1 Answer

Answer :

Copper brushes in D.C. machine are used where low voltage and high currents are involved.

Related questions

Last Answer : The rapid wear of brushes takes place due to abrasion from dust, excessive spring pressure, rough commutator bars, high mica insulation between com-mutation bars.

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Last Answer : The number of brushes in a commutator depends on amount of current to be collected.

Last Answer : The material for commutator brushes is generally carbon.

Last Answer : Brushes of D.C. machines are made of carbon.

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Last Answer : Brushes of DC machine are made up of carbon.

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Last Answer : In a DC shunt generator working on load, the brushes are moved forward in the direction of rotation, as a result of this, commutation will Improve but terminal voltage will fall 

Last Answer : If brushes of a D.C. generator are moved in order to bring these brushes in magnetic neutral axis, there will be crossmagnetisation as well as demagnetising.

Last Answer : In D.C. generators, the brushes on commutator remain in contact with conductors which lie under interpolar region.

Description : Copper brushes in D.C. machine are used (a) where low voltage and high currents are involved (b) where high voltage and small cur-rents are involved (c) in both of the above cases (d) in none of the above cases

Last Answer : Ans: a

Description : Etched or burned bands on the contact faces of the brushes in a direct current generator can be caused by ____________. A. high mica segments B. copper drag on the commutator C. brushes improperly positioned D. copper embedded in the brushes

Last Answer : Answer: C

Description : The material for commutator brushes is generally (a) mica (b) copper (c) cast iron (d) carbon

Last Answer : Ans: d

Description : Brushes of D.C. machines are made of (a) carbon (b) soft copper (c) hard copper (d) all of above

Last Answer : Ans: a

Last Answer : In a D.C. machine stray loss is the sum of iron loss and mechanical loss.

Last Answer : In any rotating machine that part which houses the conductors and in which e.m.f. induced is to be utilised is called armature.

Last Answer : To avoid formation of grooves in the commutator of a D.C. machine the brushes of opposite polarity should track each other.

Last Answer : Open circuited armature coil of a D.C. machine is identified by the scarring of the commutator segment to which open circuited coil is connected and indicated by a spark completely around the commutator.

Last Answer : In case of D.C. machine winding, number of commutator segments is equal to number of armature coils.

Description : Eddy currents are induced in the pole shoes of a D.C. machine due to?

Last Answer : Eddy currents are induced in the pole shoes of a D.C. machine due to relative rotation between field and armature.

Last Answer : Armature reaction of an unsaturated D.C. machine is crossmagnetising.

Last Answer : Iron losses in a D.C. machine are independent of variations in load.

Last Answer : In a four-pole D.C. machine alternate poles are north and south.