11.2 Magnetic Fields and Lines
3 min read•june 24, 2024
Magnetic fields are invisible forces that affect moving electric charges. They're all around us, from Earth's guiding compasses to the fields in your phone's speakers. Understanding how they work is key to grasping electromagnetism.
help us visualize these forces. They show the field's direction and strength, always forming closed loops. This concept is crucial for understanding how magnets and electric currents create and interact with magnetic fields.
Magnetic Fields and Lines
Definition of magnetic fields
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- A region in space where a moving electric charge experiences a force due to its motion
- The force experienced by a moving charge in a magnetic field is called the ()
- Magnetic force on a moving charge is given by
- represents the charge of the particle
- represents the velocity of the charge
- represents the magnetic field vector
- Magnitude of the magnetic force is
- is the angle between the velocity vector and the magnetic field vector
- Magnetic force is always perpendicular to both the velocity and magnetic field vectors ()
- SI unit for magnetic field strength is the (T)
- 1 T = 1 N/(A·m)
- Examples of magnetic fields:
- Earth's magnetic field (compass)
- Magnetic fields generated by bar magnets or electromagnets
Right-hand rule for magnetic forces
- Determines the direction of the magnetic force on a moving charge using the right hand
- For a positively charged particle:
- Point right thumb in the direction of the particle's velocity ()
- Curl fingers in the direction of the magnetic field ()
- Palm points in the direction of the magnetic force ()
- For a negatively charged particle, the magnetic force direction is opposite to that determined by the for a positive charge
- Consistent with the cross product in the magnetic force equation
- Examples:
- Determining the direction of force on a proton moving through a magnetic field
- Predicting the motion of an electron beam in a (CRT)
- The combination of electric and magnetic forces on a charged particle is known as the
Visualization of magnetic field lines
- Visual representation of the magnetic field in space
- Properties of :
- Direction of the magnetic field at any point is tangent to the field line
- Density of field lines indicates the strength of the magnetic field
- Closely spaced lines represent a strong magnetic field
- Widely spaced lines represent a weak magnetic field
- Always form closed loops, starting and ending at the source of the magnetic field
- Never cross or diverge
- Magnetic field lines for a bar magnet:
- Exit the and enter the
- Field is strongest near the poles, where lines are most dense
- Magnetic field lines for a current-carrying wire:
- Form concentric circles around the wire
- Direction determined by the right-hand rule for a current-carrying wire
- Grasp the wire with your right hand
- Point thumb in the direction of the current
- Fingers will curl in the direction of the magnetic field lines
- Examples:
- Sketching field lines around a bar magnet
- Visualizing the magnetic field generated by a or a
Magnetism and Related Phenomena
- is the fundamental force responsible for the behavior of magnetic fields and their interactions with charged particles and materials
- is the process by which a changing magnetic field induces an electric current in a nearby conductor
- is a type of magnetism where certain materials (like iron) can become permanently magnetized and exhibit strong magnetic properties
Key Terms to Review (22)
Cathode-Ray Tube: A cathode-ray tube (CRT) is a specialized vacuum tube that generates and projects a beam of electrons onto a phosphor-coated screen, producing a visible image. This technology was widely used in early television sets and computer monitors, and is a crucial component in understanding the behavior of magnetic fields and their applications.
Electromagnetic Induction: Electromagnetic induction is the process by which a changing magnetic field induces an electromotive force (EMF) in a conductor, causing an electric current to flow. This phenomenon is fundamental to the operation of many electrical devices and is crucial in understanding the relationship between electricity and magnetism.
Ferromagnetism: Ferromagnetism is a property of certain materials that exhibit strong magnetic behavior due to the alignment of their magnetic moments in the same direction. This phenomenon occurs when the material's atomic structure allows for cooperative interactions among neighboring atoms, resulting in a net magnetization even in the absence of an external magnetic field. The historical discoveries related to magnetism highlighted ferromagnetism as a crucial aspect of how materials respond to magnetic fields, while understanding magnetic fields and lines helps to visualize how ferromagnetic materials interact within those fields.
Gauss: The gauss (G) is a unit of magnetic induction or magnetic flux density in the centimeter-gram-second (CGS) system of units. One gauss is defined as one maxwell per square centimeter.
Lorentz Force: The Lorentz force is the force exerted on a charged particle when it moves through a magnetic field. It is a fundamental concept in electromagnetism that describes the interaction between electric and magnetic fields and the motion of charged particles.
Lorentz force equation: The Lorentz force equation describes the force experienced by a charged particle moving through an electric and magnetic field. It is given by $\mathbf{F} = q(\mathbf{E} + \mathbf{v} \times \mathbf{B})$, where $q$ is the charge, $\mathbf{E}$ is the electric field, $\mathbf{v}$ is the velocity of the particle, and $\mathbf{B}$ is the magnetic field.
Magnetic Field: A magnetic field is a region of space where magnetic forces can be detected. It is a fundamental concept in electromagnetism, describing the invisible lines of force that surround and permeate magnetic materials, electric currents, and changing electric fields. The magnetic field plays a crucial role in various topics within the study of college physics.
Magnetic field lines: Magnetic field lines are imaginary lines that represent the direction and strength of a magnetic field. They emerge from the north pole of a magnet and enter the south pole, forming continuous loops.
Magnetic Field Lines: Magnetic field lines are the invisible lines that represent the direction and strength of a magnetic field. They are used to visualize and understand the behavior of magnetic fields, which are crucial in various topics related to electromagnetism and electromagnetic induction.
Magnetic force: Magnetic force is the force exerted by a magnetic field on a moving electric charge or a current-carrying conductor. It is perpendicular to both the velocity of the charge and the magnetic field.
Magnetic monopoles: Magnetic monopoles are hypothetical particles that possess a single magnetic pole, either north or south, unlike conventional magnets which have both. They have not been observed experimentally but are predicted by certain theories in physics.
Magnetism: Magnetism is a fundamental force of nature that arises from the motion of electric charges. It is responsible for the attractive and repulsive forces observed between magnetic materials, and it plays a crucial role in the behavior of electric currents and the structure of the universe.
North Pole: The north pole is the point on the Earth's surface that is farthest north, where the Earth's axis of rotation meets its surface. It is one of the two points where the Earth's axis of rotation intersects its surface, the other being the south pole. The north pole is the location of the Earth's magnetic north, which is distinct from the geographic north pole.
Right-hand rule: The right-hand rule is a mnemonic used to determine the direction of the magnetic field surrounding a current-carrying conductor. Point your thumb in the direction of the current and curl your fingers; your fingers indicate the direction of the magnetic field lines.
Right-Hand Rule: The right-hand rule is a mnemonic device used to determine the direction of various quantities related to electromagnetism, such as the direction of magnetic fields, the motion of charged particles in magnetic fields, and the direction of the magnetic force on a current-carrying conductor. It provides a simple and intuitive way to visualize and remember these directional relationships.
Right-hand rule-1: Right-hand rule-1 is a mnemonic used to determine the direction of the magnetic force on a positive charge moving in a magnetic field. Point your thumb in the direction of the velocity, your fingers in the direction of the magnetic field, and your palm will point in the direction of the force.
Solenoid: A solenoid is a coil of wire designed to create a uniform magnetic field in its interior when an electric current passes through it. It is commonly used in electromagnets, inductors, and valves.
Solenoid: A solenoid is a tightly wound coil of wire, often cylindrical in shape, that produces a magnetic field when an electric current passes through it. Solenoids are fundamental components in the study of electromagnetism and have applications in various areas of physics, including magnetic fields, magnetic force, and electromagnetic induction.
South Pole: The south pole is one of the two points on the Earth's surface where the planet's axis of rotation meets its surface. It is the southernmost point on the globe and is the location of the Earth's magnetic south pole, which is the point where the Earth's magnetic field lines converge and exit the planet's surface.
Tesla: The tesla (T) is the SI unit of magnetic flux density, representing the strength of a magnetic field. One tesla is defined as one weber per square meter.
Tesla: The tesla (T) is the unit of magnetic flux density, or magnetic field strength, in the International System of Units (SI). It is named after the Serbian-American inventor Nikola Tesla, who made significant contributions to the field of electromagnetism. The tesla is a fundamental unit that is essential in understanding and describing various electromagnetic phenomena and their applications.
Toroid: A toroid is a three-dimensional geometric shape that resembles a doughnut or an inner tube. It is characterized by a circular path or loop, with the cross-section of the loop typically circular or elliptical. Toroids are commonly encountered in various physics topics, including magnetic fields, electromagnetic induction, and self-inductance.