# Tag Info

4

When you touch something, you don't feel how hot/cold the thing is; you feel how hot/cold it makes your hand. Metal conducts heat more easily than wood. So if wood and metal are hot, the heat will flow more easily from the metal to your hand. If wood and metal are cold, the heat will flow more easily from your hand to the metal.

1

Convection requires the hot air just above your soup that has been heated up to rise as its density reduces after being heated, allowing the colder air around the rising hotter air to replace the hotter air and the same thing will happen again. As the convection currents (the rising of the hot air and the sinking of the cold air) keep taking place just above ...

1

The equation: $$dS = \frac{dQ}{T}$$ only applies to reversible processes. For an irreversible process $dS \gt dQ/T$. To see this start with the expression for the change in internal energy: $$dU = dQ - dW$$ The internal energy is a state function, so this equation always applies whether the process is reversible or irreversible. So for a reversible ...

1

The sign is governed by the convention - whether the volume is of your system in consideration or not. If you decrease the volume of your system - you increase the energy of your system, so you require for total energy change to be positive. If the volume is describing your system then $dV <0$ and so $dE=-PdV>0$ is the correct expression If the ...

1

In some high-demand medical facilities, liquid oxygen at cryogenic temperatures (in tanks) is used (http://208.76.246.34/~ava/Oxygen-source.pdf). More often, gaseous oxygen in metal cylinders is used. The pressure may vary, but the above source gives 13700kPa (for UK).

1

The answer depends on the nature of the "huge oxygen bottles"... You often see large ( around two stories high) tanks outside a hospital. They are distinguished by the name of the chemical firm, Union Carbide or Linde among others, painted on the side, and by the thick layer of frost found on the attached plumbing. These tanks hold liquid oxygen at low ...

Only top voted, non community-wiki answers of a minimum length are eligible