses not very much more energy.  To put that in comparison, an LED has to run for 1.28 seconds before it uses as much energy.  The good old-fashioned incandescent lamp: 0.36 seconds before it’s used as much energy it does running as it does to turn it on.

On a fundamental minute scale iron, nickel and cobalt atoms have more electrons orbiting in one direction than the other.  This means they produce little, tiny currents like electromagnets.  With ferromagnetic things like iron, nickel and cobalt – these tend to like lining up into areas.  Normally if you just take these areas, the north poles of these little areas will attract south poles of other little areas.  They’ll all wind up going into circles and ovals in magnetism.  If you put them in a strong magnetic field they’ll all line up.  Normally with iron, if you take the magnetic field off, most of them will realign and then all the rest more randomly.

They get all jiggled up and end up pointing in random directions again. With very strong magnets, like rare earth magnets, the structure of the alloy tends to make it very hard to change the direction of the magnetic field.  This means that more of them stay lines up, and you get a stronger magnet.

You’re on the right lines there, George. The reason is that if you think of a heart as almost a sphere and the volume of a sphere is given by the mathematical formula 4/3πr3. That’s the volume of blood that a heart could hold. You could work out how much output’s coming out of your heart by multiplying the number of times per minute the heart beats (the heart rate) by what’s called the stroke volume (how much blood the heart squeezes out with every beat). Given that a heart that’s small, instead of it just decreasing its volume by a small amount when you shrink the heart a bit it will actually decrease the volume of blood proportionately by the radius cubed. For every shrinkage of the heart, if the heart gets smaller and smaller – in fact there’s a very big decrease in the amount of volume it can pump. You can compensate for the reduced volume by increasing the rate at which you pump. If you have a smaller heart you have to make it go faster. A mouse’s heart, for instance, can be pumping at two-four hundred times a minute whereas a big whale could have a heartbeat of say 20 or 10 times a minute but it has got a heart which is the same size as a Volkswagen beetle. That’s why.

On a related note, if you’ve got a very big heart it’s going to be almost impossible to empty that very, very quickly. It’ll be impossible to empty a whale’s heart which is several feet across 400 times per second. You just couldn’t shift the blood quick enough.  It's likely that the dynamics of muscle contraction wouldn’t be able to occur fast enough to make the muscle get shorter quickly enough en masse to move that amount of blood at that speed. It is a phenomenal thing to have achieved.

We put this question to Dr John Wood:

Well, I don’t know the particular circumstances. It’s possible, I hope, that maybe he had a vaccine but maybe not. He could have been exposed to flu in the past which gave him some immunity. Maybe he didn’t know he’d been exposed to flu in the past. It may have been a kind of sub-clinical infection he didn’t notice. I expect he had some kind of immunity.

We put this question to Cambridge University Researcher Ed Hutchinson:

In the case of flu you’ve got the fact that flu will spread from organism to organism so although we’re worried particularly about a human virus or a virus of livestock as well it actually starts of as a virus in waterfowl. Things like ducks where it’s not really a pathogen at all. It just lives in there and gets along with them. That doesn’t really tell you where a virus has come from. We know that they can spread from organism to organism. In the first place viruses probably evolve as just bits of the genetic sequence which just get out of hand and start copying themselves, moving to places they shouldn’t and acquiring more and more abilities along the way. There are quite a few examples of this where thing start jumping around inside genomes eventually will get the ability to jump from cell to cell as well.

Chris: In the answer to what came first, chicken or the egg, the virus cell situation has to be the cell came first, the virus came later.

Ed: Remember, the defining feature of the virus is that it’s absolutely dependent on taking over a cell to work. Without a cell the virus isn’t going to do anything at all.

We put this question to Cambridge University researcher Ed Hutchinson:

I’m afraid, unfortunately the answer is sometimes, yes you can.  Cold sores belong to a family of viruses called herpes viruses.  These don’t just include the famous sort of herpes we’ve all heard of but a whole range of viruses.  These viruses have a nasty trick of causing visible infection then hiding and coming back at various points in your life.  It’s called latency.  If the cold sore’s happening it’s hiding in some nerves in the side of your head and they’re coming back into you’re mouth on a regular basis.  Sometimes this is going to cause a visible cold sore and sometimes it’s going to cause something you can’t see but it’s still going to be shedding infectious virus into your saliva.  I’m afraid it’s always a risk.