The accidental scientist

  The price you pay for energy in $/kWh   Last week Pascale and I were invited to a barbecue on a very rainy and cool day. Our Kiwi friends didn ’ t cancel the party. Instead, the group gathered under the covered veranda around a small propane heater. What is the price of a kWh of energy in that form, I wondered? You can get an 8.5kg bottle of propane for $26.95, that is $3.17 per kilo. A kilo of propane yields 49 megajoules. A kWh equals 3.6 megajoules, so the price of a kWh is 3.6 x 3.17 / 49. That is $0.233. If you look at your power bill, it is shoulder time between 7am to midday, so you may pay about $0.249 per kWh. That is close, just a bit more than propane. What about the humble water kettle? You may wonder which type is cheapest to run. Gas or electric? At a glance, it looks about the same at shoulder time, when you make your morning tea. But we need to consider the device efficiency. The electric kettle efficiency is about 95%. Meaning 95% of the energy actually gets into

A couple of weeks ago my fire brigade attended a grass fire only 4 km from Piora. So we got there with our truck and circled it fairly quickly using air blowers. A big log kept burning somewhere in the middle and that was put off with water and foam, thanks to the help of the local farmer and his tractor who turned it over for us. A funny looking hole was found in the middle of that and one of my firies mates said this could well be caused by the lightning strike that started all this. Indeed electrostatic repulsion can move things, but is that enough to dig a hole? What causes lightning? It all starts with a strong temperature difference between two air masses within a cloud. The hot air goes up, the cold air down. The friction between the cold and hot air creates static electricity, so we end up with a positive charge at the top of the cloud and a negative charge at the bottom. When the voltage gets high enough, sparks form within the cloud, or between the base of the cloud and