Final answer:
a. Assuming a typical 1 A current in an electric blanket wire, the magnetic field strength near a fetus, at a 1 cm distance, can be estimated using Ampère's Law.
b. Pairing wires with opposite currents in electric blankets reduces the external magnetic field through cancellation effects, minimizing potential health concerns.
Step-by-step explanation:
a. Estimating the magnetic field strength a fetus might experience involves several assumptions. Let's assume a typical electric blanket with a current of approximately 1 A and a wire separation of about 1 cm.
Using Ampère's Law, the formula for magnetic field strength (B) around a straight conductor is given by:
B = {μ_0 . I} / {2π . r}
where:
- B is the magnetic field strength,
- μ_0 is the permeability of free space (4π x 10^{-7}, T . m/A),
- I is the current in the wire,
- r is the distance from the wire.
Assuming a distance (r) of 0.01 m (1 cm), the magnetic field strength can be calculated.
Additionally, to compare with the Earth's magnetic field, the Earth's magnetic field strength is approximately 25 x 10^{-6}, T.
b. Pairing wires carrying current in opposite directions creates canceling magnetic fields around each wire, reducing the net external magnetic field.
This is due to the magnetic fields produced by the two wires interacting in opposite directions, resulting in a decreased overall magnetic field in the surrounding space.
This practice helps minimize the potential health concerns associated with external magnetic fields from electric blankets.