College Physics III – Thermodynamics, Electricity, and Magnetism
Definition
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.
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The magnetic field inside a long solenoid is given by $B = \mu_0 n I$, where $\mu_0$ is the permeability of free space, $n$ is the number of turns per unit length, and $I$ is the current.
The magnetic field outside a solenoid is nearly zero if the solenoid is long compared to its diameter.
The direction of the magnetic field inside a solenoid follows the right-hand rule: if you curl your fingers around the coil in the direction of current flow, your thumb points in the direction of the magnetic field.
Solenoids can be used to generate controlled magnetic fields for various applications including MRI machines, relays, and actuators.
When connected to an alternating current (AC) source, a solenoid can produce a changing magnetic field that induces an electromotive force (EMF) according to Faraday's Law.
Review Questions
What formula represents the magnetic field inside a long solenoid?
Describe how to determine the direction of the magnetic field inside a solenoid using your hand.
What happens to the magnetic field outside a very long solenoid?
Lenz's Law states that an induced EMF will always work in such a way as to oppose the change in flux that caused it.
\textit{Inductance}: \textit{Inductance} refers to the property of an electrical conductor or circuit that causes it to oppose changes in current flow, measured in Henrys (H).