Describing the world with fields may seem unfamiliar, but it is essential for fully understanding the universe and its forces.

• Quantum field theory(QFT) describes everything in terms of  fields:  particles are not independent objects but rather excitations of their respective  fields. Interactions between particles are actually  interactions between their fields.
• Similarly, space-time can be thought of as a field in general relativity. Although we may never  fully visualize the gravitational field, we use it in equations to describe motions and forces.

Now, let‘s explore two important fields: the electric field and magnetic field

You probably encountered them in various forms:

• The earth’s magnetic field shields us from solar radiation
• Electromagnetic fields enable communication in devices like smartphones
• Electric fields exist in capacitors and other electrical components

At its core, a field is a concept that assigns value – such as a force, vector, or magnitude- to every point in space.

Field lines

Field lines are a useful way to represent fields graphically. They follow these rules:

• Electric field lines originate from positive charges and terminate at negative charges.
• Magnetic field lines extend from the North to South Pole of a magnet but always form closed loops since isolated magnetic charges – monopoles do not exist.
• The strength of the field is represented by the density of field lines – closely spaced lines indicate a stronger field.
• Field lines never cross. Why not? If they did, a charged particle placed at the crossing of lines would have two possible directions of movement, violating the superposition principle (two different field vectors at one point always add up and combine to a single vector)

Another important concept is the equipotential line, which represents points in a field where a particle has constant potential energy.

Electric field

The electric field (E) is a vector field, meaning  it has both direction and  magnitude. It describes how the electric force (Coloumb force) acts on a stationary charge at any point in space.

In other words, the electric field tells us  how the electric force is transmitted through space and how a charge influences the surrounding space.

The relationship between force and electric field is given by:

E=F/q

Where E is the electric field strength, Fi is the force acting on a charge, and q is the charge.

This equation shows that a charge q placed in an electric field will experience a force F in direction of E if q is positive or in opposite direction if q is negative.

Magnetic field

The magnetic field (B) is also a vector field, it has both direction and  magnitude. It describes how the magnetic force is transmitted through spaces and how it affects moving charges.

What exactly is a magnet?

Elementary particles, such as electrons, have a quantum property called spin – we can imagine it as a rotation of the particle around its own axis. This spinning particle creates a tiny magnetic field.

Thus, elementary particles behave like tiny magnets. When many of these particle magnets align in a material, they create a permanent magnet.

The force on a moving charge in a magnetic field is given my the Lorentz force equation:

F=q x (v x B)

Where F is the magnetic force, q is the charge, and v is the velocity of the charge.

Differences electric and magnetic field

• he electric field exists around both moving and stationary charges
• The magnetic only exists around moving charges

• Electric monopoles do exist (e.g. a single positive charge)
• Magnetic monopoles do not exist – a North Pole always has a South Pole

• Electric field lines extend infinitely unless terminated by an opposite charge
• Magnetic field lines always form closed loops

• The unit of the electric field is volts per meter (V/m)
• The unit of the magnetic field is Volt-seconds per meters squared (Vs/m^2) or Tesla

• An electric field does work on a charged particle, changing its kinetic energy
•  A magnetic field does no work on a charged particle, it only changes its direction

The electromagnetic field

A moving charge creates both a magnetic and electric field. The fields are inseparable - one generated the other, forming the electromagnetic field.

 The idea  was formalized in Maxwell‘s equations, which summarize the behavior of electric and magnetic fields:

1. Electric charges create electric fields
2. Magnetic monopole can not exist – magnetic field lines always form loops
3. A changing magnetic field induces and electric field – the principle behind electric generators
4. A changing electric field induces a magnetic field which explains how electromagnetic waves propagate

The last two equations explain how light and other electromagnetic waves travel through space. A changing electric field generates a magnetic field, which in turn generates another electric field, and so on – allowing energy to move forward without a medium.

This is why light can travel through empty space, unlike sound waves, which need a medium such as air to propagate.