College Physics III – Thermodynamics, Electricity, and Magnetism
Definition
Motional emf is the electromotive force (emf) induced in a conductor moving through a magnetic field. It arises due to the Lorentz force acting on the charges within the conductor.
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The magnitude of motional emf can be calculated using the formula $\mathcal{E} = B \ell v \sin(\theta)$, where $B$ is the magnetic field strength, $\ell$ is the length of the conductor, $v$ is its velocity, and $\theta$ is the angle between velocity and magnetic field.
Motional emf is an application of Faraday's Law of Induction.
The direction of motional emf can be determined using Fleming's Right-Hand Rule.
Motional emf plays a crucial role in electric generators where mechanical energy is converted into electrical energy.
If a closed loop moves through a magnetic field, an induced current will flow as long as there is a change in flux.
Review Questions
What formula do you use to calculate motional emf?
How do you determine the direction of motional emf?
Explain how motional emf applies to electric generators.
Related terms
Faraday's Law of Induction: A fundamental law stating that an electromotive force is induced in a circuit when there is a change in magnetic flux through the circuit.
The force exerted on a charged particle moving through an electric and magnetic field, given by $\mathbf{F} = q(\mathbf{E} + \mathbf{v} \times \mathbf{B})$.
Fleming's Right-Hand Rule: A mnemonic used to predict the direction of induced current; point your thumb in the direction of motion, your index finger in the direction of the magnetic field, and your middle finger will point in the direction of current.