Faraday's law of induction facts for kids
|Electricity · Magnetism|
Faraday's law of induction is a law of physics proposed by English physicist Michael Faraday in 1831. It is one of the basic laws of electromagnetism. The law explains the operation principles of generators, transformers and electrical motors.
Faraday's law of induction says that when a magnetic field changes, it causes a voltage. That phenomenon was also found by Joseph Henry in 1831. To describe the law, the magnetic flux and also a surface with a wire loop as border. This leads to the following surface integral:
When the flux changes, it produces electromotive force. The flux changes when B changes or when the wire loop is moved or deformed, or when both happens. The electromotive force can then be calculated with the following equation:
- is the electromotive force
- N is the number of loops the wire makes
- ΦB is the magnetic flux of one loop
Images for kids
Faraday's experiment showing induction between coils of wire: The liquid battery (right) provides a current which flows through the small coil (A), creating a magnetic field. When the coils are stationary, no current is induced. But when the small coil is moved in or out of the large coil (B), the magnetic flux through the large coil changes, inducing a current which is detected by the galvanometer (G).
A counterexample to Faraday's law when over-broadly interpreted. A wire (solid red lines) connects to two touching metal plates (silver) to form a circuit. The whole system sits in a uniform magnetic field, normal to the page. If the word "circuit" is interpreted as "primary path of current flow" (marked in red), then the magnetic flux through the "circuit" changes dramatically as the plates are rotated, yet the EMF is almost zero, which contradicts Faraday's law. After Feynman Lectures on Physics Vol. II page 17-3.
de:Elektromagnetische Induktion#Induktionsgesetz in Integralform
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