Electromagnetic induction
Section: Electricity & Magnetism | Syllabus: Cambridge AS Level Physics 9702
What is Electromagnetic Induction? Electromagnetic induction is the production of an e.m.f. (and hence current in a closed circuit) when there is relative motion between a conductor and a magnetic field.
Two Ways to Induce an E.M.F. A conductor moving across a magnetic field A changing magnetic field linking with a conductor Demonstrating Electromagnetic Induction Experiment 1: Moving Wire Connect a wire to a sensitive galvanometer Move the wire rapidly between the poles of a magnet Observe: galvanometer needle deflects (e.m.f.
induced) Stop moving: needle returns to zero (no e.m.f.) Experiment 2: Moving Magnet and Coil Connect a coil of wire to a galvanometer Move a bar magnet into the coil Observe: galvanometer deflects in one direction Move magnet out: deflection in opposite direction Magnet stationary inside coil: no deflection FIG 4.5.2: Electromagnetic induction with coil and magnet Coil connected to galvanometer.
Bar magnet being pushed into coil causes needle deflection. When magnet pulled out, deflection reverses. Key point: e.m.f. induced only when there is relative motion. Factors Affecting Induced E.M.F. The magnitude of the induced e.m.f.
can be increased by: Increasing the speed of movement (faster motion) Using a stronger magnet (greater field strength) Increasing the number of turns on the coil Using a larger area of coil (more field lines cut) No E.M.F.
Induced When There is no relative motion between the conductor and magnetic field (both stationary relative to each other). Direction of Induced E.M.F. The direction of the induced e.m.f. (and current) always opposes the change that produces it.
Lenz's Law Concept If you push a N pole into a coil, the induced current creates a N pole at that end of the coil to oppose the incoming magnet. Reversing the direction of motion or the magnetic field direction reverses the direction of the induced e.m.f.
Applications of Electromagnetic Induction Generators: Convert kinetic energy to electrical energy Transformers: Change a.c. voltages Microphones: Convert sound to electrical signals Induction hobs: Heat cooking pans using induced currents
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