# Concept, History, Formulas, and Examples of Magnetic Field Problems

Examples of Magnetic Field Problems – In everyday life, we need magnets. With magnets some elements of life become easier. In the Big Indonesian Dictionary (KBBI) magnet is defined as any material that can attract ferrous metal; excitability.

Magnets have a magnetic field whose functions can be used for daily needs. The following is an explanation of the magnetic field which has been summarized from various sources on the internet.

## Magnetic Field Concept

Launching from the Id.wikipedia.org page, a magnetic field is a field formed by moving electric charges (electric currents) which causes a force to appear on other moving electric charges. Simply put, the magnetic field is the space or area around the magnet that is still affected by the magnetic force.

The magnetic field can be permanent from a ferromagnet because there is a quantum mechanical spin from one particle forming a magnetic field and the spin is influenced by itself. This event is known as an electric current.

A magnetic field is the same as a vector field, that is, it is related to each point in a vector which can change according to time. Meanwhile, the direction of this field is balanced or equal to the clockwise direction of the compass placed in the magnetic field.

The magnetic field is a force field that lies around magnetic objects or around current-carrying objects. The magnetic field is usually represented by arrows and represented by lines. The magnetic field is described by lines of magnetic force that always come out of the north magnetic pole and enter the south magnetic pole.

Meanwhile, inside a magnet, the lines of magnetic force are directed from the south pole to the north magnetic pole. These lines never intersect. The strength of the magnetic field can be seen from the density of the magnetic lines of force. Launching from the Sumber.belajar.kemdikbud.go.id page, the following are important things to pay attention to regarding magnetic lines of energy.

• Magnetic lines of force never intersect.
• Magnetic lines of force always leave the north magnetic pole and enter the south magnetic pole.
• A place where the magnetic lines of force are close together indicates a strong magnetic field, whereas a place where the magnetic lines are far apart indicates a weak magnetic field.

When two magnets with different poles are brought closer, a large magnetic field will arise. However, when two magnets that have the same poles are brought closer, there will be no magnetic force lines that form a magnetic field.

In Einstein’s opinion, there is special relativity which shows that electric fields and magnetic fields are two aspects of the same thing (2nd degree tensor). And only an observer who is able to feel the magnetic force in which a moving observer only feels electrostatic charges. Therefore, using special relativity, the magnetic force can be defined as the manifestation of the electrostatic force of moving electric charges.

The earth itself has a magnetic field which is called a geomagnetic field. Earth is a bar magnet that has two poles, a north pole and a south pole. Earth’s magnetic field occurs because of the outer core of the fluid with a dynamo process. Meanwhile, the source of the magnetic field on earth is located in the earth’s core, the earth’s crust, and parts of the ionosphere and magnetosphere.

## History of the Magnetic Field

Launching from the Zenius.net page, the concept of a magnetic field was known by ancient peoples. However, research on the magnetic field was only started by Petrus Peregrinus de Maricourt in 1269. He did this by mapping the magnetic field using a magnetic ball and an iron needle.

From this experiment, it emerged that the magnetic field lines crossed at two different points. To simplify his research, Petrus gave the names of the two points “poles” because they were inspired by the poles of the earth. Magnets always have two different poles. Therefore, even though it is cut many times, the magnet still has two different poles.

Three centuries after Petrus Peregrinus put forward his theory of the magnetic field. William Gilbert replicated his research by publishing De Magnete in 1600. This work eventually helped establish magnetism as a science (enter into science ).

In 1831, Michael Faraday discovered the existence of electromagnetic induction. Electromagnetic induction explains that a circular electric field can be generated from a changing magnetic field. This discovery is still used today under the name of Faraday’s law of induction.

Meanwhile, another formula that discusses electricity and magnetism was discovered by James Clerk Maxwell. He published the equation of these two things in his research entitled On Physical Lines of Force in 1861. Although it can be proven and declared valid, this equation seems incomplete.

Later, Maxwell completed his equation formula in another research entitled A Dynamical Theory of Electromagnetic Field in 1865. In that research, Maxwell was bolder in stating that light is actually an electromagnetic wave. In 1887-1888, Heinrich Hertz proved Maxwell’s discoveries and verified their correctness.

The development of the modern magnetic field was again proven by the discovery of Nikola Tesla in 1887. He succeeded in developing an induction motor that runs on polyphase currents. It should be noted that polyphase currents are two (or more) alternating currents that have the same frequency but different phases. This current will produce a rotating magnetic field to drive the motor. From his invention, Tesla obtained an electric motor patent in 1888.

Entering the 20th century, the discussion of magnetic fields has expanded to special relativity, classical electrodynamics, and quantum mechanics. One of the well-known scientists, Albert Einstein also explained that magnetic fields and electric fields are a similar concept, but the discussion uses a different way and frame of mind.

## Application of Magnetic Fields in Everyday Life

Actually in everyday life, we have come into contact with magnetic fields. Just didn’t realize it. The following is the application of magnetic fields in everyday life, as quoted from the Zenius.net page.

### 1. Electromagnets

The application of a magnetic field using electromagnetic. For example on the doorbell. The working principle is quite simple, when pressing the buzzer button the electromagnetic will move the striker to make the bell ring.

Another example is loudspeakers. When singing, speaking, or making any sound with a device connected to the speaker via Bluetooth. Then the electromagnetic will receive the rhythm and the conductor (usually a cone attached to the electromagnetic, controlled by an electric current) will receive the rhythm and output it back at the loudspeaker.

### 2. Magnetic Levitation

Magnetic levitation or maglev is the application of a magnetic field to electric trains. Thus, the train can run at high speed. This is also implemented by electric trains in Japan, namely the Shinkansen.

When a train is able to ride right on the rails, very little friction occurs in a magnetic field, making it easier to move the train and make it move quickly.

### 3. Motors

The motorbike in question is not the motorbike that we usually see on the streets. The motor here is defined as a machine capable of converting energy into motion. Meanwhile, the application of a magnetic field in everyday life is the use of a magnetic field to be able to rotate the axis.

Therefore, the electric current flowing to the motor varies. They will work together to form a magnetic field that goes up and down so that it will push the motor core around it. For example cars, computers, elevator doors, and so on.

## Magnetic Field Formula

Here’s the magnetic field formula.

`B = μI / 2πr`

Information

B = magnitude of the magnetic field (T)

μ = permeability constant (4π 10-7 Tm/A)

I = electric current (A)

r = distance from the cable (m)

To find the amount of electric current, you can apply the formula below.

`I = B 2πr/ μ`

Information:

B = magnitude of the magnetic field (T)

μ = permeability constant (4π 10-7 Tm/A)

I = electric current (A)

r = distance from the cable (m)

## Example of a Magnetic Field Problem

The following are examples of magnetic field questions that have been summarized from various sources on the internet.

1. A wire has an electric current of 4 A and a distance of 2 m from the cable. Calculate the magnitude of the magnetic field!

I = 4 A

r = 2 m

So,

B = μ I / 2 π rA

B = 4 π 10-7 4 / 2 π 2

B = 4 10-7 T

So, the magnitude of the magnetic field is 4 10-7 T

2. A wire carries an electric current i = 4 A as shown below!

Define:

• Magnetic field strength at point A
• Magnetic field strength at point B
• The direction of the magnetic field at point A
• The direction of the magnetic field at point B

Is known

I = 4 A

rA = 2m

rB = 1m

Completion

B = μ0 I / 2 π rA

B = 4 π 10-7 4 / 2 π 2

B = 4 10-7 T

So the magnetic field at point A is 4 10-7 T

B = μ0 I / 2 π rB

B = 4 π 10-7 4 / 2 π 1

B = 8 10-7 T

So the magnetic field at point B is 8 10-7 T.

In questions that ask for direction, we can use the right-hand rule, where the thumb is assumed to be a current and the other four fingers are a magnetic field with the position of holding the wire at point A.

So that the direction of the magnetic field at point A is outward or approaching the reader.

In questions that ask for direction, we can use the right-hand rule, where the thumb is assumed to be a current and the other four fingers are a magnetic field with the position of holding the wire at point B.

So that the direction of the magnetic field at point B is inward or away from the reader.