23.3 Motional Emf
2 min read•june 18, 2024
is a fascinating phenomenon where changing magnetic fields create electric currents. , a specific type, occurs when conductors move through magnetic fields. This process is crucial for many everyday devices, from electric guitars to generators.
Understanding motional EMF involves key concepts like and . These principles explain how moving conductors in magnetic fields generate electricity, and why induced currents flow in specific directions. This knowledge is essential for grasping the workings of various electrical machines.
Motional EMF
Electromagnetic Induction and Motional EMF
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- Electromagnetic induction: process of generating electric current by changing magnetic field
- Motional emf () generated when a conductor moves through a magnetic field (a specific form of electromagnetic induction)
- Formula:
- magnetic field strength (also known as )
- length of the conductor
- velocity of the conductor perpendicular to the magnetic field
- Examples: electric guitar pickups, electric generators
- Formula:
- Faraday's law: relates the induced (emf) to the rate of change of magnetic
- Flux: measure of the total magnetic field passing through a given area
Emf, force, and work calculations
- Force on a current-carrying conductor in a magnetic field:
- current in the conductor
- angle between the current direction and the magnetic field
- Maximum force occurs when current is perpendicular to magnetic field ()
- Examples: electric motors, loudspeakers
- Work done by magnetic force on a moving conductor:
- displacement of the conductor in the direction of the force
- Work done depends on the force and the distance the conductor moves
- Examples: electric generators, transformers
Generation of motional emf
- When a conductor moves through a magnetic field, free electrons in the conductor experience a force due to the magnetic field
- This force causes electrons to move, creating an in the conductor
- Induced emf depends on velocity of conductor, strength of magnetic field, and length of conductor in the magnetic field
- Examples: dynamos, alternators
- Direction of induced current determined by Lenz's law
- Induced current creates a magnetic field that opposes the change in magnetic flux caused by the conductor's motion
- Examples: eddy current brakes, induction cooktops
Lenz's law in induced currents
- Lenz's law states that direction of induced current in a conductor is such that it opposes the change that caused it
- In motional emf, induced current creates a magnetic field that opposes the change in magnetic flux caused by the conductor's motion
- To determine direction of induced current:
- Use to find direction of magnetic force on the conductor
- Induced current will flow in direction opposite to the magnetic force
- Examples:
- Electromagnetic braking in trains
- Back emf in electric motors
Key Terms to Review (14)
$ ext{mathcal{E}} = ext{Blv}$: $ ext{mathcal{E}} = ext{Blv}$ is an equation that represents the motional electromotive force (emf) induced in a conductor moving through a magnetic field. It states that the induced emf ($ ext{mathcal{E}}$) is directly proportional to the strength of the magnetic field (B), the length of the conductor (l), and the velocity of the conductor (v) as it moves through the field.
$F = IlB\sin\theta$: $F = IlB\sin\theta$ is an equation that describes the force experienced by a current-carrying conductor placed in a magnetic field. This force, known as the motional electromotive force (emf), is generated when the conductor moves through the magnetic field at an angle $\theta$ relative to the field direction.
$W = F \cdot d$: The equation $W = F \cdot d$ represents the work done by a force $F$ acting on an object over a displacement $d$. This fundamental equation is a core concept in physics, connecting the amount of work performed to the force applied and the distance moved.
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 the fundamental principle behind the operation of many electrical devices and systems, including transformers, generators, and motors.
Electromotive force: Electromotive force (emf) is the energy provided by a source per unit charge to move electrons through a circuit. It is measured in volts (V) and drives the current around the circuit.
Electromotive Force: Electromotive force (EMF) is the voltage or potential difference generated in an electrical circuit, typically by a source of electrical energy such as a battery or generator. It represents the driving force that causes electric charge to flow through a circuit, enabling the conversion of other forms of energy into electrical energy.
Faraday's Law: Faraday's law describes the relationship between a changing magnetic field and the electric field it induces. It states that the magnitude of the induced electromotive force (emf) in a circuit is proportional to the rate of change of the magnetic flux through the circuit.
Flux: Flux is a measure of the amount of a physical quantity, such as energy or particles, that passes through a given surface or area per unit of time. It is a fundamental concept in physics that is crucial for understanding various phenomena, including electric fields, magnetic fields, and the flow of fluids.
Induced Current: Induced current refers to the flow of electric current that is generated in a conductor when it experiences a changing magnetic field. This phenomenon is a fundamental principle in electromagnetism and is the basis for the operation of many electrical devices and machines.
Lenz's Law: Lenz's law is a fundamental principle in electromagnetism that describes the direction of the induced current or electromotive force (emf) generated by electromagnetic induction. It states that the direction of the induced current is always such that it opposes the change in the magnetic field that caused it, in accordance with Faraday's law of induction.
Magnetic Flux Density: Magnetic flux density, also known as magnetic induction or magnetic field strength, is a measure of the strength of a magnetic field. It quantifies the amount of magnetic flux per unit area perpendicular to the direction of the field. This term is crucial in understanding various electromagnetic phenomena, including the force on a moving charge, the Hall effect, the magnetic force between parallel conductors, motional electromotive force (emf), and eddy currents.
Motional EMF: Motional EMF, also known as the electromotive force (EMF) induced by motion, is the voltage generated when a conductor moves through a magnetic field. This phenomenon is a fundamental principle in the field of electromagnetic induction, which describes the generation of electric currents and voltages due to changing magnetic fields.
Right-hand rule: The right-hand rule is a mnemonic used to determine the direction of angular momentum vectors. It states that if you curl the fingers of your right hand in the direction of rotation, your thumb points in the direction of the angular momentum vector.
Right-Hand Rule: The right-hand rule is a mnemonic device used to determine the direction of various vector quantities in physics, such as magnetic fields, angular momentum, and the force on a moving charge in a magnetic field. It is a simple and intuitive way to visualize the relationship between these vectors and their associated directions.