An odd effect on my camera

 I was trying to take a photograph of a sample of rock when I noticed this striped effect on my camera screen. It wasn't visible to the eye.

 My lamp looks like this:

I wondered whether it was an interference effect like Lloyd's mirror but the angles were all wrong. But it occurred to me that it might be that I was detecting the ac flicker of a fluorescent tube. Alternating current would mean it would be flashing 50 times a second. So why does that show up as line on the screen? To understand my theory, look at this photograph that I took from the coach on the Berlin trip

The odd angle on the back of the lorry suggests to me that the CCD on the back of the camera loads in lines from top to bottom. Hence the lorry has moved forward by the time the bottom of the picture is taken. If that's the case, then during an exposure, the light would be on for some lines and off for other lines, giving me my picture. 6 lines would give an exposure time of 0.12 seconds. However, the lines stay horizontal when I turn the camera through 90 degrees. Would the camera read the lines the other way if I turned the camera? Probably not so more thought necessary.

Acid and alkali - making salt

We made salt by mixing two clear and colourless liquids: hydrochloric acid and sodium hydroxide. Sodium hydroxide is an alkali. We started by placing a small volume of alkali in a test tube and added Universal Indicator, which went purple showing pH11. We counted drops of acid until the Universal Indicator went green. It was a neutralisation reaction. We had made an aqueous solution of sodium chloride. To get the crystals, we needed to evaporate away the water. The problem was that the salt would have the colour of the Universal Indicator, so we needed to repeat the experiment without the indicator. Here's the end product.

The experiment works because of the reactivity of the ions in the solutions. Sodium hydroxide contains Na+ and OH- ions. Hydrochloric acid contains H+ and Cl- ions. Na+ is more reactive than H+ because it finds it easier to lose electrons. It bonds more easily to the Cl- ion because that is the smallest of the two negative ions. The result is a cubic crystal lattice like this:

This lattice is a strong shape and that makes the molecule very stable. Stable means lower potential energy. In the same way that water flows to the place of lowest potential energy, so chemical reactions happen most often when they head towards lower potential energy. That's why this neutralisation reaction is able to occur and it is why acid and alkali make salt. Finally, notice that if the Na+ bonds with the Cl-, that leave behind H+ and OH-. Of course, that's H2O!!

Queen of the South and the cost of running floodlights

I took this picture at the Queen of the South ground in Dumfries. I was interested in how much it might cost to run the floodlights for a game. So:
1. Count the number of lights on the pylon in this corner of the ground.
2. Estimate the total number of floodlights in the ground.
3. If one light is 2kW, work out the total number of kW for the whole ground.
4. State how many hours you think the lights will be on for an evening game, giving your reasons.
5. Then calculate the total kilowatthours - the total kW x the hours.
6. If 1kWh costs 10p, how much will the floodlights cost for one game?

Haweswater: a novel and some volumes

I have posted about Haweswater several times in the last few months so I was interested to find this novel in the school library, by a Cumbrian author. It is set in the old hamlet of Mardale, which didn't quite emerge from the water this year, at the time Manchester Corporation were deciding to start building the reservoir. On page 50, it is suggested that the volume of the new reservoir will be twenty thousand million gallons. Now there are 0.004546 cubic metres in 1 gallon, which means the figure in the book equates to 90,920,000 cubic metres. Wikipedia gives a volume of 76,600,000 cubic metres http://en.wikipedia.org/wiki/Haweswater_Reservoir so the current stated volume may be less than originally envisaged. It also states that the volume is the same as 62,100 acre.ft. What a wonderful unit! An acre is about half a football pitch so it is a very wide and not very deep volume. In August I estimated that the reservoir was down by about 6 million cubic metres. That's not far off 10% of the stated volume so perhaps not a bad estimate http://www.wigtonphysics.blogspot.co.uk/2014/07/will-mardale-appear-from-haweswater.html Finally Wikipedia has introduced me to a concept called "residence time": the length of time it takes a water molecule to pass through the reservoir. This is 500 days. Nearly teo years...

Have a go at Super Planet Crash

There are very frequent announcements of the discovery of exoplanets. These are planets that go round stars other than the Sun. You can't see them with telescopes. They are so far away and the light reflected from them is so dull. Instead they are detected by picking up the small dimming effect when they pass across the face of their star, or by the way they make the star slightly wobble as they orbit. Both of these effects are greater if the planet is the size of Jupiter. Since we can't study systems like this directly by observation, computer modelling helps. Here's one such programme, made into a game: http://apod.nasa.gov/apod/ap150112.html Click the link and have a go at Super Planet Crash. My first few goes ended in catastrophe. I then played safe by installing 11 Earth sized planets and my system lasted 500 years. I got 115,766 points.

Then I tried again with a couple of ice giants and a giant planet thrown in as well. It was stable for 500 years and I managed 295, 400 points. Can you beat that? The game goes slowly so you might want to press fast forward when you are sure that it seems stable.

Take the physics teacher bowling

I hadn't been bowling for years so I'd like to blame overthinking it for my defeat. The balls have different masses. So should I choose a lighter ball that I can bowl faster or a heavier one that I find harder to shift? Would there be much difference in their momenta? In the end, I found that the faster I tried to bowl them, the less accurate. But I was struggling to get "strike" even with a heavy, slower, accurate ball. I could knock over 8 or 9 but not the elusive last couple. At the far end, is it momentum or kinetic energy that is important. If it is KE, then perhaps speed is more important because that squares. But I had less success with the lighter balls. Also, I get tired so it ceases to be a controlled experiment, More research needed.

Spark counter

The spark counter is a series of thin wires a few millimetres above the surface of a silver metal disc. The potential difference is adjusted to a few thousand Volts. The electric field strength in the gap between the wires and the plate becomes so big that it forces the air to conduct and you get sparks. You get this to happen and then turn it down slightly so that it is almost bu not quite sparking. Then you bring in the alpha radioactive source, as shown in the picture. The sparks come back. But you get nothing with beta and gamma. This is because the alpha particles are able to ionise air molecules, allowing the air to conduct and producing sparks. Putting paper in the way stops it.