what is the magnetic effect of placing two wires with equal but oppositely directed currents close together or twisted about each other?
This reduces the radiated magnetic field and the inductance of the pair of conductors. It also reduces the pickup of electronic noise in the pair of wires (providing a type of shielding).
The magnetic effect of placing two wires with equal but oppositely directed currents close together or twisted about each other is the creation of a magnetic field. This phenomenon is known as the Ampere's Law or the Biot-Savart Law.
To understand this effect, you can use the right-hand rule. Spread out your right hand and point your thumb in the direction of the first current. Then curl your fingers towards the second current. The direction your fingers indicate is the direction of the magnetic field created by the currents.
The magnetic field lines around the wires form concentric circles, with the wires being at the center. The magnetic field strength is directly proportional to the magnitude of the current flowing through the wires. Hence, when the currents in the wires are equal but opposite, the magnetic fields cancel out in the region between the wires, resulting in a weak overall magnetic field.
However, when the wires are twisted about each other (forming a helix or a coil), the magnetic fields generated by each wire add up, resulting in a stronger magnetic field inside the coil. This is the principle used in electromagnets, where a coil of wire carrying an electric current creates a strong magnetic field when the wire is wrapped around a ferromagnetic core.
In summary, placing two wires with equal but oppositely directed currents close together generates a weak overall magnetic field, while twisting them about each other increases the magnetic field strength, as seen in electromagnets.