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Magnetic Flux Density Formula, Definition, Unit, Calculations

What is Magnetic Flux Density?

Definition: Magnetic flux density is the magnetic flux per unit area in a magnetic field. Additionally, Magnetic flux density refers to the amount of magnetic flux per unit area in a magnetic field. The Magnetic flux density formula is B = Φ / A.

It is a vector quantity, meaning it has both magnitude and direction. The unit of magnetic flux density is the tesla (T) in the International System of Units (SI). We use B as a symbol of magnetic flux density.

Magnetic Flux Density Unit

The magnetic flux density, measured in teslas (T), is a way we understand the strength of a magnetic field. It is like a “push” that magnets or electric currents create. The other units we use to measure magnetic flux density are wb/m2, Tesla(T), and gauss. Imagine you have a strong magnet. If you put a piece of metal close to it, the metal might feel a strong push, showing a high magnetic flux density.

However, if you use a weaker magnet, the push on the metal would be weaker, indicating a lower magnetic flux density. Teslas are the units we use to measure this push. One tesla is quite strong, like the pull of a strong magnet. If you have something that measures 0.5 teslas, it means the magnetic push is not as strong – like a weaker magnet. So, when we talk about magnetic flux density in teslas, we are talking about how strong a magnetic field is. It is a bit like measuring the “power” of the magnetic effect.

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Understanding Magnetic Flux and Magnetic Field

Before I explain what magnetic flux density is, let me briefly touch upon the concepts of magnetic flux and magnetic field. Magnetic flux is a measure of the total magnetic field passing through a given surface. Additionally, we represent it by using the symbol Φ (phi). We also measured it in webers (Wb). On the other hand, the magnetic field is the region in which magnetic forces act on magnetic materials or moving electric charges. It is represented by the symbol B.

Magnetic Flux Density Formula

The magnetic flux density formula is:

Magnetic field (B) = Magnetic flux (Φ) / Area (A)

Therefore, we can write the mathematical expression for magnetic flux density as:

B = Φ / A

Where: B = Magnetic flux density (tesla, T), Φ = Magnetic flux (weber, Wb), A = Cross-sectional area (square meters, m²).

After cross-multiplying the equation, we will have magnetic flux density equation as:

Φ = BA

As i mentioned earlier, we can use other si units like wb/m2, Tesla(T), and gauss to measure magnetic flux density. Below is an image of its definition and formula:

Magnetic force (F): Whenever a charge is moving in a magnetic field, it experiences a force which is also called magnetic force. The formula for magnetic force is

F = IBSinθ, [and I = QV]

The above equation shows that

F = QVBSinθ

For force carrying conductors in a magnetic field, we have

F = IBLSinθ or F = QVBLSinθ

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How to Calculate Magnetic Flux Density

Problem

The magnetic flux density of a 10m long stiff wire carrying a current of 4A is 0.8T. Calculate the force if it is lying in a direction at 600 to the magnetic field.

Solution

Data: We retrieve our data from the above question

Length (L) = 10m

Current (I) = 4A

Magnetic flux (Φ)= 0.8T

Force (F) = ?

Angle (θ) = 600

and the formula to use is F = IBLSinθ

Thus, by substituting our data into the above formula we have

F = 4 x 0.8 x 10 x Sin600

F = 32 x 0.866

Therefore, the final answer is 27.712

F = 27.712N

How is Magnetic Flux Density Produced?

Magnetic flux density, often denoted as B, is produced by the alignment and motion of electric charges, typically electrons, within a material. The primary contributors to magnetic flux density are current-carrying conductors and magnetic materials.

When an electric current flows through a conductor, it generates a magnetic field around it. The magnitude of this magnetic field is directly proportional to the current and is further influenced by the distance from the conductor. The relationship is described by Ampere’s Law.

Magnetic materials, such as ferromagnetic substances, play a significant role in producing magnetic flux density. In these materials, the alignment of atomic magnetic moments results in a cumulative effect, enhancing the overall magnetic field strength. The alignment occurs due to the intrinsic magnetic properties of the material.

Importance of Magnetic Flux Density

Magnetic flux density is a fundamental parameter in various applications, including:

Theories and Concepts Related to Magnetic Flux Density

We will now have a look at some key theories and concepts related to magnetic flux density:

1. Ampere’s Circuital Law

Ampere’s circuital law states that the magnetic field (B) around a closed loop is directly proportional to the current passing through the loop. Therefore, we have ampere’s circuital law formula as:

∮B · dl = μ₀ · I

Where:

∮B · dl = Closed loop integral of magnetic field (tesla-meter, T·m)

μ₀ = Permeability of free space (4π × 10-7 T·m/A)

I = Current passing through the closed loop (amperes, A)

2. Biot-Savart Law

The Biot-Savart law relates the magnetic field at a point due to a current-carrying conductor. Therefore, the Biot-savart law formula is:

dB = (μ₀ / 4π) * (I * dl × r) / r³

Where:

dB = Infinitesimal magnetic field element (tesla, T)

μ₀ = Permeability of free space (4π × 10-7 T·m/A)

I = Current in the conductor (amperes, A)

dl = Infinitesimal length element of the conductor (meters, m)

r = Distance from the conductor to the point where the field is measured (meters, m)

3. Magnetic Flux Density and Magnetic Permeability

Magnetic permeability (μ) is a material property that determines the material’s response to magnetic fields. It is a factor by which magnetic flux density is influenced in a material. Additionally, we can categorize magnetic materials into diamagnetic, paramagnetic, and ferromagnetic based on their magnetic permeability.

4. Magnetic Hysteresis

Magnetic hysteresis is a phenomenon where a magnetic material retains some magnetization even after the removal of an external magnetic field. It is very important in understanding the behaviour of ferromagnetic materials used in transformers and other devices.

5. Magnetic Field Lines

Magnetic field lines are imaginary lines used to visualize the direction of the magnetic field. They are drawn such that their direction is the same as the direction of the magnetic field at any given point.

Relationship Magnetic Flux Density and Magnetic Flux

You need to understand that there is a difference between magnetic flux density and magnetic flux. While they are related concepts, they refer to different aspects of a magnetic field.

Magnetic Flux Density:

Magnetic flux density, often denoted as (B), is a measure of how strong a magnetic field is at a particular point in space. It tells us how much force a magnetic field would exert on a charged particle moving through it. Additionally, the magnetic flux density is measured in units called teslas (T).

Magnetic Flux:

Magnetic flux, denoted as (Φ) (phi), is a quantity that represents the total magnetic field passing through a surface. It takes into account both the strength of the magnetic field (B) and the area (A) of the surface that the magnetic field lines pass through, as well as the angle (θ) between the magnetic field lines and the surface normal. Mathematically, magnetic flux (Φ) is given by the formula (Φ = BAcos(θ)), and its unit is the weber (Wb).

In simpler terms, think of magnetic flux density as a measure of how strong a magnetic field is at a specific spot, while magnetic flux considers not only the strength but also the amount of that magnetic field passing through a surface. Therefore, magnetic flux is a way to quantify the “amount” of magnetic field lines that cut through a surface.

Magnetic Flux Density and Magnetic Flux Table

Below is a table outlining the differences and relationship between magnetic flux density and magnetic flux:

Aspect Magnetic Flux Density Magnetic Flux
Definition A measure of magnetic field strength at a point A Measure of magnetic field passing through a surface
Symbol (B) (Φ)
Unit Tesla (T) Weber (Wb)
Formula N/A B = Φ = B x A cosθ
Factors Depends only on magnetic field strength (B) Depends on magnetic field strength (B), surface area (A), and angle (θ)
Measurement Indicates how strongly a magnetic field “pushes” Represents the “amount” of magnetic field lines passing through a surface
Use Case Helps understand the strength of a magnetic field Used when calculating magnetic effects on a surface or object
Relationship (B) is a component used in the formula for (Φ) (Φ) is calculated using (B), (A), and (θ)

Remember, magnetic flux density (B) focuses on the strength of a magnetic field at a specific point, while magnetic flux (Φ) considers both the strength and the area of a surface through which the magnetic field passes. The two concepts are related through the formula for magnetic flux.

Magnetic Flux Density formula Solenoid

A solenoid is like a coil of wire that creates a strong and controlled magnetic field when an electric current flows through it. The magnetic flux density (B) formula for a solenoid is :

B = μ₀ x n x I

Here is what each part of the formula means:

Therefore, when you multiply these three values together (permeability, turns per unit length, and current), you get the magnetic flux density inside the solenoid. This formula helps us understand and control the strength of the magnetic field generated by a solenoid, which is useful in various applications like electromagnets, speakers, and more.

Applications of Magnetic Flux Density

Magnetic flux density finds application in various fields. Some prominent examples include:

1. Electrical Engineering

In electrical engineering, magnetic flux density helps in designing transformers, motors, and generators. Understanding the behavior of magnetic fields is very important for optimizing these devices for efficiency and performance.

2. Material Science

Material scientists utilize magnetic flux density to study and characterize magnetic materials. By understanding the magnetic properties, they can develop materials suitable for specific applications, such as memory storage or magnetic shielding.

3. Medical Imaging

Magnetic resonance imaging (MRI) relies on the principles of magnetic flux density to create detailed images of internal body structures. It has become an indispensable tool in modern medicine for diagnosis and research.

4. Magnetic Levitation Trains

Magnetic levitation (maglev) trains use magnetic flux density to achieve frictionless movement and high speeds. The absence of physical contact between the train and the tracks reduces wear and energy consumption.

5. Magnetic Sensors

Magnetic flux density is employed in various sensors, such as compasses and magnetic encoders. These sensors are essential in navigation, robotics, and industrial automation.

FAQs

1. What is the difference between magnetic flux and magnetic flux density?

Magnetic flux is a measure of the total magnetic field passing through a given surface, while magnetic flux density refers to the amount of magnetic flux per unit area in a magnetic field. In other words, magnetic flux density describes the concentration of magnetic field lines.

2. How is magnetic flux density measured?

Magnetic flux density is measured using a device called a teslameter or gaussmeter. These instruments detect the strength of the magnetic field and provide readings in tesla (T) or gauss (G).

3. What are some practical applications of magnetic flux density in everyday life?

Some practical applications of magnetic flux density include electric motors in household appliances, magnetic locks in doors, and magnetic closures in bags and purses.

4. Can magnetic flux density be shielded or controlled?

The answer is yes, magnetic flux density can be shielded or controlled using magnetic shielding materials or by adjusting the current flow in conductors. Magnetic shields can redirect magnetic fields away from sensitive equipment.

5. How does magnetic flux density affect magnet strength?

Magnetic flux density is directly related to magnet strength. A higher magnetic flux density indicates a stronger magnetic field, resulting in more powerful magnets.

6. Are there any health risks associated with magnetic flux density?

In our daily activities, magnetic flux density from household items and electronic devices poses no health risks to humans. However, high magnetic flux density in industrial settings or medical equipment may require careful consideration to avoid potential health effects.

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