Having recently posted a general piece about spin in general (https://physbang.com/2024/11/24/what-is-spin/) I thought it would be useful to discuss one particular use of spin in a practical context; cooling. Suppose we have a material with a single unpaired electron in each of its atoms. The lone electrons can either be spin-up or spin-down and on … Continue reading Spin Cooling
Key Facts: Waves
We can define a wave as something that carries energy from one place to another without the transfer of physical matter. To understand this definition it is useful to think about two different ways of feeling heat. In a shower, heat is created by an energy exchange inside the storage tank or shower unit and … Continue reading Key Facts: Waves
Specific Heat Capacity
Heating a substance can cause either an increase in temperature or a change of state. This is not completely obvious, so let me put it another way; sometimes when we "heat up" a substance it doesn't actually get any hotter. The reason for this is that the energy supplied is being used to break bonds … Continue reading Specific Heat Capacity
Surface Colour and Cooling
In the same way that surface colour affects the rate at which objects heat-up and the maximum temperature that they reach (as discussed here) so too will the surface colour affect the rate of cooling. As before, there is a standard experiment that you are expected to know and a typical set of curves that … Continue reading Surface Colour and Cooling
Surface Colour and Heating
Most people say you shouldn't go out on a summer's day wearing black because you will get too hot. It would be much better to wear white as this will keep you cooler. But is that actually true? We can test this idea using two boiling tubes that have been sprayed to have different surface … Continue reading Surface Colour and Heating
Thermal Equilibrium
Any object that has a constant temperature is in a state of thermal equilibrium. This means the rate at which energy is transferred to the object is exactly equal to the rate at which energy is transferred from the object. In the context of electromagnetic radiation, we can state that the rate at which the … Continue reading Thermal Equilibrium
Light and Heat
It is obvious to say that hot objects emit (give off) both visible light (a glow) and heat (that we can feel but not actually see). This is true of bonfires, light-bulbs and even our Sun. The connection between heat and light is taken completely for granted in everyday life: the glow of a hot … Continue reading Light and Heat
Energy Stores and Transfers
Energy is the property of a system that enables it to do work. This is often stated bluntly as; “energy makes thing work”. There is a fundamental law in physics, which states that the total amount of energy in a system always remains constant. Energy cannot be created and it cannot be destroyed. Energy can, … Continue reading Energy Stores and Transfers
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