Chapter 25 - Electromagnetic induction Flashcards
How does a magnetic field induce a current in a wire?
Describe the process of electromagnetic induction.
The movement of a charged particle relative to a magnetic field causes it to experience a force.
The movement of a magnetic field relative to a charge will also create the same force on the charged particle.
If the charged particle is an electron in a wire, the force creates/induces a potential difference (known as an electromotive force (emf) if the wire is part of a complete circuit) as the electrons in the rod will build up on one side of the rod.
The emf forces the electrons around the circuit inducing a current.
This phenomenon also occurs if you move a bar magnet relative to a coil of wire, if the coil forms a complete circuit, a current is induced.
An emf is induced by changing the ______ ______ _______ through a conductor.
An emf is induced by changing the magnetic flux linkage through a conductor (to induce an emf in a conductor, the conductor must cut across the lines of flux of a magnetic field).
What are methods of inducing an emf (changing magnetic flux linkage)?
- Rotating a conductor within a magnetic field (like in a motor).
- Moving a conductor relative to a magnetic field.
- Continuously varying the magnitude of B of the magnetic field through a conductor.
What is Faraday’s law?
The magnitude of induced emf in a circuit is equal to the rate of change of flux linkage through the circuit.
Equation representing this law is in data sheet.
What is Lenz’s law?
The direction of induced current (and emf) is such as to oppose the motion causing it.
Explain how Lenz’s law is demonstrated by moving a bar magnet relative to a coil of wire.
The movement of the magnet relative to the coil of wire causes a change of flux linkage through the coil as the coil of wire cuts through the lines of flux of the magnet and so induces an emf in the coil, which induces a current to flow through the wire.
The induced current results in one end of the coil having a north polarity and the other end a south polarity.
Due to Lenz’s law, if a magnet is moving towards the coil of wire, the same pole as the pole of the magnet approaching the coil will be induced in order to repel the magnet (vice versa for a magnet moving away from the coil).
Works in a similar way if a conductor is moved relative to a magnetic field.
How can Lenz’s law be demonstrated by measuring the speed of a magnet falling through a coil of wire and its speed falling without a coil of wire?
As the magnet approaches the coil of wire, a north pole is induced at the top of the coil, repelling the magnet, reducing the magnets speed.
When in the coil, no emf is induced as there is no change of flux.
As the magnet is leaving the coil, a south pole is induced at the bottom of the coil, attracting the magnet, and reducing its speed.
What is the equation of the emf induced by a straight conductor moving in a magnetic field?
𝜀 = BLv
L = length of conductor v = speed of conductor.
What is the equation of the induced emf of a rectangular coil entering a uniform magnetic field?
𝜀 = NBLv
N = number of turns in coil
How does a AC generator work?
A current/emf is induced by spinning a rectangular coil in a uniform magnetic field. If the coil rotates at a constant frequency in a magnetic field, the magnetic flux linkage changes continuously.
In a rotating coil:
𝑁Ф = 𝐵ANcos(𝜔t)
𝜀 = 𝐵AN𝜔sin(𝜔t)
where 𝜀 is the induced emf
Charged particles in a magnetic field are deflected in a ______ path.
Charged particles in a magnetic field are deflected in a circular path.
