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ELECTROMAGNETISM P60 015 (a) In
a real generator, why does the rotating coil have many turns rather than a
single loop of wire? Explain. (b) When
a generator is supplying current to an external circuit, it is found that the
force required to keep the coil turning is greater than the force needed to
rotate the coil when the external circuit is not connected to the generator.
Explain. (c) The diagram shows two generator coils, one
with one loop and the other two loops at right angles to each other.
(i)
Describe the commutators that are used for
a DC and an AC generator. (ii)
What is the function of the brushes? (iii)
Draw the DC and AC outputs for the two
generators. (d) Discuss the advantages and disadvantages of
DC and AC generators. View solution below only after you have completed the answering the question. |
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Solution (a) By
using a coil rather than a loop the magnetic flux through the whole circuit
is increased in proportion to the number of turns. Thus, the change in flux
during each revolution is increased and so is the magnitude of the induced emf. (b) The
rotating coil represents a current carrying conductor moving in a magnetic
field. This conductor experiences a force that always opposes the motion - Lenz’s
law. The greater the speed of rotation the greater the induced current and
the greater the opposing torque. (c) Brushes
enable the generator to be connected to the external circuit without the
wires becoming increasing tangled together as the armature in the generator
rotates. DC generator
uses a single split ring commutator
ac generator
uses a pair of rings as a commutator
(d) The advantage of a DC generator is that the current in the
external circuit is DC – the direction of the current is constant although
its magnitude continually changes.
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VISUAL PHYSICS ONLINE http://www.physics.usyd.edu.au/teach_res/hsp/sp/spHome.htm If you have any feedback, comments,
suggestions or corrections please email: ian.cooper@sydney.edu.au Ian Cooper
School of Physics University
of Sydney |
