Question

Is your electric blanket safe? It has been theorized that excess nighttime exposure to electromagnetic fields may reduce the production of the hormone melatonin in certain women. Furthermore, reduced melatonin levels might lead to an increased risk of breast cancer. Scott Davis at Seattle's University of Washington School of Public Health and Community Medicine was one of the first to investigate links between electromagnetic fields and cancer (particularly leukemia). He has been quoted as saying, "Electric blankets were pretty effectively re-engineered a number of years ago. Modern-day electric blankets ? anything you buy in the store now ? (has a different) configuration of the heating elements in the blanket so that it doesn't produce any magnetic fields." How could the wiring in an electric blanket be designed to minimize or eliminate the production of external magnetic fields?

Answer 1

Well if we consider Bio-Savart law, we know that each element of current will produce a small magnetic field that depends on the distance from the wire that carries the current element; now this magnetic field has a direction that is opposed to the one produced by the same current but this time going in opposite direction. So we really need to somehow entangle the cables in order for them to be as close as possible but in a way that this entanglement of them involves two different directions for the currents and as well as same magnitudes; this way they will produce the same magnitude for the magnetic fields at one point but with opposite direction, which means the magnetic fields produced by both cables would cancel each other out at any point outside from the electric blanket. If we design the blanket this way, we will minimize the magnetic fields as they will be canceled due to the different direction of one current with respect to the other inside the entangle cables.