If a tree falls in the forest...

We found this tree rocking backwards in the forest above Loch Rannoch. It reminded me of the old question: "If a tree falls in the forest and there is no one there, does it make a sound?" This gets to the heart of the definition of sound. Yes the falling tree will make the particles in the air vibrate, But by sound, we surely mean that those vibrations are detected and interpreted. That needs some higher life form. We were there and we observed. If it's fallen since our visit, then it didn't make a sound!

Basic principles of radar

I was teaching about ultrasound the other day. Radar works on a similar principle that a pulse is sent out and that some of it is reflected back. If you look at the trace in the picture, the amplitude of each reflected pulse is much smaller. In the same way as with an ultrasound scan, you use the oscilloscope trace to calculate the time it takes for the pulse to go out and to reflect back. Use distance = speed x time for your calculation. In this case it's an electromagnetic wave so it's the speed of light you need. The distance to the aeroplane is half your calculated distance because the pulse has gone out and back.

GCSE revision: why I think transformers are odd!

I remember once showing this to a class and they were underwhelmed. They said "we press switches every day and lights come on, sir". But what makes me think it is odd is that both coil A and coil B have insulated wires. Even though the core around which they are both wrapped is of iron, there is no way the current can get out of one wire and flow through to the other wire. Coil A is an electromagnet. The squiggly line is an a.c. power supply. That means that the poles of the electromagnet keep changing direction. This changing magnetic flux then waggles backwards and forwards in coil B because the flux can travel to coil B through the iron. As pointed out yesterday, waggling a magnet inside a coil produces induced electricity - that's what causes the bulb to light. We also showed that coils with fewer turns had a smaller induced voltage. That's how a step down transformer works.

GCSE Revision: Electromagnetic induction

We showed that if we moved the magnet up and down inside the coil, we got a reading on the voltmeter. In this case, south pole into the hole went positive and south pole out went negative. In other words, changing direction of movement makes the voltage flip from positive to negative so we have made AC electricity. It also works if you hold the magnet still but move the coil up and down.

You get the same thing if you move a copper wire up and down between the poles of a powerful horseshoe magnet. We say that there are invisible flux lines going from the north pole to the south pole which make up the magnetic field (it is possible to use iron filings to show them). The copper wire was chosen because it is not a magnetic metal. It cuts down through the flux lines like a cheese wire through cheese. As long as it is MOVING you get a voltage induced. Downwards made a negative voltage and upwards made a positive voltage.

Finally I waved the powerful magnet near the coil. It didn't even have to go into the coil to get an induced voltage. As it moved, the flux lines coming out from it cut through the coil. All of the methods shown are called ELECTROMAGNETIC INDUCTION. They are used in generators and make AC electricity.
The non-essential part is to say that they work by getting the magnetic field to drag electrons along inside the wire. Moving electrons = electric current.

A strange mapping

I have been experimenting with the panorama function on my camera. I have to spin gently holding the camera whilst it tales photograph after photograph and stitches them together in one big picture. So it is taking a curved 3D world and mapping it onto a straight 2D space. It must be related to those maps of the world where the globe has been cut like orange peel and squashed flat onto the page. Things get stretched and warped. Just so with this picture. Look at how the straight railway line in the bottom right of the picture has been pulled into a curve. This is similar to stuff I was reading in Roger Penrose's book The Road to Reality. He is dealing with how we cope with curved space-time in at least 4D.

Ground source heat pump at Croome

The idea is that they are going to bury a lot of pipes under the field in front of the house. In the winter it is warmer underground than above ground. There is a mixture of water and anti-freeze in the pipes. Thermal energy can get the from the ground into the liquid by travelling along the temperature gradient due to the temperature difference. The thermal energy is then taken up to the house. Sounds unbelievable but it works.

Pudding stone conglomerate on Conic Hill

An amazing feature on Conic Hill was the conglomerate rock. It had large rounded pebbles. It looked like concrete. They must have been transported a decent distance to have been rounded off like this. It was similar to the rock I found last summer on Rhossili Down. That was said to have come from a river delta millions of years ago. The visibility was so good when we visited that Arran is visible in the far distance in the top picture. Today I was at St Bees and saw pebbles on that beach.

Perhaps if I come back in millions of years time this will have become pudding stone. It puts the nature of time into some sort of perspective!