Magnetic Field Lines: Magnetic field is an important topic in physics, which starts to elaborate at the secondary level. CBSE introduces this topic in Class 10 and then dives into details in further standards. Such topics include advanced commitment from teachers as well as students to understand the things that you cannot see but have experienced.
In this concept explainer, the magnetic field formula, principle, properties, and applications have been provided along with proper illustrations. Let’s learn together!
Magnetic Field Definition
Have you ever wondered how magnets attract other magnets and certain metallic items like coins? This attraction intensify as you move the item closer but decreases you move it away. This happens because of magnetic filed.
Magnetic field is a region of space where the magnet exerts a magnetic force on any other magnetic objects or moving electrically charged particles. It act as an aura of magnetism that can attract or repel objects depending on their properties. The magnetic field is invisible, but its effects are undeniable! Understanding magnetic fields helps in advancing technology and improving safety and efficiency in numerous applications.
Fundamental Concepts of Magnetism
Magnetism is a physical phenomenon created from the motion of electrons that leads to generation of forces that attract or repel objects. It is originated from the movement and spin of electrons in the atomic orbitals. These electron movements create magnetic dipoles aligning to form magnetic domains in materials like iron, cobalt, and nickel. The uniform alignment of these domains create strong magnetic properties of the material.
Earth's magnetism, or geomagnetism, is generated by the movement of molten iron and other metals in its outer core, creating a magnetic field that extends into space and affects compasses and animal navigation
Electromagnetism
It is an interconnected aspect of electricity and magnetism. When an electric current flows through a conductor, it generates a magnetic field around it, as described by Ampère's Law. Conversely, a changing magnetic field can induce an electric current in a conductor, as stated by Faraday's Law of Electromagnetic Induction. This relationship forms the basis for many technologies, including electric motors, generators, and transformers. These principles are also a part of the operation of electromagnetic waves, such as light and radio waves, as described by Maxwell's equations.
Magnetic Poles
Magnetic poles are the areas of the magnet where the magnetic force is highest. Such areas are termed as north and south poles. Outside a magnet, the magnetic field lines originate from north pole and end at south pole. Reverse happens inside the magnet. Because of this the opposite poles of the magnet attract each other while the like poles repel.
Earth itself acts like a giant magnet with a magnetic north and south pole, which is essential for navigation using compasses and influences various natural phenomena like auroras.
Sources of Magnetic Field
There are various sources of magnetic fields with unique characteristics and principles of generation. The primary sources of magnetic fields include:
- Permanent Magnets: These materials, like iron, cobalt, and nickel does not need an external source of energy to create magnetic field. They have persistent magnetic fields because these electrons exhibit a special alignment of their spins, creating a collective magnetic effect.
- Electric Currents: According to Ampère's Law, a magnetic field is produced around a conductor carrying an electric current. This principle is used in electromagnets, where coils of wire generate strong magnetic fields when current flows through them.
- Earth's Magnetic Field: Generated by the movement of molten iron and other metals in Earth's outer core, this geodynamo effect creates a magnetic field that extends into space and influences compass navigation. This is why Earth has also given magnetic poles as north and south.
- Electromagnetic Induction: Changing magnetic fields can induce electric currents, which in turn produce magnetic fields. This principle, described by Faraday's Law, underlies the operation of transformers, generators, and induction cooktops.
- Subatomic Particles: Particles such as electrons have intrinsic magnetic moments due to their spin and orbital motion, contributing to atomic and molecular magnetism.
- Magnetic Materials: Certain materials, known as ferromagnetic, ferrimagnetic, and paramagnetic, exhibit magnetic properties that enhance or interact with external magnetic fields.
- Solar and Cosmic Phenomena: Magnetic fields are also found in solar and cosmic contexts, such as the Sun's magnetic field influencing solar flares and the interstellar magnetic fields affecting cosmic rays.
Properties of Magnetic Field
There are numerous properties of magnetic fields that define their behaviour and interactions with material and other charged particles. Some of the properties are mentioned here:
- Magnetic Field Lines: These are the imaginary lines that are used to represent the magnetic field. North pole is the origin for these lines which enters at south pole forming closed loops. The density of magnetic filed lines indicate the strength of magnetic field.
- Magnetic Flux (Φ): It is a measure of the quantity of magnetism, considering the strength and extent of a magnetic field. It is proportional to the number of magnetic field lines passing through a given area. The unit of magnetic flux is the Weber (Wb).
- Vector Nature: Magnetic fields have both magnitude and direction. Thus, these are vector fields. The direction of the magnetic field at any point is the direction in which the north pole of a compass needle points.
- Magnetic Force: A magnetic field exerts a force on moving charged particles and on magnetic dipoles. The force on a moving charge is given by the Lorentz force law: F=q(v×B), where q is the charge, v is the velocity, and B is the magnetic field.
Magnetic Field Units of Measurement
Magnetic field strength, or magnetic flux density, is a critical parameter in physics and engineering, quantified by units such as Tesla (T) and Gauss (G).
Tesla (T):
- The Tesla is the SI unit of magnetic field strength.
- Defined as one weber per square meter (1 T=1 Wb/m2).
- Named after the inventor and electrical engineer Nikola Tesla.
- Commonly used in scientific and engineering contexts, particularly in streams with strong magnetic fields, such as MRI machines, particle accelerators, and electromagnetic research.
Gauss (G):
- The Gauss is a CGS (centimetre-gram-second) unit of magnetic field strength.
- Defined as one maxwell per square centimeter (1 G=1 Mx/cm2).
- Named after the German mathematician and physicist Carl Friedrich Gauss.
- Primarily used in contexts dealing with weaker magnetic fields, such as Earth's magnetic field and magnetic fields in consumer electronics.
- Conversion: 1 T=10,000 G
Magnetic Field Theories and Laws
Biot-Savart Law:
- Describes the magnetic field generated by a steady electric current.
- The law states that the magnetic field B at a point in space is proportional to the current III and inversely proportional to the square of the distance r from the current element.
- Mathematically expressed as: dB=(μ0/4π) (dl×r/r3)
- This law is crucial for calculating the magnetic field produced by complex current distributions.
Ampère's Law:
- Relates the magnetic field around a closed loop to the electric current passing through the loop.
- The integral form of Ampère's Law is: ∮B⋅dl=μ0Ienc
- This law is particularly useful in determining the magnetic field in highly symmetric situations, such as around a long straight wire or within a solenoid.
Faraday's Law of Electromagnetic Induction:
- Explains how a changing magnetic field induces an electric current in a conductor.
- The law is mathematically expressed as: ε=−dΦB/dt
- Here, ε is the induced electromotive force (emf) and ΦB is the magnetic flux.
- This principle is the basis for many electrical generators and transformers.
Applications of Magnetic Fields
- Medical Imaging: Magnetic resonance imaging (MRI) machines use strong magnetic fields and radio waves to create detailed images of organs and tissues inside the body.
- Electromagnetic Devices: Used in electric motors, generators, transformers, and inductors to generate, transmit, and transform electrical energy.
- Navigation: Compasses rely on Earth's magnetic field for navigation, and magnetometers are used in navigation systems.
- Research and Testing: Magnetic fields are used in laboratories for experiments in physics, chemistry, and materials science, including studying magnetic materials and properties.
- Electrical Appliances: Speakers, headphones, and microphones use magnetic fields to convert electrical signals into sound and vice versa.
Magnetic Field Around Straight Wire
The magnetic field around a straight wire is circular and follows the right-hand rule. When an electric current flows through the wire, it generates a magnetic field concentrically surrounding the wire. The strength of the magnetic field decreases with distance from the wire according to the inverse square law. The direction of the magnetic field lines is determined by the direction of the electric current: they circulate counterclockwise if viewed in the direction of current flow when grasping the wire with the right hand. This phenomenon forms the basis for electromagnets and is fundamental in understanding electromagnetic induction and related technologies.
Image Source: Quora
Magnetic Field Around Circular Loop
The magnetic field around a circular loop of wire is similar to that of a bar magnet. When an electric current flows through the loop, it generates a magnetic field. Inside the loop, the magnetic field lines form concentric circles with the direction given by the right-hand rule. The magnetic field is strongest at the center of the loop and weaker farther away, following an inverse square law. Outside the loop, the magnetic field resembles that of a dipole, with field lines emerging from one side and re-entering on the opposite side.
Image Source: Topper
Magnetic Field Diagrams
Magnetic Field Around a Bar Magnet
Magnetic Field Due to a Current-Carrying Conductor
Image Source: GeeksforGeeks
Earth’s Magnetic Field
Image Source: Physics Magazine
This completes the basic explanation of magnetic fields that students can use to get a broader idea about the topic. To get further knowledge on this topic, refer to the reference links below:
References and Further Reading
- Books
NCERT Class 10 Science Textbook PDF
NCERT Class 12 Physics Textbook PDF
- Articles
Magnetic effects of Electric Current
- Online Resources