About this blog

Physics can be difficult to learn, but this blog aims to help you get into physics by connecting your GCSE physics lessons with things you see in the world around you.

Friday, 17 June 2011

Black is the New White

This is an appeal. Please, please convince everyone you know to paint their radiators. Not another coat of nice shiny white gloss, but a nice black. Tell them it will save them money, tell them it will help protect the environment, ask them to get you to explain it to them so that they too will see that black in the best colour for them to be.

You see, it all comes down to heat transfer. Heat is transferred by a variety of methods, the main ones being conduction, convection and radiation. The clue is in the name here, and radiators give out their heat by (you’ve guessed it) radiation, although the room is actually warmed by convection of the air currents. This type of heat emission depends heavily on what the properties of the surface are.

Dark surfaces are much better emitters of radiation than light surfaces, because they absorb and emit infra-red rays much more readily. These rays are the way that heat is carried when we’re talking about radiation. When you see a photo showing hot and cold areas, this is taken with an infra-red camera. A simple experiment to check I’m not just making this up would be to leave a black and a white top out in the sun for an hour and when you come back to touch them, the black one should be much hotter.

So we know that our radiator should be black, but can it still be shiny? The answer is no if you want the full effect, because matt surfaces are better emitters than shiny ones. This is because the shiny surfaces reflect too much radiation rather than letting it pass through into the atmosphere (your room). So a matt black radiator it is then!

Is there any use for shiny and light coloured things? Actually, if you want to get really eco-friendly about it, you can use tin foil on the wall behind your radiator to reflect the heat back into the room, which will add yet further efficiency. You might even find yourself in a great bargaining position to get that new console if you save enough money.

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