Projecting onto an oblique curved surface

I went to see the brilliant Katherine Priddy play in a tent. The blue spotlights were circular so the beam must have started circular. It hit the tent canvas in the middle top of the photo, spreading out into an almost parabolic shape. A very clear visual mapping from a circle to a parabola. 

Vapour trail

There is a whisp of vapour trail in the middle of the picture. I watched the plane pass. It seemed to go through the high cirrus cloud. Why did the contrail persist there and not elsewhere? Is it that the humidity is high there so it can't evaporate? Is that why there is a cloud there in the first place?

Tare

 I have been aware of the TARE button on electronic balances for several decades but thanks to Mrs B for pointing out the definition in an old dictionary from over a century ago, as being the mass with the container removed. In recent years, it has often been labelled as the "zero" button. Place the container on the balance and press it to make the reading set to zero. It's interesting that it had a usage similar to algorithm. And its other usage: I thought tares were generic weeds but it seems to be specifically Vetch.

Slight aurora

I was out at 9.30pm on an Amber alert and was able to photograph a faint aurora. I was not able to see anything directly with my eye.

Below is another 9.30pm image

At 1.30am after a Red alert, even the camera was struggling to pick up the aurora. The effect is very variable.

Heavy electric cars

This is because electric cars are so much heavier due to the batteries. Can be a bit of a nightmare at festivals if it gets muddy.

The Perseids

Last night the conditions were perfect. A beautiful clear sky. Sadly I missed any trace of the aurora but in my half hour out I did see two meteors. I had a lovely view of Perseus. I have learnt a new word: radiant. I have enjoyed reading about comet Swift-Tuttle. It is interesting that after its discovery in 1862 that they predicted incorrectly the date of return. With something that has a 133 year orbit, it is hard to figure out on one viewing how long its orbital period is because you have to wait so long. It turns out it had been seen before so that made it predictable. And the dust that it left behind perhaps 1000 years ago gives us our annual spectacle.

How long does a solar panel last?

It finally occurred to me to ask what the lifespan of a solar panel is. I found this information from the States. They are suggesting maybe 25 years. It suggests that they will go past the break-even point but it is not as long as I'd expect a roof to last.

 

Fluorescent watch

Sunlight provides enough energy to move electrons up energy levels. As they de-excite and fall back they release visible photons. A question arises about the time delay. How have they been able to stay excited long enough to de-excite when I go into the dark later?

Back of the fridge

The fridge acts as a heat pump. Thermal energy from the objects inside the fridge is transferred to a fluid and then transferred from the fluid onto the black grill. Now I'm not teaching I can say that it passes by conduction into the metal grill. From there, the thermal energy is transferred to the surroundings. This can be by conduction to air particles, which gives them more kinetic energy making them spread out. The result is lower density air that floats upwards. But there is also heat radiation, the emission of infra-red radiation. This is why the grill is painted black as this is the best emitter colour. The large surface area works well for both methods of heat transfer into the surroundings.

Voltmeters

Unlike an ammeter, a voltmeter must have a very high resistance. In theory, no current should flow through it. If current flows, then a potential difference is set up across the voltmeter. If the voltmeter were connected in series, it would take the lion's share of the available emf in a loop, according to Kirchoff's Laws so voltmeters are in parallel. Even then, unless the voltmeter's resistance is very high it will reduce the current flowing through the component being measured and thus lower the measured potential difference.

 

Haltwhistle as the Centre of Britain

 

I have posted before about Dunsop Bridge's claims. That is done by the centre of gravity of a 2D shape method. Haltwhistle seems to be the the method of measuring the half way point between as many coasts as possible. See here for details. 

Where have all the rainbows gone?

It's been a very showery summer in Wigton yet this morning's rainbow is the first I've seen for a few months. The reason is to do with why the rainbow is such a low arc. Rainbows are centred around the extra-solar point, which is an imaginary point as far below the ground as the sun is above it. The rainbow is part of a circle around that point. When the sun is very high in the sky in the summer, the extra-solar point is very deep so only a small fraction of the circle is visible. This was what was visible early morning in August. For the past couple of months, so little will have been visible and that explains why I haven't been seeing them.

Ammeter

I loved the circuit symbols in the windows of the Electronics Department at the University of York. Because an ammeter measures the flow of current, it must be in series so that it experiences that flow. So as not to interrupt the flow, it must have vanishingly low resistance. If one were placed in parallel to a component, current would flow through it rather than through the component, thus rendering the component useless. In other words, it would act as a short circuit.

 

An interesting approximation

I was intrigued that the sign said "Scandinavia 401 miles (approx). I think it's a clever joke but suppose we took it seriously. Now approximating must mean some decision to round. Here the rounding has been to 3sf and that might be appropriate if the actual distance is measure to the nearest yard or inch. It would work if you are measuring to a point. The problem is that Scandinavia is quite an amorphous concept. Where would we place the point to mark Scandinavia? 

Squirty cream

Lovely feature in the Guardian by Mark Miodownik about nitrous oxide. It turns out it's in my squirty cream. Putting it under pressure increases the boiling point so it is a liquid at room temperature. It dissolves in fat. When the pressure is released it vaporises instantly spreading bubbles in the fat! 

Finding out about Plum Concrete

 

The notice board by the Elan Valley dams mentioned "concrete with plums". I'd not heard of that before. Turns out it is plain concrete with large rocks placed in it. When water is added to cement, an exothermic reaction takes place that releases a lot of thermal energy. The amount released in something the size of a dam would be huge. If maybe 40% of the mix is rocks, then this reduces the amount of thermal energy released.

Haltwhistle Viaduct like a parabolic reflector for sound

 Where Haltwhistle Viaduct crosses the Tyne there is a weir.

Approaching from the other side there was a roaring coming from above me that sounded like a strong wind. The sound of the water was being reflected and focused by the curved underside of the arch.

Avoirdupois again

This was in the museum at Llandrindod Wells. I've never seen the avoirdupois system made so prominent, perhaps to distinguish from other uses of LB. Interested to note that they made an international standardised version as late as 1959 so a pound is a pound in all countries.

Fence post machine

This machine is a wonder. It holds the posts in place and then hammers them in. The hammering action involves hoisting a metal cylinder and letting it fall. I am estimating the cylinder to be 50cm high with a diameter of 20cm. That gives a volume of about 15000 cm^2. If it is steel, the mass is 125 kg. If raised to 50cm above the post, it will hit it with a theoretical velocity from the v^2=u^2 + 2as equation, giving about 3m/s. Suppose it stops in 0.1 second on hitting the post. Force = change in momentum/time taken = 125 x 3 / 0.1 = 4kN to 1 sf. 
 

Lerwick Power Station

I always like researching the power supplies for islands. I spotted this at the far end of Stornoway harbour. You can read about it here. It is on the wonderfully named Battery Point - in the old usage of a gun battery! It seems that the power station is now used as a top up supply in the winter when the demand is higher than can be supplied from the mainland. I'm interested that there are plans for an HVDC cable to connect up the wind turbines to the mainland as well.

 

Metamorphic aureole at the other Wasdale

 

This picture shows a rock formation with the ruined Wasdale Farm near Shap. The hill behind is the site of the Shap Red Quarry, so is the location of the Shap Granite intrusion. Just a few hundred metres away, the rock is very different. The picture below shows layers, so I had come out into the metamorphic aureole where the heat had baked the existing country rock.

Polarisation reverses the colours

 

My polarising sunshades produced a diffraction effect on the edge of this cup of water. Pinker colours at the bottom with yellow and green above. When I rotated the polariser through 90 degrees, the order of the colours reversed.

Strange sundog

 

This was a strange optical phenomenon. Very high thin cloud produced a sundog - the small rainbow effect that appears either side of the Sun. However a lower layer of cloud was obscuring the Sun so there was no apparent cause for the tiny rainbow!

Looking for the guilty sunspots

After the aurora, I went looking for the cause. It's this cluster of sunspots.

I drew them on with a pencil. The sun quickly moved position! The screenshot below came from here.

It is 3664 that caused the damage. This is a region, not one sunspot. It is the regions that get the serial numbers. A lot more to unpack here.

Evaporation by proxy

When I put my cup on the table, there was early condensation on the surface. I poured hot coffee into the metal enamel mug.

Lifting it after 10 minutes, there was still condensation underneath.

15 minutes later, the table had dried where the cup had been. The thermal energy from the coffee conducted into the metal walls of the cup and thence into the condensation. The warmer condensation wanted to evaporate but couldn't because there was no contact with the air underneath the cup. When the cup was removed, the condensation evaporated using thermal energy that actually came from the coffee above it.

No second helping of aurora

I tried again twice on Saturday night. At 2am, it was a 200nT Red Alert on the app. Nothing doing. In the morning I found this article here. I was interested in the classification of a G4 geomagnetic storm. Turns out there are several ways of measuring the strength of a geomagnetic storm but the G scale is from the US. See here for info.

Aurora at last

This was the alert. 

This is what the camera saw. To our eyes, much less colour and looking like cirrus at weird angles. Also wasn't expecting it south of the house. 

Zero Error

I have been noticing that the altitude readings on my app is always about 50m too high. The viewpoint on Brock Barrow has a spot height of 223m so the screenshot below confirms that magnitude of zero error. 

Oscilloscope app

Turns out I have a sound oscilloscope app. Here's me whistling. 4 cycles in 3ms means T=0.75ms. Frequency = 1/0.00075 = 1300 Hz which sounds about right. 

Under the M6

I got under the M6 at Carnforth. Not surprisingly the thick concrete is a decent sound insulator. 

Porphyritic granite on the Pentland Road

Hello There's a cutting on the Pentland Road about 2 miles east of Carloway with an obvious vein of big crystal granite in it. Looks like it has intruded  between earlier layers. BGS viewer suggests a vein of Uig Hills - Harris Igneous Complex which could be around 2 billion years old.

The phenocrysts are very like those in Shap granite. 
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But it's quieter inside the car!

Sat inside the car it is 10dB quieter.