Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Electrostatics wikipedia , lookup
Field (physics) wikipedia , lookup
Condensed matter physics wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Maxwell's equations wikipedia , lookup
Electromagnetism wikipedia , lookup
Neutron magnetic moment wikipedia , lookup
Magnetic field wikipedia , lookup
Magnetic monopole wikipedia , lookup
Aharonov–Bohm effect wikipedia , lookup
Superconductivity wikipedia , lookup
Electricity and Magnetism Electromagnetic Induction Mr D. Patterson Outcomes • describe and apply the concepts of magnetic flux and magnetic induction—this will include applying the relationships: • describe the production of an induced emf by the relative motion of a straight conductor in a magnetic field—this will include applying the relationship: • An electric motor generator usesuses electricity motiontotoproduce produce movement electric current Simple example Explanation • Electric charges cutting across magnetic field lines will feel a force • The conductor must be moving perpendicular to the magnetic field V Emf • The separation of charge is similar to a battery • An EMF is produced! V • No current however as the “battery” is not connected to a circuit Current • If there is a complete circuit the EMF will force a current to flow. V • This process of generating an electric current using a magnetic field is called electromagnetic induction. • “An EMF is induced in the conductor” • “The induced current flows through an external circuit” Formula • The EMF induced in a conductor: • • • • ε is the EMF (V) l is the length of the conductor (m) v is the velocity of the conductor (ms-1) B is the magnetic flux density (T) Magnetic Flux • The magnetic flux is a measure of the total magnetic field in a given area is the magnetic flux (Wb) B is the magnetic flux density (T) A is the perpendicular area (m2) Faraday’s and Lenz’s Law • Faraday’s Law: • The induced EMF in a single coil is equal to the negative rate of change of magnetic flux through that coil There are multiple ways to Induce an EMF Lenz’s Law • Lenz’s Law: • An induced current will create a magnetic field which opposes the change in magnetic field that created the current • This is the reason for the negative sign in the formula Using the right hand rule with Lenz’s Law • For a straight conductor: Swap the direction of the magnetic field to find the induced current V Using the right hand rule with Lenz’s Law • For a coil: Create a magnetic field inside the coil which is opposite to the changing magnetic field • OR create a magnet inside the coil whose poles will resist the motion of the external magnet Using the right hand rule with Lenz’s Law • If a magnet is stationary in (or near) the coil, there is no change in flux, so no induced EMF or current Using the right hand rule with Lenz’s Law • For a coil: Create a magnetic field inside the coil which is opposite to the changing magnetic field • OR create a magnet inside the coil whose poles will resist the motion of the external magnet Size of the induced magnetic field depends on size of the induced current N N Small resistance N Large resistance No resistor (Infinite resistance) Example Problem • A square coil is free to rotate about its central axis and is perpendicular with an external magnetic field. The coil rotates 90 deg until it is parallel with the field in 12.0 ms. The external magnetic field has a flux density of 850 mT. + A - • a) What is the initial magnetic flux passing through the coil? • b) What is the final magnetic flux passing through the coil? • c) What is the average EMF produced from the rotation? • d) Will the reading on the ammeter be positive or negative? 8.50 cm