IGCSE Physics 0625

4.1 Simple phenomena of magnetism

Induced Magnetism

Induced magnetism is the process of creating a magnetic field in a material by moving a magnetic field near to it. This phenomenon is fundamental to the operation of many devices, including generators and transformers.

How it Works

When a magnetic field changes around a conductor (like a wire), a voltage is induced in the conductor. This induced voltage causes a current to flow in the conductor, which in turn creates its own magnetic field. This new magnetic field is called the induced magnetic field.

Factors Affecting Induced Magnetism

The strength of the induced magnetic field depends on several factors:

• Strength of the magnetic field: A stronger magnetic field will induce a stronger magnetic field in the conductor.
• Speed of the magnetic field: A faster-changing magnetic field will induce a stronger magnetic field in the conductor.
• Number of turns in the conductor: More turns in a coil of wire will result in a stronger induced magnetic field.
• Orientation of the conductor relative to the magnetic field: The angle between the conductor and the magnetic field affects the induced voltage and current.

Experiment: Demonstrating Induced Magnetism

A simple experiment to demonstrate induced magnetism can be carried out using a coil of wire, a magnet, and a galvanometer.

1. Connect the ends of the coil to a galvanometer.
2. Move a magnet quickly into and out of the coil.
3. Observe the galvanometer; a deflection indicates an induced current and therefore an induced magnetic field.

Mathematical Relationship

The magnitude of the induced electromotive force (EMF), denoted by ε, can be approximated by Faraday's Law of Induction:

$$ \varepsilon = -N \frac{d\Phi}{dt} $$

Where:

• ε is the induced EMF (in volts).
• N is the number of turns in the coil.
• Φ is the magnetic flux (in Weber).
• t is the time interval (in seconds).
• The negative sign indicates Lenz's Law, which states that the direction of the induced current is such that it opposes the change in magnetic flux that produced it.

Applications of Induced Magnetism

Induced magnetism is crucial for the operation of various devices:

• Generators: Generators convert mechanical energy into electrical energy by using the principle of induced magnetism. A coil of wire is rotated within a magnetic field, causing a change in magnetic flux and inducing an EMF.
• Transformers: Transformers use induced magnetism to step up or step down AC voltages. A changing current in the primary coil creates a changing magnetic field, which induces a voltage in the secondary coil.

Table Summary

Factor	Effect on Induced Magnetism
Strength of Magnetic Field	Stronger induced magnetic field
Speed of Magnetic Field	Stronger induced magnetic field
Number of Turns	Stronger induced magnetic field
Orientation of Conductor	Maximum induced magnetic field when perpendicular