{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

# L30_a - FARADAY'S LAW OF INDUCTION(Chapter 23 Look at a...

This preview shows pages 1–5. Sign up to view the full content.

FARADAY’S LAW OF INDUCTION – (Chapter 23) Look at a conductor moving ACROSS magnetic field lines Free electrons move perpendicular to B r (into page) o Electrons (neg.) feel force B v e F r r r × = Force on electrons is down o Result is potential difference induced between ends of bar – bottom more negative CONCLUSION: potential difference can be induced across a conductor moving through a magnetic field Will come back to this example later when we have more theory v F B in

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
SOME DEMONSTRATIONS: A magnet moving into/out of a loop of wire induces a current o See fig. 23.2 in text Starting/stopping current through loop in one coil (primary) causes pulse of current in coil (secondary) linked by iron coil - this is a transformer o See fig. 23.3 in text FARADAY’S CONCLUSION from observations like these: Time-varying magnetic fields can induce currents To quantify, need to relate induced potential difference to changing magnetic flux Ammeter N S Ammeter primary secondary iron switch battery
MAGNETIC FLUX: proportional to number of magnetic field lines through area area element A d r : vector perpendicular to area element contribution to magnetic flux from A d r is A d B r r Total flux through area is = Φ area B A d B r r Unit for flux is T m 2 Wb (1 Weber) emf – symbol is ε Work to push unit charge through a wire (or space) Units of emf are volts originally “electromotive force” BUT not a force: long name no longer used If resistance in loop is R, then current in loop is R I / ε = dA B θ Battery is source of emf

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document