Magnetic effects of electric currents – IB Physics Standard Level Revision

Introduction to Magnetic Effects of Electric Currents

The magnetic effect of electric currents refers to the phenomenon where an electric current flowing through a conductor creates a magnetic field around it.
André-Marie Ampère, a French physicist, was the first to demonstrate this effect, hence a unit of electric current named “ampere” after him.

Ampère’s Circuital Law states that the magnetic field in space around an electric current is proportional to the electric current which serves as its source.
Times the length of that path, is equal to the 1/µ₀ times the algebraic sum of electric currents through that path.
It is formulated as ∮ B.dl = µ₀I where µ₀ is the permeability of free space, B is the magnetic field, I is the electric current, and ∮ B.dl is the line integral of B over the closed loop C.

When current moves through a straight conductor, a concentric circular magnetic field forms around it.
The field is stronger near the conductor and weakens with the distance from the conductor.
The direction of the magnetic field can be determined using the right-hand grip rule. Imagine gripping the conductor with your right hand with the thumb pointing in the direction of the current. The direction your fingers wrap around the conductor is the direction of the magnetic field.

A loop or coil of wire, often wrapped around a magnetic core, is referred to as a solenoid.
When an electric current passes through a solenoid, it produces a magnetic field similar to that of a bar magnet with a distinct North and South pole.
The strength of this magnetic field can be increased by increasing the current, adding more loops to the coil and using a magnetic material as the core.

The magnetic effect of electric current is utilised in a number of devices including electric motors, and electromagnetic relays.
In electric motors, an electric current flowing through the rotor creates a magnetic field that interacts with another field (from a stator), causing the rotor to turn.
In electromagnetic relays, a small electric current flowing through one circuit causes a larger current to flow through another circuit, thanks to the magnetic field it creates.

Continuous exposure to strong magnetic fields can cause health problems such as headaches, dizziness, nausea, and impaired vision.
Therefore, it’s important to limit exposure, especially near high-voltage power lines, transformers, and large electric motors. Certain safety guidelines and regulations are in place for working with or near strong magnetic fields.