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Electromagnetic

Electromagnetic. Induction. Conductor moving in magnetic field. x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x. +++. F=qE. v. L. F=qvB. ----. As a conductor moves through a B-field, charges separate due to magnetic force.

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Electromagnetic

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  1. Electromagnetic Induction

  2. Conductor moving in magnetic field x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x +++ F=qE v L F=qvB ---- • As a conductor moves through a B-field, charges separate due to magnetic force. • The separation of charge creates a uniform e-field within the conductor. • Wire is in electromagnetic equilibrium when • The presence of an e-field creates a potential difference between the ends of the conductor. (Since –ive charges accumulate at the lower end, the upper end is at a higher electric potential. A voltage is “induced” by the motion.)

  3. Rail System i x x x x x x x x x x x x R v L The induced current, itself a product of the field, will interact with the field and feel a force. What direction will this force be in? By open RHR, the magnetic force on the rod is to the left, opposing the motion that is causing the current. Lenz’s Law:the induced current will always flow in such a way as to oppose the change that caused it.

  4. Magnetic flux • Measures the “amount” of field cutting through an area Magnetic flux is measured in units called Weber [Wb] 1 Wb = 1 Tm2

  5. Let us analyze the rail system in terms of magnetic flux: i x x x x x x x x x x x x R v L x In a time ∆t the rod moves a distance ∆x and this causes a change in the flux cutting through the loop.

  6. Faraday’s Law The rate at which the flux changes through a loop will equal the induced voltage around the loop. Note: the negative sign indicates the direction of the induced current.

  7. Exercise: A coil of 50 windings each with radius 10 cm, is initially oriented so that a uniform B field of .2 T is perpendicular to the cross sectional area. In the next .14 sec, field is reduced to .15 T. Find the average induced voltage in the coil over this time interval.

  8. Faraday’s Law: Generalized • A loop moving in a field has a current induced (Think F=qvB) • If the loop is stationary, and the magnet moves, a current is still created! Why? • Charges in the loop “see” a changing magnetic field, and this creates an electric field. • This electric field moves the charges and causes the current.

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