Neurons in our bodies carry weak currents that produce detectable magnetic fields. A technique called magnetoencephalography, or
MEG, is used to study electrical activity in the brain using this concept. This technique is capable of detecting magnetic fields as weak as 1.0 10-15 T. Model the neuron as a long wire carrying a current and find the current it must carry to produce a field of this magnitude at a distance of 3.6 cm from the neuron.
Warmer air is less dense than cold, which is why warm air tends to rise and cold air sinks. Being acted on by gravity, colder, denser air weighs more and exerts greater pressure per unit area.