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5 marksInduced e.m.f.

CSEC Physics · May/June 2009 · Paper 2 · Question 5(b)(i)

An emergency flashlight (Figure 4) has a crank handle connected to an alternating current generator, rechargeable batteries, and LEDs. Turning the handle rotates a permanent magnet in the presence of a stationary coil, producing current to charge the batteries.

How is the electromotive force (e.m.f.) generated in the stationary coil?

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Other parts of this question

  1. 5(a)Sketch the magnetic field associated with (i) a single bar magnet and (ii) between two strong bar magnets with their north poles facing, and in line with, each…[4 marks]
  2. 5(b)(ii)What ADDITIONAL component is needed to be able to charge the batteries?[5 marks]
  3. 5(b)(iii)At a reasonable cranking rate, the unit generates 6.2 V. Calculate the current in the circuit if the resistance is 310 Ω.[5 marks]
  4. 5(c)(i)How many turns are needed in the secondary winding if the voltage is stepped up from 6.2 V to 15.5 V?[6 marks]
  5. 5(c)(ii)Given that the current in the primary winding is 10 mA, what power is transmitted to the secondary windings if the transformer is 77% efficient?[6 marks]

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