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.